Keywords: words:apple peel, polyphenols, ultrasound, selective extraction, cavitation phenomenon, cell damage, adsorption/desorption, membrane electro-filtration

This thesis focuses on the intensification of polyphenols extraction from apple products (flesh, peel, and pomace) by ultrasound (US) and the purification of apple peel extracts by adsorption/desorption and membrane technology.

The selective extraction of phenolic contents from apple products has been analyzed. The obtained data evidenced the possibility of fine regulation of selective extraction of soluble matter, catechin and total polyphenolic compounds using different temperatures, ultrasoundassisted extraction (UAE) protocols, ethanol/aqueous mixtures. The selectivity of catechin extraction was also depended on the type of the tissue (flesh, peel or pomace) and apple variety (green or red).

The cavitation phenomenon generated by ultrasound could increase extraction of valuable components from fruit peels by damaging cell membranes of samples and accelerating heat and mass transfer by disrupted cell walls of samples. Meanwhile, the gas water solvents could enhance the extraction efficiency of polyphenols and antioxidant activity from apple peels by enhancing cavitation phenomenon generated by ultrasound.

The efficiency of polyphenols purification from apple peel extracts with adsorption/desorption process by ultrasound treatment with the polyaromatic amberlite adsorbent XAD-16 and with membrane electro-filtration were studied. The obtained data demonstrated that the sonication significantly facilitated adsorption kinetics and increased activation energy of polyphenols adsorption. In addition, the desorption ratio was positively affected by the sonication during the adsorption step. On the other hand, the results demonstrated that the membrane electro-filtration allowed the purification of polyphenols in the anode (+) space and obtaining larger volume of filtrates.

I would first like to thank the China Scholarship Council (CSC) for been granted and allowed me to perform this work in good conditions. I would like to thank all those who, at different levels, contributed to the realization of this thesis.

I express my deepest gratitude to my supervisor Professor Eugène VOROBIEV for offering me this thesis subject, suggesting the research plan and correcting every article that I published. I thank him for sharing and communicating to me his passion for research, and having advised me, encouraged, supported with an availability of every moment.

I would like to thank my co-supervisor, the teacher Nadia BOUSSETTA for to have helped me during the realization of this thesis. She has participated in the whole of my thesis work, acting as an interpreter, a co-co-supervisor, and also a nice friend.

I express my gratitude to Professor Nikolai LEBOVKA for teaching me the enthusiasm of scientific research and an effective working methodology. I am very happy to express to him my deep grateful for the help and advice he gave me for this work and publishing articles.

I would like to thank Professor DIMITROV Krasimir, Professor ALLAF Karim, Professor DING Luhui and Doctor LOGINOV Maksym who did me the honor to judge this thesis. The advice they have given me will undoubtedly improve the quality of this thesis and help me in my future work.

I would also like to thank all the members of our team and especially those who have contributed directly or indirectly by their help or support to the good progress of this thesis: GRIMI Nabil, BALS Olivier, KOUBAA Mohamed, DAUZAT Bruno, LECLERC Hervé, LEFEBVRE Michaël, Zhichao Shi, EL KANTAR Sally, Caiyun Liu, Yantao Wang, Peng Du, Jinghua Xiao, Deyang Zhao, HEBERT Mathieu, CHADNI Morad, EL DACCACHE Marina, Congcong Ma, Rui Zhang, Dian Wang, Wenshuai Bai, Maiqi Xiang, Jishuai Li, Guoqiang Wei, Kaidi Peng…. I will not forget to thank all my Chinese friends with whom I shared the pleasures and the inconvenience of the life. Their unwavering support and encouragement have been indispensable to me during these years. All the great moments we have spent together in the city of Compiègne will be unforgettable memories for me.

Finally I would like to thank with all my heart my parents who were far physically but who was practically at my side every day to support me, without whom I would probably not have become what I am today. I thank them for their love unconditional, for always encouraging me to continue my studies throughout these years.

I would also like to thank my dear husband Jianhua Fan for supporting and accompanying me in these years without your support and love I could never finish my thesis and have a perfect memory in France.

Résumé

Cette thèse porte sur l'intensification de l'extraction de polyphénols à partir de produits à base de pomme (chair, peau et marc) par ultrasons (US) et sur la purification d'extraits de peau de pomme par adsorption/désorption et technologie membranaire.

L'extraction sélective des polyphénols issus des produits de la pomme a été analysée. Les données obtenues ont démontré la possibilité d'une régulation fine de l'extraction sélective de la matière soluble, de la catéchine et des composés polyphénoliques totaux en utilisant différentes températures, protocoles UAE, mélanges éthanol/aqueux. La sélectivité de l'extraction de la catéchine dépendait également du type de tissu (chair, peau ou marc) et de la variété de pomme (verte ou rouge).

Le phénomène de cavitation généré par les ultrasons pourrait augmenter l'extraction de composants précieux des pelures de fruits en endommageant les membranes cellulaires des échantillons et en accélérant ainsi le transfert de chaleur et de masse. D'autre part, les solvants eau-gaz pourraient améliorer l'efficacité d'extraction des polyphénols des peaux de pomme en renforçant le phénomène de cavitation généré par les ultrasons.

L'efficacité de la purification de polyphénols d'extraits de pelure de pomme par adsorption/désorption assisté par ultrasons (adsorbant polyaromatique Amberlite XAD-16) et par électrofiltration sur membrane a été mise en évidence. Les données obtenues ont démontré que la sonication facilitait significativement la cinétique d'adsorption, la capacité d'adsorption accrue et augmentation de l'énergie d'activation de l'adsorption des polyphénols. En outre, le taux de désorption a été positivement affecté par la sonication au cours de l'étape d'adsorption.

Par ailleurs, les résultats ont montré que l'électrofiltration sur membrane permettait de purifier les polyphénols dans l'espace anodique (+) et d'obtenir un volume plus important de filtrats.

Mots-clés : peau de pomme, polyphénols, ultrasons, extraction sélective, endommagement cellulaires, adsorption / désorption, membrane filtration II.3.2.2 pH ..................................................................................................................... II.3.2.3 Electrical conductivity ...................................................................................... II.3.2.4 Water holding capacity ..................................................................................... II.3.2.5 Particle size distribution ................................................................................... II.3.2.6 Hardness ........................................................................................................... II.3.2.7 Thickness .......................................................................................................... II.3.2.8 Color ................................................................................................................. II.3.2.9 Turbidity ........................................................................................................... II.3.2.10 Scanning electron microscopy ........................................................................ II.3.2.11 Fourier transform infrared spectroscopy ....................................................... II.3.2.12 Optical images ................................................................................................ II.3.2.13 Total polyphenol content ................................................................................ II.3.2.14 Catechin content ............................................................................................. II.3.2.15 Total flavonoid content ................................................................................... II.3.2.16 Proanthocyanidins content ............................................................................. II.3.2.17 Antioxidant activity ......................................................................................... II.3.2.18 Hydrogen peroxide content ............................................................................ II.3.2.19

II.3 Physico

Nomenclature and Abbreviations

Nomenclature

General Introduction

Apples contain various nutrients beneficial to human health with strong anti-inflammatory effects and high ability to prevent chronic diseases, especially polyphenols (flavanols, flavonols, phloridzin, procyanidin, chlorogenic acid, anthocyanin). Content of phenolics in apple pomace (peels, mesh, seeds, cores and stems) is much higher than in the juice or flesh of apples. Nowadays the extraction and purification of phenolic compounds from apple pomace, especially apple peels, attracts a great attention. US treatment generates air bubbles that propagate in the liquid medium with expansion and compression cycles. UAE is mainly based on acoustic cavitation and its hydrodynamic shear forces. The generated cavitation phenomenon from bubble collision can accelerate heat and mass transfer by plant cell walls disruption, leading to improved release of the target compounds from samples. In addition, the generated oxidative energy of radicals created during sonolysis of the solvent can result in a high extractive power of ultrasounds. Therefore, US treatment is beneficial to intensify extraction of polyphenols from material samples.

The conventional techniques for polyphenols purification of extracts are adsorption, chromatography-based techniques, nanofiltration (NF), and electrodialysis (ED). These purification techniques could be applied not only in laboratory but also in industry. Among these techniques, adsorption/desorption on the poly-aromatic amberlite adsorbent and membrane filtration can offer more effective and cleaner technologies for the separation and clarification of extracts due to their flexibility and operating conditions respectful of the environment. The major problem for adsorption/desorption with macroporous resin is low recovery rate and long purification time. For membrane filtration technique, it is the rapid decrease in permeate flow following clogging of the membrane. Hence the adsorption/desorption procedure assisted by sonication and membrane electro-filtration will be used for the selective purification of polyphenols from apple peels. This thesis aims to intensify the extraction of polyphenols from apple products by ultrasound treatment. Previous works were mainly focused on the impact of US on the improvement of aqueous extraction of solutes in general. Here, the focus will be done on the selective extraction of polyphenols from apple products and the effect of cavitation phenomenon produced by ultrasound on polyphenol extraction. On the other hand, purification polyphenols from apple peel extracts will also be studied. The application of adsorption/desorption procedure assisted by sonication and membrane electro-filtration for selective purification of polyphenols compared with proteins in extracts will be discussed. This thesis consists of five chapters.

The Chapter I presents the research status on the apple polyphenols, their different extraction processes, and new techniques for improving extraction that can be applied. Then the bibliographic study also focuses on describing current knowledge concerning the purification and separation of polyphenols from apple extracts.

The Chapter II describes materials and methods used in this study, by presenting the raw materials, the experimental devices, the different applied processes as well as physicochemical analyses and data calculation methods.

The Chapter III represents the results on the intensification of solute and polyphenols extraction from apple products (flesh, peel and pomace) with US pre-treatment, ethanol/water mixtures, and combined US and conventional heating. On the other hand the effects of CE and UAE protocols, and ethanol concentration on selectivity of polyphenols extraction from apple products will be presented.

The Chapter IV first focuses on the cavitation phenomenon produced by ultrasound leading to polyphenol extraction enhancement. On the other hand, the effect of cell damage and CO 2 concentration in gas water solvents on UAE of valuable components from apple peels will be analyzed.

The Chapter V discusses the application of adsorption/desorption procedure assisted by sonication for purification of polyphenols from apple peel extracts, and studies the selective purification of polyphenols from apple peels with membrane electro-filtration.

Finally, the general conclusions of this thesis will be summarized and some suggestions and perspectives for further work will be presented.

Chapter I Bibliography

This chapter 1 will introduce the apple products (flesh, peel and pomace), the polyphenols content, the conventional extraction technologies and the new extraction techniques. In addition, an analysis of the literature on existing polyphenols purification processes will be presented.

I.1 By-products of the apple industry

I.1.1 Apple pomace and apple peels

Typical by-products of the apple industry are illustrated in Fig. I.1 [START_REF] Perussello | Valorization of apple pomace by extraction of valuable compounds[END_REF][START_REF] Rabetafika | Fractionation of apple by-products as source of new ingredients: Current situation and perspectives[END_REF]. After the harvested apples are picked, they are washed and transported to the processing facilities. The apples are then pressed and juiced right away. Depending on the companies and end products, the apples will be processed in different ways before pressing. The fresh apple pomace and apple peels are produced at the same time with the raw apple juice.

Figure I.1. Conventional apple processing by products

During the processing of apple fruits for juice, cider, syrup or vinegar preparation, large amounts of solid residues (peel, core, seed, calyx, stem, and soft tissue) are generated [START_REF] Kennedy | Apple pomace and products derived from apple pomace: uses, composition and analysis[END_REF], among them apple pomace accounts for approximately 25-30% of the weight of the fresh apple [START_REF] Gullón | Evaluation of apple pomace as a raw material for alternative applications in food industries[END_REF]. Apple pomace mainly contains about 54% flesh, 34% peel, 7% seeds, 4% seed core and 2% stem [START_REF] Kolodziejczyk | Apple pomace as a potential source of nutraceutical products[END_REF]. Therefore, apple peel is the most main component in the apple pomace except underused apple flesh.

In addition, apple peels account for 13% of the weight of the fresh apple fruit [START_REF] Tarazona-Díaz | Assessment of by-products from fresh-cut products for reuse as bioactive compounds[END_REF]. Their by-products are obtained from apple sauce, canned apple manufacture, dried apple manufacture and fresh-cut apple [START_REF] Md | Potential utilization of fruit and vegetable wastes for food through drying or extraction techniques[END_REF][START_REF] Tian | Analysis of components and study on antioxidant and antimicrobial activities of oil in apple seeds[END_REF].

It is estimated that approximately 9000 metrics tons of apple peels are generated annually in Chile, as a result of apple processing [START_REF] Henríquez | Development of an ingredient containing apple peel, as a source of polyphenols and dietary fiber[END_REF].

I.1.2 Apple peels valorisations

At present, apple peels are typically used for non-valuable purposes with direct use including livestock feed, fertilizer, compost, press aid in the production of juice or vinegar and pressed into a cake. In addition, apple peels have began to be used as a source of pectin and fiber (Wolfe and Liu, 2003). The most common applications for apple peels are summarized in Table I.1 (Miceli-Garcia, 2014). [START_REF] Gassara | Pomace waste management scenarios in Qu{é}bec-Impact on greenhouse gas emissions[END_REF][START_REF] Masoodi | Use of apple pomace as a source of dietary fiber in cakes[END_REF][START_REF] Roberts | Utilization of dried apple pomace as a press aid to improve the quality of strawberry, raspberry, and blueberry juices[END_REF][START_REF] Singh | Studies on the rumen degradation kinetics and utilization of apple pomace[END_REF]) Extraction of bioactive compounds Dietary fibers, antioxidants, pectin, oil. [START_REF] Figuerola | Fibre concentrates from apple pomace and citrus peel as potential fibre sources for food enrichment[END_REF][START_REF] Schieber | A new process for the combined recovery of pectin and phenolic compounds from apple pomace[END_REF][START_REF] Tian | Analysis of components and study on antioxidant and antimicrobial activities of oil in apple seeds[END_REF][START_REF] Wijngaard | The optimization of extraction of antioxidants from apple pomace by pressurized liquids[END_REF] Products obtained via fermentation Organic acids, ethanol, aroma compounds, pigments, protein enriched animal feed, enzymes, heteropolysaccharides, baker's yeast. [START_REF] Attri | Optimization of apple pomace based medium and fermentation conditions for pigment production by Micrococcus species[END_REF]Berovič and Ostroveršnik, 1997;[START_REF] Bhushan | Baker's yeast production under fed batch culture from apple pomace[END_REF][START_REF] Hang | Apple pomace: A potential substrate for citric acid production by Aspergillus niger[END_REF][START_REF] Joshi | Preparation and evaluation of an animal feed byproduct produced by solid-state fermentation of apple pomace[END_REF][START_REF] Longo | Production of food aroma compounds: microbial and enzymatic methodologies[END_REF][START_REF] Stredansky | Xanthan production by solid state fermentation[END_REF][START_REF] Villas-Bôas | Bioconversion of apple pomace into a nutritionally enriched substrate by Candida utilis and Pleurotus ostreatus[END_REF] Fuel production Biogas, ethanol [START_REF] Hang | Production of fuels and chemicals from apple pomace[END_REF][START_REF] Jewell | Apple pomace energy and solids recovery[END_REF]) Substrate for edible mushrooms Shiitake and oyster mushroom [START_REF] Worrall | Shiitake and oyster mushroom production on apple pomace and sawdust[END_REF] Previous studies have demonstrated that apple peels contain a number of nutrient contents, such as phenolics, ascorbate, dietary fibers, and minerals [START_REF] Łata | Apple peel as a contributor to whole fruit quantity of potentially healthful bioactive compounds. Cultivar and year implication[END_REF][START_REF] Md | Potential utilization of fruit and vegetable wastes for food through drying or extraction techniques[END_REF]. For example, apple peels have higher antioxidant activities (such as antioxidant concentration and antioxidant capacity) and higher health-promoting properties (such as greater inhibitory effects on cancer cells) than the apple flesh or whole apple [START_REF] Drogoudi | Peel and flesh antioxidant content and harvest quality characteristics of seven apple cultivars[END_REF][START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF]Wolfe et al., 2003). In addition, several studies have reported that the dietary fibers and the minerals content are much higher in apple peels as compared to other edible parts of apples [START_REF] Gorinstein | Comparative contents of dietary fiber, total phenolics, and minerals in persimmons and apples[END_REF][START_REF] Henríquez | Development of an ingredient containing apple peel, as a source of polyphenols and dietary fiber[END_REF][START_REF] Leong | Apple and pear peel and pulp and their influence on plasma lipids and antioxidant potentials in rats fed cholesterol-containing diets[END_REF]. Moreover, it is known that the concentration of total polyphenol contents is much greater in the peel than in the flesh of apples [START_REF] Burda | Phenolic compounds and their changes in apples during maturation and cold storage[END_REF][START_REF] Ju | Relationships among simple phenol, flavonoid and anthocyanin in apple fruit peel at harvest and scald susceptibility[END_REF]. Previous studies had shown that the content of phenolic compounds in apple peels is higher than in apple flesh. The apple peels contain caffeic acid, catechins, chlorogenic acid, phloridzin, phloretin glycosides, and procyanidins as apple flesh. In addition, apple peel contains additional flavonoids not found in apple flesh, such as quercetin and cyanidin glycosides [START_REF] Escarpa | High-performance liquid chromatography with diodearray detection for the determination of phenolic compounds in peel and pulp from different apple varieties[END_REF][START_REF] Van Der Sluis | Activity and concentration of polyphenolic antioxidants in apple juice. 3. Stability during storage[END_REF]. Recycling of apple peels have been used as a source of phenolic compounds and dietary fibre in previous studies depending on different valuable compounds and different peel waste-derived materials (Table I.2). Since it is worth recovering these nutrients and developing value added products. Apple peels can be used in various food products to add phytochemicals and promote good health [START_REF] Md | Potential utilization of fruit and vegetable wastes for food through drying or extraction techniques[END_REF].

I.2 Polyphenols in apple peels

I.2.1 Introduction

Polyphenol is one of high value products of apple pomace, especially apple peels [START_REF] Kennedy | Apple pomace and products derived from apple pomace: uses, composition and analysis[END_REF]. Many studies were focused on the distribution of polyphenolic compounds in apple peels from different varieties and in comparison with different apple ingredients (flesh, whole apple or juice), the identification of polyphenolic components, and in specific cases the resulting concentration (Table I.3). The contents and composition of polyphenols can be rather different in dependence of the plant variety, environmental and post-harvest factors and the plant part (flesh, peels, seeds and pomace) [START_REF] Heimler | Plant polyphenol content, soil fertilization and agricultural management: a review[END_REF][START_REF] Oszmiański | Determination of phytochemical composition and antioxidant capacity of 22 old apple cultivars grown in Poland[END_REF]. The differences between polyphenols of peel and flesh from distinct varieties of apples were compared [START_REF] Kalinowska | Apples: content of phenolic compounds vs. variety, part of apple and cultivation model, extraction of phenolic compounds, biological properties[END_REF][START_REF] Mcrae | Comparison of the polyphenol profiles of apple fruit cultivars by correspondence analysis[END_REF][START_REF] Pérez-Ilzarbe | Phenolic compounds in apples: varietal differences[END_REF]. The authors confirmed the presence of flavonols and their glycosides in the peel of apples, while this compound was trace amounts in the flesh. The polyphenolic profiles and contents in peels and flesh from eight apple varieties were detected and compared [START_REF] Tsao | Polyphenolic profiles in eight apple cultivars using high-performance liquid chromatography (HPLC)[END_REF]. [START_REF] Lamperi | Polyphenol levels and free radical scavenging activities of four apple cultivars from integrated and organic farming in different Italian areas[END_REF] compared the polyphenols content from peels and flesh respectively of three red apple cultivars from Italy (Annurca, Red Chief and Staynam Neepling). In addition, the total polyphenol content (TPC) from peels and flesh for different varieties apples were compared. The TPC for Fuji apples and organic Golden Delicious apples were corresponding to 577.9 ± 8.99 mg/100g FW for peels and 140.9 ± 198 mg/100g FW for flesh, and 1204 ± 76.2 mg/kg -1 FW for peels and 241 ± 30.2 mg/kg -1 FW for flesh, respectively. Moreover, catechins, procyanidins, hydroxycinnamic acids, flavonol glycosides, dihydrochalcone glycosides and cyanidin-3-O-galactoside could be identified both in the apple peels and flesh. Especially, procyanidins, catechins and flavonols were the main constituents of apple peels [START_REF] Giomaro | Polyphenols profile and antioxidant activity of skin and pulp of a rare apple from Marche region (Italy)[END_REF]. Similar, previous researches have demonstrated that the total content of anthocyanins in apple peels was much higher than in apple flesh for different varieties of apples [START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF][START_REF] Tsao | Polyphenolic profiles in eight apple cultivars using high-performance liquid chromatography (HPLC)[END_REF].

Table I.3. The content of polyphenolic components in apple peels

Polyphenolic components Apple variety Content References

Chlorogenic acid 2-18 0.03-24 mg/g DM (Awad et al., 2000;Awad and de Jager, 2000;[START_REF] Łata | Cultivar variation in apple peel and whole fruit phenolic composition[END_REF] 1-4 0.6-44 mg/kg FW [START_REF] Duda-Chodak | Antioxidant activity of apples--an impact of maturity stage and fruit part[END_REF][START_REF] Escarpa | High-performance liquid chromatography with diodearray detection for the determination of phenolic compounds in peel and pulp from different apple varieties[END_REF][START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF][START_REF] Veberic | Phenolic compounds in some apple (Malus domestica Borkh) cultivars of organic and integrated production[END_REF] p-Coumaroylquinic acid 2 0.003-66.9 mg/g FW [START_REF] Guyot | Procyanidins are the most abundant polyphenols in dessert apples at maturity[END_REF][START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF] 1 0.05-0.19 mg/g DM [START_REF] Renard | Concentrations and characteristics of procyanidins and other phenolics in apples during fruit growth[END_REF] (+) Catechin 1-18 0.99-4.42 mg/g DM (Awad et al., 2000;[START_REF] Łata | Cultivar variation in apple peel and whole fruit phenolic composition[END_REF] 2-4 0.008-50.5 mg/g FW [START_REF] Escarpa | High-performance liquid chromatography with diodearray detection for the determination of phenolic compounds in peel and pulp from different apple varieties[END_REF][START_REF] Guyot | Procyanidins are the most abundant polyphenols in dessert apples at maturity[END_REF][START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF] (-) Epicatechin 18 1.24-5.75 mg/g DM (Łata et al., 2009) 1-4 0.036-2.589 mg/g FW [START_REF] Choi | Antioxidant properties of natural polyphenols and their therapeutic potentials for Alzheimer's disease[END_REF][START_REF] Escarpa | High-performance liquid chromatography with diodearray detection for the determination of phenolic compounds in peel and pulp from different apple varieties[END_REF][START_REF] Guyot | Procyanidins are the most abundant polyphenols in dessert apples at maturity[END_REF][START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF][START_REF] Veberic | Phenolic compounds in some apple (Malus domestica Borkh) cultivars of organic and integrated production[END_REF] Procyanidin B2 2-7 0.069-2.772 mg/g FW [START_REF] Escarpa | High-performance liquid chromatography with diodearray detection for the determination of phenolic compounds in peel and pulp from different apple varieties[END_REF][START_REF] Guyot | Procyanidins are the most abundant polyphenols in dessert apples at maturity[END_REF][START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF][START_REF] Kolodziejczyk | Apple pomace as a potential source of nutraceutical products[END_REF] Procyanidin B1 2-7 0.014-1.551 mg/g FW [START_REF] Escarpa | High-performance liquid chromatography with diodearray detection for the determination of phenolic compounds in peel and pulp from different apple varieties[END_REF][START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF][START_REF] Kolodziejczyk | Apple pomace as a potential source of nutraceutical products[END_REF]) Procyanidin C1 7 97-213 mg/kg FW [START_REF] Kolodziejczyk | Apple pomace as a potential source of nutraceutical products[END_REF] Phloridzin 2-13 0.46-18 mg/g DM [START_REF] Awad | Flavonoid and chlorogenic acid changes in skin of "Elstar"and "Jonagold"apples during development and ripening[END_REF](Awad et al., , 2000;;Awad and de Jager, 2000;[START_REF] Łata | Cultivar variation in apple peel and whole fruit phenolic composition[END_REF] 1-4 0.013-15.9 mg/g FW [START_REF] Choi | Antioxidant properties of natural polyphenols and their therapeutic potentials for Alzheimer's disease[END_REF][START_REF] Escarpa | High-performance liquid chromatography with diodearray detection for the determination of phenolic compounds in peel and pulp from different apple varieties[END_REF][START_REF] Guyot | Procyanidins are the most abundant polyphenols in dessert apples at maturity[END_REF][START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF][START_REF] Veberic | Phenolic compounds in some apple (Malus domestica Borkh) cultivars of organic and integrated production[END_REF] Quercetin-3-rhamnoside 1-3 0.131-95.1mg/g FW [START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF][START_REF] Veberic | Phenolic compounds in some apple (Malus domestica Borkh) cultivars of organic and integrated production[END_REF] 1 0.58-2.66 mg/g DM (Awad et al., 2000;[START_REF] Choi | Antioxidant properties of natural polyphenols and their therapeutic potentials for Alzheimer's disease[END_REF] Total phenolic compounds 1-4 0.172-3.050 mg /g DM [START_REF] Huber | Phenolic profiles and antioxidant properties of apple skin extracts[END_REF][START_REF] Vieira | Phenolic compounds and antioxidant activity of the apple flesh and peel of eleven cultivars grown in Brazil[END_REF] 1-2 1.407-215.4 mg/g FW [START_REF] Duda-Chodak | Antioxidant activity of apples--an impact of maturity stage and fruit part[END_REF][START_REF] Guyot | Procyanidins are the most abundant polyphenols in dessert apples at maturity[END_REF][START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF] Total Procyanidins 1-2 1.282-61.95 mg/g FW [START_REF] Guyot | Procyanidins are the most abundant polyphenols in dessert apples at maturity[END_REF][START_REF] Khanizadeh | Polyphenol composition and total antioxidant capacity of selected apple genotypes for processing[END_REF] Total Flavonoids 1-2 0.568-14.66 mg/g DM [START_REF] Awad | Flavonoid and chlorogenic acid changes in skin of "Elstar"and "Jonagold"apples during development and ripening[END_REF]Awad and de Jager, 2000;[START_REF] Vieira | Phenolic compounds and antioxidant activity of the apple flesh and peel of eleven cultivars grown in Brazil[END_REF] DM: dry matter, FW: fresh weight.

I.2.2 Polyphenols varieties

Five major groups of polyphenolic compounds are found in apple: anthocyanins, dihydrochalcones, flavan-3-ols/procyanidins (flavanols), flavonols and hydroxycinnamic acids [START_REF] Mazza | Anthocyanins and other phenolic compounds in fruits of red-flesh apples[END_REF][START_REF] Pérez-Ilzarbe | Phenolic compounds in apples: varietal differences[END_REF][START_REF] Schieber | A new process for the combined recovery of pectin and phenolic compounds from apple pomace[END_REF]. Among these polyphenolic compounds, many of them are often associated with sugar moieties [START_REF] Merken | Measurement of food flavonoids by high-performance liquid chromatography: a review[END_REF][START_REF] Tsao | Polyphenolic profiles in eight apple cultivars using high-performance liquid chromatography (HPLC)[END_REF]. Catechin, epicatechin, chlorogenic acid, cyanidin 3-glycosides, phloridzin, phloretin and quercetin 3-glycosides are the major individual polyphenolics in apples [START_REF] Awad | Flavonoid and chlorogenic acid changes in skin of "Elstar"and "Jonagold"apples during development and ripening[END_REF](Awad et al., , 2000)). These polyphenolic compounds, located in the plastids/vacuoles of the cell, are related to the physical characteristics of apples such as the color of the peel (green, red and yellow), the flavor of the flesh and therefore to the differences between different varieties of apples [START_REF] Petkovska | Comparison of different extraction solvents for assay of the polyphenol content in the peel and pulp of 21 apple cultivars from Macedonia[END_REF].

The flesh and the peel of the apples showed a different type and distribution of phenolics compounds. The dihydroxycinnamic acids (caffeic acid, chlorogenic acid and neochlorogenic acid), hydroxybenzoic acids (gallic acid), monomeric flavanols (catechins and epicatechins), oligomeric flavanols (procyanidins) and dihydrochalcones (phloridizin and phloretin glycosides) were found in both flesh and peel, whereas flavanol (quercetin glycosides) and anthocyanins (cyanidin 3-galacoside) were exclusively found in the peel [START_REF] Giomaro | Polyphenols profile and antioxidant activity of skin and pulp of a rare apple from Marche region (Italy)[END_REF]Kalinowska et al., 2014) (Fig.I.2.). In apple peels, the predominant group of polyphenolics was the procyanidins, followed by quercetin glycosides (Fig. I.3), which was similar with previous studies (Table .I.3). Especially, flavonoids (hydroxycinnamic acids) composed 90%

of the total polyphenolics in the peel [START_REF] Amiot | Phenolic composition and browning susceptibility of various apple cultivars at maturity[END_REF]. Content of total polyphenol compounds is much larger in the peel than in the flesh of the apples [START_REF] Burda | Phenolic compounds and their changes in apples during maturation and cold storage[END_REF][START_REF] Escarpa | High-performance liquid chromatography with diodearray detection for the determination of phenolic compounds in peel and pulp from different apple varieties[END_REF][START_REF] Ju | Relationships among simple phenol, flavonoid and anthocyanin in apple fruit peel at harvest and scald susceptibility[END_REF], especially procyanidins, flavonols and dihydrochalcone [START_REF] Francini | Phenolic compounds in apple (Malus x domestica Borkh.): compounds characterization and stability during postharvest and after processing[END_REF][START_REF] Bourvellec | Impact of noncovalent interactions between apple condensed tannins and cell walls on their transfer from fruit to juice: Studies in model suspensions and application[END_REF].

I.2.3 Polyphenols properties

I.2.3.1 Interaction with proteins, alkaloids and polysaccharides

Properties of polyphenols are greatly affected by their interactions with other constituents of the food. The astringency of polyphenols could be altered by the presence of various molecules, including polysaccharides and proteins [START_REF] Cheynier | Polyphenols in foods are more complex than often thought[END_REF][START_REF] El Gharras | Polyphenols: food sources, properties and applications--a review[END_REF]. The most important chemical characteristic of apple polyphenols is the binding reaction between polyphenols and proteins [START_REF] Cheynier | Polyphenols in foods are more complex than often thought[END_REF]. Interactions of polyphenols with proteins is responsible for astringency perception (resulting from interactions of tannins with salivary proteins), for the formation of haze and precipitates in beverages, and for inhibition of enzymes and reduced digestibility of dietary proteins (Fig. , 2012;[START_REF] Haslam | Polyphenol--protein interactions[END_REF]. The main reaction mechanism is that plant polyphenols first approach the surface of protein molecules through hydrophobic bonds, then polyphenol molecules enter hydrophobic bag, and subsequently multi-point hydrogen bond occurs. The complex molecular reactions of plant polyphenols with alkaloids, polysaccharides and even with biological macromolecules such as nucleic acids and cell membranes are similar to that reaction of polyphenols combing proteins [START_REF] De Freitas | Protein/polyphenol interactions: past and present contributions. Mechanisms of astringency perception[END_REF][START_REF] El Gharras | Polyphenols: food sources, properties and applications--a review[END_REF].

I.2.3.2 Complexation with metal ions

Many ortho-phenolic hydroxyl groups in plant polyphenols can be used as a kind of polyradical ligand to complexate with metal ions by forming stable five-membered ring chelates [START_REF] Dumur | Controlled spontaneous generation of gold nanoparticles assisted by dual reducing and capping agents[END_REF][START_REF] Rahim | Coordination-driven multistep assembly of metal--polyphenol films and capsules[END_REF]. Due to the multiple coordination groups, strong complexation ability and stability of polyphenols complex, most metal ions form precipitation after complexing with polyphenols (Slabbert, 1992) (presented in Fig. I.5).

Under alkaline conditions, polyphenols and metal ions can easily form multi-donor ligand [START_REF] Cherrak | In vitro antioxidant versus metal ion chelating properties of flavonoids: A structure-activity investigation[END_REF]. For polyphenols interacting with some high-valent metal ions, such as Cr 6+ and Fe 3+ , the metal ions are complexed and reduced from high-valence state to lowvalence state at the same time [START_REF] Zhu | Study on Complexation Reaction of Tea Infusion with Metal Ions[END_REF]. The pervious researches demonstrated that the complexation of polyphenols with metal ions was the chemical basis of many applications [START_REF] Castaneda-Ovando | Chemical studies of anthocyanins: A review[END_REF][START_REF] Mcdonald | Precipitation of metal ions by plant polyphenols: optimal conditions and origin of precipitation[END_REF].

Figure I.5. Schema of the complexation between quercetin and metal ions [START_REF] Kasprzak | Properties and applications of flavonoid metal complexes[END_REF].

I.2.3.3 Antioxidant and free radical scavenging ability

The O-phenolic hydroxyl group of plant polyphenols (catechol or pyrogallol) is easily oxidized into quinone structure, with consuming oxygen in the environment, and has a strong ability to capture free radicals such as reactive oxygen species, which makes polyphenols have strong antioxidant and free radical scavenging ability as following reaction (Rice-Evans, In apples, the contribution of anthocyanins to antioxidant activity was higher than the contribution of flavonols, flavan-3-ols and phenolic acids [START_REF] Jakobek | Phenolic compound composition and antioxidant activity of fruits of Rubus and Prunus species from Croatia[END_REF]. Authors concluded that the anthocyanins can be regarded as major phenolic antioxidants of apples.

The antioxidant activity was influenced by polyphenols content, and by the presence of stronger phenolic antioxidants (catechins, ellagic acid, and cyaniding-3-glucoside). In addition, plant polyphenols have strong ultraviolet (UV) absorption characteristics between 200 and 350 nm, especially in the high UV region with high energy and destructive power [START_REF] Chen | A green tea-derived polyphenol, epigallocatechin-3-gallate, inhibits I$κ$B kinase activation and IL-8 gene expression in respiratory epithelium[END_REF][START_REF] Pfeilschifter | Redox signaling in mesangial cells[END_REF]. Therefore, plant polyphenols can be used as effective ingredients of anti-ageing agents and sunscreen.

I.2.4 Polyphenols analysis

A variety of methods have been used to determine the polyphenols contents of foods.

Several spectrophotometric methods and some useful instrumental techniques involving separation include high-speed counter-current chromatography, supercritical fluid chromatography, gas chromatography, and capillary electrophoresis are used to quantify the total phenolic contents and individual classes of phenolic compounds [START_REF] Craft | Phenol-based antioxidants and the in vitro methods used for their assessment[END_REF][START_REF] Ignat | A critical review of methods for characterisation of polyphenolic compounds in fruits and vegetables[END_REF]. Among these approaches, the Folin-Ciocalteu analysis is widely used to determine the total phenolics [START_REF] Ignat | A critical review of methods for characterisation of polyphenolic compounds in fruits and vegetables[END_REF]. High performance liquid chromatography (HPLC) coupled with detection by absorbance, mass spectrometry or fluorimetry is one of the most frequently used method to quantify individual phenolics [START_REF] Corradini | Flavonoids: chemical properties and analytical methodologies of identification and quantitation in foods and plants[END_REF][START_REF] Pyrzynska | Recent developments in the HPLC separation of phenolic food compounds[END_REF]. In recent years, the fluorescence spectrum has been used to determine minor components in complex food samples, especially for polyphenols.

I.2.4.1 Folin-Ciocalteu analysis

The spectrophotometric method is widely used to determine total polyphenols content.

Folin-Ciocalteu method became the most frequently prescribed reagent and the most suitable reagent for spectrophotometric estimation of total polyphenols (González-San José and Diez, 1992; [START_REF] Kanner | Natural antioxidants in grapes and wines[END_REF][START_REF] Swain | The quantitative analysis of phenolic compound[END_REF]. The total polyphenols content is measured by the Folin-Ciocalteu method based on a colorimetric oxidation/reduction reaction of phenols [START_REF] Singleton | [END_REF]. 0. [START_REF] Candrawinata | Optimisation of the phenolic content and antioxidant activity of apple pomace aqueous extracts[END_REF]. The total polyphenol content ranged from 832.5 to 1257.6 µg GAE/g detecting with Folin-Ciocalteu colorimetric method. The comparative evaluation of bio-solvents for the efficient extraction of polyphenolic phytochemicals of apple waste peels was studied by [START_REF] Blidi | A comparative evaluation of bio-solvents for the efficient extraction of polyphenolic phytochemicals: apple waste peels as a case study[END_REF]. In this study, Folin-Ciocalteu colorimetric method was used to determinate the total polyphenol content (18.34-18.96 mg GAE/g DM). No matter in the past or at present, almost all the researchers use Folin-Ciocalteu colorimetric method as a standard method to determinate polyphenol content in the samples.

I.2.4.2 High Pressure Liquid Chromatography analysis

High pressure liquid chromatography (HPLC) is almost the most useful analytical technique for characterization of polyphenolic compounds, which is preferred for the separation and quantification of polyphenols in samples [START_REF] Ignat | A critical review of methods for characterisation of polyphenolic compounds in fruits and vegetables[END_REF]. The chromatographic conditions of HPLC methods include the use of a reversed-phase C18 column, UV-Vis diode array detector, and a binary solvent system containing acidified water (solvent A) and a polar organic solvent (solvent B). The reversed phase columns could considerably enhance the HPLC separation of phenolic compounds. In addition, various supports and mobile phases are available for the analysis of different varieties of polyphenols such as flavanones, flavonols, flavones, flavan-3-ols, anthocyanins, procyanidins, procyanidins, and phenolic acids [START_REF] Naczk | Phenolics in cereals, fruits and vegetables: Occurrence, extraction and analysis[END_REF].

HPLC coupled to fluorimetric, diode array or mass detectors was the most employed technique to characterize and quantify phenolic compounds in food [START_REF] Albani | Fluorescence spectroscopy in food analysis[END_REF][START_REF] Fontana | High-throughput method based on quick, easy, cheap, effective, rugged and safe followed by liquid chromatography-multi-wavelength detection for the quantification of multiclass polyphenols in wines[END_REF][START_REF] Gonçalves | Development of a novel microextraction by packed sorbent-based approach followed by ultrahigh pressure liquid chromatography as a powerful technique for quantification phenolic constituents of biological interest in wines[END_REF]. HPLC method was used to investigate the profiles of polyphenolic compounds (various hydroxycinnamics, dihydrochalcones, procyanidins, flavonols and dihydrochalcones) in eight different apple varieties and different parts (peel and flesh) of apples [START_REF] Tsao | Polyphenolic profiles in eight apple cultivars using high-performance liquid chromatography (HPLC)[END_REF]. In addition, a solid-liquid extraction procedure followed by reversed-phase high-performance liquid chromatography (RP-HPLC) coupled with a photodiode array detector (DAD) for the determination of polyphenols (catechin, epicatechin, 5-caffeoylquinic acid, p-coumaric acid, phloridzin, hyperoside, isoquercitrin, rutin, quercitrin and ideain) from freeze-dried apple peel and flesh was reported [START_REF] Alonso-Salces | A validated solid--liquid extraction method for the HPLC determination of polyphenols in apple tissues: Comparison with pressurised liquid extraction[END_REF].

The HPLC technique was also used for the analyze of the major polyphenols (chlorogenic acid, caffeic acid, syrigin, procyanidin B2, (-)-epicatechin, cinnamic acid, coumaric acid, phlorizin and quercetin) from apple pomace and for the study of the optimal extraction conditions with microwave treatment [START_REF] Bai | Optimization of microwave-assisted extraction of polyphenols from apple pomace using response surface methodology and HPLC analysis[END_REF]. The phenolic composition from the unripe apple extracted by ultrasound (US) was determined by HPLC in Figure I.6 [START_REF] Yue | Ultrasound-assisted extraction, HPLC analysis, and antioxidant activity of polyphenols from unripe apple[END_REF]. The effect of processing conditions on polyphenols composition ((-)-epicatechin, procyanidin B2, chlorogenic acid, and procyanidin B1) from young apple was studied by HPLC. HPLC analysis method has been widely used for polyphenols analysis from apple solids and apple juice. Qualities of commercial apple juice/stored juice were also evaluated on the basis of the polyphenols content with HPLC analysis [START_REF] Gliszczynska-Swiglo | Quality of commercial apple juices evaluated on the basis of the polyphenol content and the TEAC antioxidant activity[END_REF]. Results presented that storage of juices resulted in a decrease of phenolic acids from 5% to 21%, and flavonoids from 8% to 19%. Apple juice produced by different apple cultivars was studied. 17 kinds of polyphenols were analyzed by HPLC analytical techniques, and the content of every polyphenol depends on the apple cultivars and processing method [START_REF] Kahle | Polyphenol profiles of apple juices[END_REF]. In addition, individual phenol (hydroxycinnamic acids 64.9%, flavonols 21.6% and dihydrochalcones 13.6%) of apple juice was quantified by HPLC-DAD analytical technique to reflect that UHPH treatment was useful to prevent degradation of polyphenols compounds (Suárez-Jacobo et al., 2011).

I.2.4.3 Fluorescence spectroscopy

Compared to other spectroscopic techniques, fluorescence spectroscopy is more sensitive and more selective. It significantly reduces spectral complexity and suppresses light-scattering interferences [START_REF] Andrade-Eiroa | Critical approach to synchronous spectrofluorimetry[END_REF]. Due to its unique advantages, fluorescence spectroscopy is especially useful for studies of minor components in complex food samples with the presence of interferences [START_REF] Christensen | Multivariate autofluorescence of intact food systems[END_REF]. Normally, fluorescence intensity is measured as a function of the simultaneously scanned emission and excitation wavelengths.

During the last decade, fluorescence spectroscopy has been widely used for polyphenols analysis of food materials [START_REF] Andersen | Autofluorescence spectroscopy in food analysis[END_REF][START_REF] Sádecká | Fluorescence spectroscopy and chemometrics in the food classification-a review[END_REF]. Especially, [START_REF] Merzlyak | Effect of anthocyanins, carotenoids, and flavonols on chlorophyll fluorescence excitation spectra in apple fruit: signature analysis, assessment, modelling, and relevance to photoprotection[END_REF] recorded apple samples' chlorophyll fluorescence excitation and diffuse reflection spectra in the visible and near UV regions to examine whole apple fruit differing in pigment content and composition. The authors identified the spectral bands sensitive to the pigment concentration and built linear models for non-destructive assessment of anthocyanins, carotenoids, and flavonols by using fluorescence spectroscopy. Nowadays, fluorescence spectroscopy has been more widely used to study apple juice than for apple tissue. The research demonstrated that the intensity of fluorescence spectra was correlated with the soluble solid contents of apple juice [START_REF] Seiden | Exploring fluorescence spectra of apple juice and their connection to quality parameters by chemometrics[END_REF]. Apple juice produced from different apple varieties could be classified with different techniques based on fluorescence spectroscopy [START_REF] Poryvkina | Evaluation of apple juice quality using spectral fluorescence signatures[END_REF]. In addition, the profile of fluorescence spectroscopy was correlated with formed substances during the thermal processing of apple juices. In addition, the analysis of fluorescence spectroscopy could be used for monitoring the nonenzymatic browning of juice [START_REF] Zhu | Evaluation of the non-enzymatic browning in thermally processed apple juice by front-face fluorescence spectroscopy[END_REF]. Recently, fluorescence spectra combined with parallel factor analysis (PARAFAC) was used to analyze varieties of polyphenols component from commercial apple juices with excitation/emission wavelengths at 270/315 nm, (310,370)/455 nm, 430/(550,680) nm [START_REF] Włodarska | Explorative study of apple juice fluorescence in relation to antioxidant properties[END_REF]. [START_REF] Włodarska | Screening of antioxidant properties of the apple juice using the front-face synchronous fluorescence References 207 and chemometrics[END_REF].

From large amounts of previous literatures analysis, the Folin-Ciocalteu method and HPLC method were the most widely used methods for quantitative and qualitative analysis of polyphenols of apple samples, respectively. The Folin-Ciocalteu method is simple, whereas it can only give an estimation of the total phenolic content. This is because the color reaction will occur with any oxidizable phenolic hydroxy group [START_REF] Gómez-Caravaca | Advances in the analysis of phenolic compounds in products derived from bees[END_REF]. The HPLC method is useful for the separation and quantification of polyphenolics in samples.

Nevertheless, HPLC methods present limitations in detection of complex samples due to the low sensitivity [START_REF] Ignat | A critical review of methods for characterisation of polyphenolic compounds in fruits and vegetables[END_REF]. Recently, fluorescence spectroscopy was a new determination method for specific polyphenols of apple samples because of good sensitivity and specificity (Porgal and B y ktuncel, 2012;[START_REF] Rodr Guez-Delgado | Separation of phenolic compounds by high-performance liquid chromatography with absorbance and fluorimetric detection[END_REF].

I.2.5 Polyphenols applications

I.2.5.1 Food applications

I.2.5.1.1 Functional foods

Apple polyphenols can prevent hypertension and dental caries, resist tumor, senility, mutation, radiation and allergy, and enhance muscle strength with improvement of the activity of enzyme free radical scavenger (superoxidase dismutase, catalase and glutathioneperoxidase) in human body [START_REF] Padmini | Comparative study on composition and antioxidant properties of mint and black tea extract[END_REF]. Nowadays, apple polyphenols have be used in the development and production of functional foods [START_REF] Landete | Updated knowledge about polyphenols: functions, bioavailability, metabolism, and health[END_REF][START_REF] Lea | 26 Fruit Phenolics in Colon Cancer Prevention and Treatment[END_REF][START_REF] Terao | Dietary flavonoids as antioxidants[END_REF][START_REF] Wang | Health-promoting food ingredients and functional food processing[END_REF][START_REF] Watson | Bioactive foods and extracts: Cancer treatment and prevention[END_REF].

I.2.5.1.2 Meat products

Apple polyphenols are beneficial to prevent oxidation and deterioration of meat products.

The antioxidant property of apple polyphenols could improve the freshness of meat products and extend shelf life [START_REF] Beriain | Production of Aspergillus niger pectolytic enzymes by solid state bioprocessing of apple pomace[END_REF][START_REF] Velasco | Improving meat quality through natural antioxidants[END_REF][START_REF] Yu | Antioxidant effect of apple phenolic on lipid peroxidation in Chinese-style sausage[END_REF]. In addition, apple polyphenols could reduce the fishy smell with inhibiting the production of volatile trimethylamine [START_REF] Lakshmanan | Fish spoilage and quality assessment[END_REF]. Previous studies presented that apple polyphenols can significantly inhibit the oxidation of fat in meat and improve the stability of the red color of meat [START_REF] Luciano | Dietary tannins improve lamb meat colour stability[END_REF][START_REF] Rojas | Effect of natural antioxidants on oxidative stability of frozen, vacuum-packaged beef and pork[END_REF][START_REF] Xue-Ping | Study on the antioxidant activities of Apple Polyphenol in Preserved Meats[END_REF].

I.2.5.1.3 Wine and beverage

Apple polyphenols have been used as a clarifying agent for wine and beverage [START_REF] Chung | Stabilization of natural colors and nutraceuticals: Inhibition of anthocyanin degradation in model beverages using polyphenols[END_REF][START_REF] Shahidi | Phenolics and polyphenolics in foods, beverages and spices: Antioxidant activity and health effects--A review[END_REF]. The connection of the phenolic hydroxyl group and amide group in protein with hydrogen bond can precipitate the component forming with gelatin and tannin, and can remove other suspended solids [START_REF] Marchal | Use of enological additives for colloid and tartrate salt stabilization in white wines and for improvement of sparkling wine foaming properties[END_REF][START_REF] Siebert | Haze in beverages[END_REF][START_REF] Siebert | Haze formation in beverages[END_REF]. Adding apple polyphenols to the vitamin C solution can effectively inhibit the degradation of vitamin C and the fading of pigments, especially β-carotene [START_REF] Huvaere | Flavonoids protecting food and beverages against light[END_REF]. Previous studies have demonstrated that apple polyphenols (1%) can keep the color of beverage during the shelf life, especially for beverages containing β-carotene [START_REF] Chung | Stabilization of natural colors and nutraceuticals: Inhibition of anthocyanin degradation in model beverages using polyphenols[END_REF][START_REF] Shahidi | Phenolics and polyphenolics in foods, beverages and spices: Antioxidant activity and health effects--A review[END_REF][START_REF] Sun-Waterhouse | The development of fruit-based functional foods targeting the health and wellness market: a review[END_REF]. In addition, phloridzin and xylose-phloridzin have been widely used as the characteristic indexes of apple and its products to detect the mutual admixture of apple and pear products. At present, this detection method has played an important role in identifying product quality in international trade [START_REF] Górnaś | Phenolic compounds in different fruit parts of crab apple: Dihydrochalcones as promising quality markers of industrial apple pomace byproducts[END_REF][START_REF] Thavarajah | Adulteration of apple with pear juice: emphasis on major carbohydrates, proline, and arbutin[END_REF][START_REF] Versari | Adulteration of fruit juices: dihydrochalcones as quality markers for apple juice identification[END_REF].

I.2.5.1.4 Vegetables and fruits

Apple polyphenols had antibacterial effects, such as bacillus, escherichia coli, pseudomonas and other tested bacteria. Apple polyphenol extracts have good thermal stability in the bacteriostatic activity, especially under the condition of pH=5-6 and low concentration of inorganic salt (<0.3mol/L) [START_REF] Cai-Wen | Study on the Extraction of Total Flavonoids from Apple Pomace and Its Antibacterial Activity[END_REF][START_REF] Vivek | Anticariogenic activity of Lagerstroemia speciosa (L.)[END_REF]. Spraying lowconcentration apple polyphenol solution on fresh products is beneficial for the preservation and corrosion of fruits and vegetables by inhibiting bacterial reproduction and keeping the original color [START_REF] Akazome | Characteristics and physiological functions of polyphenols from apples[END_REF][START_REF] Marshall | Enzymatic browning in fruits, vegetables and seafoods[END_REF][START_REF] Zhang | Enzymatic browning and antioxidant activities in harvested litchi fruit as influenced by apple polyphenols[END_REF].

I.2.5.1.5 Bubble gum

Previous studies demonstrated that polyphenols, especially tea polyphenol, could effectively reduce the amount of methyl mercaptan produced and remove bacteria during chewing bubble gum [START_REF] Porciani | The effect of zinc acetate and magnolia bark extract added to chewing gum on volatile sulfur-containing compounds in the oral cavity[END_REF][START_REF] Tao | A randomized trial on the inhibitory effect of chewing gum containing tea polyphenol on caries[END_REF]. Especially, apple polyphenols can be added in bubble gum because of its good inhibition of halitosis.

In addition, apple polyphenols have been used as new additives in bread, cake, pastry and oil production [START_REF] Sudha | Apple pomace as a source of dietary fiber and polyphenols and its effect on the rheological characteristics and cake making[END_REF][START_REF] Yilmaz | Novel uses of catechins in foods[END_REF].

I.2.5.2 Cosmetics applications

Apple polyphenol is a kind of natural product with unique physiological and chemical activities, which has good convergence and adhesion [START_REF] Sugiyama | Oligomeric procyanidins in apple polyphenol are main active components for inhibition of pancreatic lipase and triglyceride absorption[END_REF][START_REF] Zillich | Polyphenols as active ingredients for cosmetic products[END_REF]. Apple polyphenols can maintain the synthesis of collagen, inhibit elastase, protect collagen and improve skin elasticity to avoid or reduce the generation of wrinkles and keep the appearance of delicate skin [START_REF] Gaudout | Phloridzin-rich phenolic fraction and use thereof as a cosmetic, dietary or nutraceutical agent[END_REF][START_REF] Gaudout | Use of a dihydrochalcone-rich phenolic fraction in a cosmetic treatment[END_REF][START_REF] Gaudout | Use of a dihydrochalcone-rich phenolic fraction in a cosmetic treatment[END_REF]. Apple polyphenol is often added as an active ingredient in cosmetics, playing an important role in anti-oxidation, anti-aging, anti-ultraviolet, anti-radiation, sunscreen, whitening and moisturizing [START_REF] Baldisserotto | Synthesis, antioxidant and antimicrobial activity of a new phloridzin derivative for dermo-cosmetic applications[END_REF][START_REF] Gaudout | Phloridzin-rich phenolic fraction and use thereof as a cosmetic, dietary or nutraceutical agent[END_REF]. Especially, condensed tannin extracted from apples can play an anti-allergic role with effectively inhibiting the dissociation of histamine and hyaluronidase activity [START_REF] Magrone | Influence of polyphenols on allergic immune reactions: mechanisms of action[END_REF]. In addition, apple polyphenols are used to prepare vitamin C or vitamin E and polyphenols complex whitening agents because of phenolics can inhibit the activity of tyrosinase and catalase and remove reactive oxygen species [START_REF] Shoji | Procyanidin trimers to pentamers fractionated from apple inhibit melanogenesis in B16 mouse melanoma cells[END_REF].

I.2.5.3 Other applications

Apple polyphenols have been used to formulate antibacterial edible films [START_REF] Alberto | Antimicrobial effect of polyphenols from apple skins on human bacterial pathogens[END_REF][START_REF] Du | Physical and antibacterial properties of edible films formulated with apple skin polyphenols[END_REF]. In addition, grafting apple polyphenols onto the polymer chain can not only reduce the environmental damage caused by phenolic waste discharged in the processing process, but also can be used as a product to treat wastewater containing heavy metal ions [START_REF] Celik | Removal of heavy metal ions from aqueous solutions via adsorption onto modified lignin from pulping wastes[END_REF][START_REF] Chand | Xanthate modified apple pomace as an adsorbent for removal of Cd (II), Ni (II) and Pb (II), and its application to real industrial wastewater[END_REF].

Based on above applications, apple polyphenols are nowadays becoming more and more important in both food industrial area and other non-food domains. Therefore, the intensification of phenolic compounds extraction from apple products (peels, seeds, flesh and pomace) begins to attract a great attention of many researchers (Ćetković et al., 2008).

I.3 Polyphenols extraction technologies

I.3.1 Conventional extraction

The conventional method of polyphenols recovery is based on a solid-liquid solvent extraction. Water, alcohols (methanol, ethanol, and alcohol-water mixtures), acetone, and ethyl acetate are commonly used for the extraction of polyphenols from apples [START_REF] Wijngaard | The optimization of extraction of antioxidants from apple pomace by pressurized liquids[END_REF]. Depending on the type of solvent used, the cell membranes could be more vulnerable which facilitates the release of polyphenols. Solid-liquid extraction is defined as a mass transport phenomenon in which solids contained in a solid matrix migrate into a solvent brought into contact with the matrix [START_REF] Ignat | A critical review of methods for characterisation of polyphenolic compounds in fruits and vegetables[END_REF]. Mass transport phenomena can be enhanced by changes in concentration gradients, diffusion coefficients or boundary layer [START_REF] Corrales | Extraction of anthocyanins from grape skins assisted by high hydrostatic pressure[END_REF]. The extraction efficiency is known to be a function of process conditions. The concentration of the polyphenol components in extracts is affected by some factors, including temperature, time, solid-liquid ratio, and flow rate [START_REF] Hayouni | The effects of solvents and extraction method on the phenolic contents and biological activities in vitro of Tunisian Quercus coccifera L. and Juniperus phoenicea L. fruit extracts[END_REF][START_REF] Pinelo | Extraction of antioxidant phenolics from almond hulls (Prunus amygdalus) and pine sawdust (Pinus pinaster)[END_REF][START_REF] Rubilar | Residuos agroindustriales como fuente de antioxidantes[END_REF]. Conventional extraction as heating, boiling, or refluxing can be used to extract natural phenolic compounds. But these conventional methods are time and energy consuming, and some methods even will take a few hours. Moreover, they involve extensive subsequent solid-liquid separation and purification steps.

I.3.2 Intensification of extraction process

Recently there has been an increasing demand for new extraction techniques that are environmentally friendly, faster, and more efficient than conventional extraction methods.

Among these techniques, pressurized fluid, supercritical fluid, microwave, high hydrostatic pressure, ultrasound (US), pulsed electric fields (PEF) and high voltage electrical discharges (HVED) have shown their efficiencies for the extraction of polyphenols from apple products (Table I.4). More difficult to a subsequent solid to liquid separation, damage both cell walls and cell membranes, difficult to scale-up [START_REF] Boussetta | Application of electrical treatments in alcoholic solvent for polyphenols extraction from grape seeds[END_REF][START_REF] Gros | Towards an alternative extraction process for linseed oil[END_REF]

I.3.2.1 Microwave

Microwave-assisted extraction is based on the direct effect on molecules by ionic conduction and dipole rotation [START_REF] Pérez | Microwave hydrodiffusion and gravity processing of Sargassum muticum[END_REF]. Microwave energy can heat the solvents in contact with solid samples and extract interest compounds from solid samples into solvents [START_REF] Garcia | Acceleration and automation of solid sample treatment[END_REF], by increasing the internal pressure inside the cells that subsequently facilitates the rupture of cellular walls and the release of active compounds to solvent (B. Zhang et al., 2008a). The electromagnetic waves caused by microwave can produce a synergistic combination of two transport phenomena: heat and mass gradients working in the same direction [START_REF] Chemat | Microwave assisted separations: green chemistry in action[END_REF] (Barba et al., 2015b;[START_REF] Camel | Microwave-assisted solvent extraction of environmental samples[END_REF]. Microwave treatment has been widely used to extract polyphenols from industrial apple pomace. Microwave-assisted extraction at optimal conditions (microwave power of 650.4 W, extraction time of 53.7 s, ethanol concentration of 62.1% and the ratio of solvent to raw material of 22.9:1) could get a higher extraction yield of TPC (62.68±0.35 mg GAE/100 g) with lower solvent consumption compared to the conventional extraction [START_REF] Bai | Optimization of microwave-assisted extraction of polyphenols from apple pomace using response surface methodology and HPLC analysis[END_REF]. Similar results have shown that higher yields of polyphenolic compounds from apple pomace could be extracted by the combination of microwave treatment and application of ethanolwater solvents [START_REF] Rezaei | Solvent and solvent to sample ratio as main parameters in the microwave-assisted extraction of polyphenolic compounds from apple pomace[END_REF]. In addition, the effects of US and microwave treatment on polyphenols extraction from apple pomace were compared [START_REF] Ajila | Solid-state fermentation of apple pomace using Phanerocheate chrysosporium--Liberation and extraction of phenolic antioxidants[END_REF] PEF treatment allowed selective extraction of different bio-molecules from apples (e.g. carbohydrates, proteins, pectin, pigments and flavors) [START_REF] Vorobiev | Enhanced extraction from solid foods and biosuspensions by pulsed electrical energy[END_REF].

Moreover, obtained data demonstrated that PEF pretreatment can significantly enhance extraction of polyphenols from apple flesh, peel, pomace and juice [START_REF] Lohani | Application of the pulsed electric field to release bound phenolics in sorghum flour and apple pomace[END_REF][START_REF] Turk | Improving apple juice expression and quality by pulsed electric field on an industrial scale[END_REF][START_REF] Vorobiev | Pulsed-electric-fields-induced effects in plant tissues: fundamental aspects and perspectives of applications[END_REF][START_REF] Wiktor | Acoustic emission as a tool to assess the changes induced by pulsed electric field in apple tissue[END_REF]. PEF combined with pressing could become a good alternative to traditional process for production of higher quality apple juices [START_REF] Grimi | Impact of apple processing modes on extracted juice quality: pressing assisted by pulsed electric fields[END_REF]. In addition, the effects of PEF treatment (E = 450 V/cm; t = 10 ms) and apple mash size on juice yield, polyphenolic compounds, sugars, and malic acid were studied [START_REF] Turk | Effect of pulsed electric fields treatment and mash size on extraction and composition of apple juices[END_REF]. Study results demonstrated that the yield (Y) of apple juice increased significantly after PEF treatment of large mash (Y = 71.4%) and of small mash (45.6%) combined with conventional press. For apple pomace, PEF treatment could successfully release the bound phenolics and enhance the total polyphenols content and antioxidant activity [START_REF] Lohani | Application of the pulsed electric field to release bound phenolics in sorghum flour and apple pomace[END_REF]. In addition, PEF pretreatment has been beneficial for preserving important properties (purity, color, texture, flavor and nutrients) of apples and these properties would be destroyed by traditional mechanical, thermal or chemical pretreatments [START_REF] Vorobiev | Enhanced extraction from solid foods and biosuspensions by pulsed electrical energy[END_REF].

Moreover, previous research found that PEF application to the whole apple in an aqueous medium can be sensitive to changes in electric field induced inside tissue and depends on the conductivity of the aqueous medium [START_REF] Grimi | Acoustic impulse response in apple tissues treated by pulsed electric field[END_REF].

I.3.2.3 High voltage electrical discharges

High voltage electrical discharges (HVED) introduce energy directly into an aqueous solution through a plasma channel formed by a high-current/high-voltage electrical discharge between two submerged electrodes. HVED includes a large range of current (10 3 -10 4 A), voltage (10 3 -10 4 V) and frequency (10 -2 -10 -3 Hz) [START_REF] Chang | Pulsed arc discharge in water: Mechanism of current conduction and pressure wave formations[END_REF], while requires short treatment time (a few ms), low energy consumptions (10-50 kJ/kg) and low temperature elevations (<5 °C) [START_REF] Gros | Towards an alternative extraction process for linseed oil[END_REF]. HVED results in several phenomena (such as thermal, photonic, acoustic and mechanical phenomena) that can appear separately or in combination.

The phenomena generated by HVED strongly depend on the environment in which they are applied: aqueous or gaseous medium [START_REF] Vorobiev | Enhanced extraction from solid foods and biosuspensions by pulsed electrical energy[END_REF]. It is widely believed that HVED produces two types of discharges in liquids: slow discharge (subsonic) and rapid discharge (supersonic). The shock waves and the cavitation bubbles produced by HVED can Nowadays, few researches have studied the application of HVED-assisted extraction from apple products. However, HVED has been widely applied to extract polyphenols from other food samples or wine products. Many researchers studied the optimal conditions for HVEDassisted extraction of polyphenols from food materials. At the optimal conditions, the intensification of the extraction of total polyphenols was different for various raw materials at both laboratory and pilot scales (Table I.5). [START_REF] Boussetta | Electrically assisted extraction of soluble matter from chardonnay grape skins for polyphenol recovery[END_REF]. HVED was applied for intensification of the extracted polyphenols from grape pomace [START_REF] Boussetta | Valorisation of grape pomace by the extraction of phenolic antioxidants: application of high voltage electrical discharges[END_REF]. The results demonstrated that when the electric energy input increased to 80 kJ/kg, both total polyphenols content and antioxidant activity significantly increased. In addition, the grape seeds treated by HVED were clearly fragmented at the optimal treatment conditions (total specific energy input of 160 kJ/kg, pressure shock wave higher than 100 bar) for both laboratory and pilot scales [START_REF] Boussetta | Application of electrical treatments in alcoholic solvent for polyphenols extraction from grape seeds[END_REF]. HVED-assisted extraction allowed an increase by 35% of TPC in comparison with a conventional extraction in the same conditions (pH = 2.5 and ethanol concentration of 50% in water) from grape stems [START_REF] Brianceau | High voltage electric discharges assisted extraction of phenolic compounds from grape stems: effect of processing parameters on flavan-3-ols, flavonols and stilbenes recovery[END_REF]. Polyphenols from flaxseed cake were also extracted by HVED [START_REF] Boussetta | Effect of high voltage electrical discharges, heating and ethanol concentration on the extraction of total polyphenols and lignans from flaxseed cake[END_REF]. The researchers studied the effects of HVED, mild temperature (20-60 °C) and ethanol addition in water (0-25%) on the extraction of polyphenols from the whole and crushed flaxseed cakes. The experiment results showed that HVED noticeably enhanced the aqueous and hydro-ethanolic extractions of polyphenols from both crushed and non crushed flaxseed cakes. In addition, the application of HVED increased significantly the aqueous and hydro-ethanolic extractions of total polyphenols, and proteins of the recovered extracts from olive kernels than the application of PEF and US (Roselló-Soto et al., 2015a). HVED pretreatment was efficient to enhance the extraction yields of reducing sugars (19 g/100 g DM) and polyphenols (0.7 g/100 g DM) from orange peels [START_REF] El Kantar | High voltage electrical discharges combined with enzymatic hydrolysis for extraction of polyphenols and fermentable sugars from orange peels[END_REF]. Nowadays, HVED has been regarded as an effective technique for disrupting sample tissues and improving the release of polyphenols.

I.3.2.4 Ultrasound

I.3.2.4.1 Introduction

Ultrasound (US) is composed of sound waves with frequency beyond the limit of human hearing. US technique is relatively low cost, simple and energy saving, and thus has been widely utilized in many food industrial fields, such as improving food quality during processing and storage, intensifying extraction, freezing and drying process [START_REF] Awad | Applications of ultrasound in analysis, processing and quality control of food: A review[END_REF]. Especially, US treatment is beneficial for the extraction of different kind of compounds from various fruits and vegetables (Chemat et al., 2017b[START_REF] Chemat | Applications of ultrasound in food technology: processing, preservation and extraction[END_REF], such as polyphenols [START_REF] Dimitrov | Modeling and Optimization of Extraction and Energy Consumption during Ultrasound-Assisted Extraction of Antioxidant Polyphenols from Pomegranate Peels[END_REF][START_REF] Wang | Selectivity of ultrasound-assisted aqueous extraction of valuable compounds from flesh and peel of apple tissues[END_REF], polysaccharides [START_REF] Chen | Optimization for ultrasound extraction of polysaccharides from mulberry fruits with antioxidant and hyperglycemic activity in vitro[END_REF][START_REF] Hromadkova | Ultrasonic extraction of plant materials---investigation of hemicellulose release from buckwheat hulls[END_REF] and esters [START_REF] Rodrigues | Optimization of the production of ethyl esters by ultrasound assisted reaction of soybean oil and ethanol[END_REF][START_REF] Wu | Ultrasound-assisted extraction of ginseng saponins from ginseng roots and cultured ginseng cells[END_REF].

I.3.2.4.2 Mechanisms of action

US treatment generates air bubbles that propagate in the liquid medium with expansion and compression cycles. A local pressure inside of air bubbles can attain 50 MPa and a local temperature up to 5000°C [START_REF] Mason | Ultrasound in synthetic organic chemistry[END_REF]. The cavitation phenomenon resulting from bubble collision is capable of damaging proximate cell membranes of samples [START_REF] Chemat | Comparison of conventional and ultrasound-assisted extraction of carvone and limonene from caraway seeds[END_REF].

The generated cavitational effects can accelerate heat and mass transfer by plant cell walls disruption, leading to improved release of the target compounds from several natural sources (Roselló-Soto et al., 2015b). In addition, there is also the oxidative energy of radicals created during sonolysis of the solvent (hydroxyl and hydrogen peroxide for water), which results in a high extractive power of ultrasounds [START_REF] Chemat | Applications of ultrasound in food technology: processing, preservation and extraction[END_REF][START_REF] Rawson | Effect of thermal and non thermal processing technologies on the bioactive content of exotic fruits and their products: Review of recent advances[END_REF]. Ultrasoundassisted extraction (UAE) is mainly based on acoustic cavitation and its hydrodynamic shear forces (principle presented in Figure I.11). US treatment has some advantages and benefits to extract valuable bio-compounds from samples. In particular, US offers greater penetration of the solvent into cellular material, shorter processing and residence time, higher product yields and reproducibility, lower solvent and emulsifiers consumption, higher processing throughput, significant savings in maintenance, less energy needed for processing, and finally, due to the mentioned facts, greener and cumulative cheaper processing (Barba et al., 2015b;[START_REF] Deng | The effects of conventional and non-conventional processing on glucosinolates and its derived forms, isothiocyanates: extraction, degradation, and applications[END_REF]Roselló-Soto et al., 2015b).

Ultrasound power and frequency

Ultrasound input power is the actual heat dissipated in the solvent, which is commonly calculated by calorimetry as Eq. (I.2) [START_REF] Contamine | Power measurement in sonochemistry[END_REF][START_REF] Toma | A calorimetric study of energy conversion efficiency of a sonochemical reactor at 500 kHz for organic solvents[END_REF].

(I.2)
where C p is the heat capacity of the solvent at constant pressure (J/(g•°C)), m is the mass of solvent (g), and dT/dt is the temperature gradient.

In general, the increase of ultrasound power can reduce extraction time and enhance extraction yield (Chemat et al., 2017b;[START_REF] Wei | Composition and bioactivity of tea flower polysaccharides obtained by different methods[END_REF]. [START_REF] Yue | Ultrasound-assisted extraction, HPLC analysis, and antioxidant activity of polyphenols from unripe apple[END_REF] showed that the TPC extraction yield from apple increased with the increase of ultrasound power. US frequency can also impact the extraction process due to effect on the bubble resonance size (Chemat et al., 2017b). The most commonly applied frequencies for UAE processes are in the diapason from 20 kHz to100 kHz.

Ultrasound intensity

Ultrasound intensity presents the transmitted energy every second and every square meter of emitting surface. It is directly related to the amplitude of the transducer and calculated as the following Eq. I.3 [START_REF] Tiwari | Ultrasound: A clean, green extraction technology[END_REF].

(I.3)
Where UI is the ultrasound intensity (W/cm 2 ), P is the ultrasound power (W), as calculated by the Eq. I.2, and S is the emitting surface of the transducer (cm 2 ).

Previous studies showed that 20.9 W/cm 2 was the optimal ultrasound intensity for soybean oil extraction due to the yield decreasing at higher UI [START_REF] Li | High intensity ultrasound-assisted extraction of oil from soybeans[END_REF]. A similar tendency was observed by W. Wang et al. (2015) for ultrasound pectin extraction at 20 kHz indicating that UI (from 10.18-14.26 W/cm 2 ) should be subjected to optimization, since the highest value of UI did not lead to the highest yields. Therefore, the optimal UI needs to be found for different products, extraction conditions and extracted components.

Characteristics of ultrasonic probe

The shape and diameter of ultrasonic probe have influences on the extraction behavior.

Generally, the stepped probe shape can give the highest amplitude magnification and the exponential probe shape can offer the smallest diameters (Chemat et al., 2017b). In addition, the material of ultrasonic probe has influence on the extraction effectiveness due to the erosion of probe, which can release metal particles into extraction medium [START_REF] Cravotto | Improved extraction of vegetable oils under high-intensity ultrasound and/or microwaves[END_REF]. At present, the most material used for ultrasound probe emitters is titanium alloy, since this material is thermo-resistant and behaves well under corrosive conditions (Chemat et al., 2017b).

Solvent

The molecular affinity between the solvent and the solute, and the solubility of the extracted components are the most important factors for the selection of a solvent. Cavitation phenomena produced by US are related to the physical properties of the solvent, including viscosity, surface tension and vapor pressure [START_REF] Mason | General principles[END_REF]. They found that the intensity of cavitation decreased with the increase of viscosity, vapor pressure and surface tension. [START_REF] Li | High intensity ultrasound-assisted extraction of oil from soybeans[END_REF] proved that the higher oil yield was obtained using UAE with isopropanol than with hexane as a solvent. This was due to the fact that vapor pressure of hexane is in five times higher than that of isopropanol. The collapse of cavitation bubble is more intense in solvents with lower vapor pressure [START_REF] Flannigan | Inertially confined plasma in an imploding bubble[END_REF].

Characteristics of samples

Effectiveness of UAE for different samples depends on the particle size, structure, texture and composition of the sample [START_REF] Vilkhu | Ultrasonic recovery and modification of food ingredients[END_REF]. The characteristics of samples can affect their sensitivity to the ultrasonic pressure waves [START_REF] Vinatoru | An overview of the ultrasonically assisted extraction of bioactive principles from herbs[END_REF]. Cavitation bubbles can more easily interact with samples having porous surface [START_REF] Li | High intensity ultrasound-assisted extraction of oil from soybeans[END_REF]. In addition, the turgidity of samples and the mobility of certain particles (such as starch and protein) in the cell cytoplasm both could influence the energy dissipation of ultrasound [START_REF] Zhang | Sonication enhanced cornstarch separation[END_REF].

Temperature

The temperature is another factor to affect solvent's characteristics, such as viscosity, surface tension and vapor pressure. High temperature can reduce the sonochemical effects due to the decrease of collapse of cavitation bubbles (Sališová et al., 1997). Previous study showed that the increase of temperature could lead to higher extraction yield [START_REF] Barroso | Adsorption of olive leaf (Olea europaea L.) antioxidants on silk fibroin[END_REF]. The effect of temperature (from 20 °C to 70 °C) for UAE was studied and compared with non-sonicated extractions [START_REF] Shahidi | Phenolics and polyphenolics in foods, beverages and spices: Antioxidant activity and health effects--A review[END_REF]. The study presented that the extraction yields increased with the increase of extract temperature.

However, the effectiveness is decreased when the temperature is close to the solvent's boiling point. Some studies demonstrated that relatively low temperature was beneficial for UAE [START_REF] Esclapez | Ultrasound-assisted extraction of natural products[END_REF][START_REF] Palma | Ultrasound-assisted extraction and determination of tartaric and malic acids from grapes and winemaking by-products[END_REF]. The efficiency of aqueous UAE of polyphenols from dried apple pomace at mild temperatures (40 °C) was confirmed [START_REF] Pingret | Lab and pilot-scale ultrasound-assisted water extraction of polyphenols from apple pomace[END_REF]. Optimal temperature (30 o C) was permitted to obtain the highest yield of extracted oil from flaxseed (Z.-S. Zhang et al., 2008). However extraction temperature varies according to the type of samples and the target compound of extraction (H.-F. Zhang et al., 2009;[START_REF] Zhang | Response surface optimization of ultrasound-assisted oil extraction from autoclaved almond powder[END_REF].

I.3.2.4.5 Ultrasound assisted extraction from apples

Nowadays, some studies have proved the potential of ultrasounds as an energetic assistance in polyphenols extraction from apples in terms of yields and duration of the process [START_REF] Virot | Towards the industrial production of antioxidants from food processing by-products with ultrasoundassisted extraction[END_REF]. UAE was beneficial to increase the antioxidant activity of apple pomace extracts [START_REF] Pingret | Lab and pilot-scale ultrasound-assisted water extraction of polyphenols from apple pomace[END_REF]. TPC obtained by UAE were on 30% higher than those obtained by conventional extraction. US-assisted extraction of polyphenols from apple is a time-saving, value-added, and environment-friendly process for the preparation of natural strong antioxidants [START_REF] Yue | Ultrasound-assisted extraction, HPLC analysis, and antioxidant activity of polyphenols from unripe apple[END_REF] increased the TPC more than 20% as compared with conventional extraction [START_REF] Virot | Towards the industrial production of antioxidants from food processing by-products with ultrasoundassisted extraction[END_REF]. Similar results were obtained for UAE using ethanol 56% at 80 °C for 30 min or acetone 65% at 25 °C for 60 min, respectively [START_REF] Wijngaard | The optimisation of solid--liquid extraction of antioxidants from apple pomace by response surface methodology[END_REF]. In addition, application of aqueous UAE allowed increasing the TPC from dried apple pomace by 30% as compared with conventional extraction at mild temperature (40 °C) [START_REF] Pingret | Lab and pilot-scale ultrasound-assisted water extraction of polyphenols from apple pomace[END_REF].

Note that different processing factors can affect the efficiency of UAE of polyphenols and their purity (Chemat et al., 2017b;[START_REF] Pingret | Lab and pilot-scale ultrasound-assisted water extraction of polyphenols from apple pomace[END_REF].

Previous studies showed that the US-assisted extraction was widely recognized as green technique with reduced energy consumption and processing time, low quantity of wastes and easily used on industrial scale (Chemat et al., 2017a(Chemat et al., , 2017b)). Particularly, US treatment is beneficial on selectivity of polyphenols extraction from apple products [START_REF] Pingret | Lab and pilot-scale ultrasound-assisted water extraction of polyphenols from apple pomace[END_REF][START_REF] Virot | Towards the industrial production of antioxidants from food processing by-products with ultrasoundassisted extraction[END_REF][START_REF] Wang | Selectivity of ultrasound-assisted aqueous extraction of valuable compounds from flesh and peel of apple tissues[END_REF][START_REF] Yue | Ultrasound-assisted extraction, HPLC analysis, and antioxidant activity of polyphenols from unripe apple[END_REF]. Therefore, the US treatment was selected as the intensified technology for extracting polyphenols in present thesis. In addition, purification of extracted polyphenols is required in order to obtain higher concentration of polyphenols.

I.4 Polyphenols purification Technology

I.4.1 Introduction

Commonly, purification of extracted polyphenols is required in order to get a higher concentration of polyphenols by removing the residual solid particles and undesirable molecules (such as proteins and sugars) [START_REF] Boussetta | Pulsed electrical technologies assisted polyphenols extraction from agricultural plants and bioresources: a review[END_REF]. Solvent extraction is a conventional technique for the recovery of polyphenols, but its selectivity for polyphenols recovery is poor. Efficient, selective and environmentally friendly purification technologies are still required. In recent years, many polyphenol purification technologies were studied, including adsorption and desorption on macroporous resin, precipitation, crystallization, and membrane filtration [START_REF] Conidi | Purification of artichoke polyphenols by using membrane filtration and polymeric resins[END_REF][START_REF] Nawaz | Extraction of polyphenols from grape seeds and concentration by ultrafiltration[END_REF][START_REF] Sun | Simultaneous separation and purification of total polyphenols, chlorogenic acid and phlorizin from thinned young apples[END_REF][START_REF] Tsujita | Purification and characterization of polyphenols from chestnut astringent skin[END_REF][START_REF] Watson | Polyphenols in plants: isolation, purification and extract preparation[END_REF][START_REF] Yang | Purification and characterization of polyphenol oxidase from banana (Musa sapientum L.) pulp[END_REF]. Pilot scale resin adsorption was used to recover and fractionate apple polyphenols (D. R. Kammerer et al., 2010). The efficiency of eight macroporous resins for simultaneous separation and purification of total polyphenols, chlorogenic acid, and phlorizin from thinned young apples were compared. Results demonstrated that X-5 resin presented the best adsorption and desorption efficiency for total polyphenols [START_REF] Sun | Simultaneous separation and purification of total polyphenols, chlorogenic acid and phlorizin from thinned young apples[END_REF]. The purification process by ultrafiltration (UF) after extraction of polyphenols from grape seeds could provide high extraction rates and extraction selectivity.

The obtained results showed that the maximum amount of polyphenols (11.4% of the weight of total seeds) from grape seeds could be recovered by UF process [START_REF] Nawaz | Extraction of polyphenols from grape seeds and concentration by ultrafiltration[END_REF]. The combination of an adsorption/desorption system (adsorbents resins) with a membrane filtration system (UF and nanofiltration, NF) produces more purified fraction of phenolic compounds from artichoke wastewaters compared to an individual process fully based on the filtration with the use of adsorbents resins or membrane [START_REF] Conidi | Purification of artichoke polyphenols by using membrane filtration and polymeric resins[END_REF]. In addition, the previous study presented that dialysis technology, using Diaion HP-20 and Sephadex LH-20 columns, was beneficial for the purification of extracted polyphenols from chestnut astringent peels [START_REF] Tsujita | Purification and characterization of polyphenols from chestnut astringent skin[END_REF]. Among these purification technologies, the adsorption and desorption with resins and the membrane filtration are most widely used for the purification of polyphenols extracts.

I.4.2 Adsorption and desorption

I.4.2.1 Introduction

Nowadays, many types of absorbents have been applied for adsorption and desorption processes, such as activated carbons, mineral adsorbents (siliceous materials, clay, natural zeolites), and resins (ion-exchange resins and macroporous resins). Especially, concentration and purification of polyphenols have been widely studied using macroporous resins (J. Kammerer et al., 2010;[START_REF] Silva | Optimisation of the adsorption of polyphenols from Inga edulis leaves on macroporous resins using an experimental design methodology[END_REF][START_REF] Soto | Recovery, concentration and purification of phenolic compounds by adsorption: a review[END_REF]. Polyphenols are firstly adsorbed on the resin surface due to the strong noncovalent bonding and aromatic stacking.

Following desorption of polyphenols from resins occurs into organic solvents. The previous studies demonstrated the effectiveness of macroporous resin adsorption/desorption for purification and concentration of bio-compounds obtained from the extracts of fruits and vegetables (T. Liu et al., 2010;[START_REF] Seeram | Rapid large scale purification of ellagitannins from pomegranate husk, a by-product of the commercial juice industry[END_REF]T. Wang et al., 2015;[START_REF] Barkakati | Adsorptive separation of Ginsenoside from aqueous solution by polymeric resins: Equilibrium, kinetic and thermodynamic studies[END_REF][START_REF] Saleh | Comparison of conventional and ultrasonically assisted extractions of pharmaceutically active compounds from Salvia officinalis[END_REF][START_REF] Li | Characterization and evaluation of a macroporous adsorbent for possible use in the expanded bed adsorption of flavonoids from Ginkgo biloba L[END_REF][START_REF] Silva | Optimisation of the adsorption of polyphenols from Inga edulis leaves on macroporous resins using an experimental design methodology[END_REF].

I.4.2.2 Operational parameters influencing adsorption and desorption

Adsorbent characteristics affect importantly adsorption [START_REF] Brune | Correlation between adsorption and small molecule hydrogen bonding[END_REF][START_REF] Cheng | Effects of multiple weak interactions on the binding of phenolic compounds by polymeric adsorbents[END_REF][START_REF] Dargaville | The adsorption of multinuclear phenolic compounds on activated carbon[END_REF][START_REF] Geng | High selective purification of flavonoids from natural plants based on polymeric adsorbent with hydrogen-bonding interaction[END_REF][START_REF] Navarro | Comparative study of the removal of phenolic compounds by biological and non-biological adsorbents[END_REF][START_REF] Pan | Application of an effective method in predicting breakthrough curves of fixed-bed adsorption onto resin adsorbent[END_REF]. There are various absorbents used for polyphenols purification, such as activated carbon, reverse phase silica gels and resins. For instance, activated carbon is used to recover polyphenols from grape juice [START_REF] Soto | Charcoal adsorption of phenolic compounds present in distilled grape pomace[END_REF]; reverse phase silica gels are beneficial for anthocyanin recover from aronia melanocarpa [START_REF] Kraemer-Schafhalter | Solid-phase extraction (SPE)-a comparison of 16 materials for the purification of anthocyanins from aronia melanocarpa var Nero[END_REF]. Among these absorbents, macroporous resins (Table I.6) have been widely used in the separation and purification of plant polyphenols due to their physicochemical stability, high adsorption selectivity and easy recycling. This concerns especially AB-8 macroporous resin [START_REF] Wan | Enrichment and purification of total flavonoids from Flos Populi extracts with macroporous resins and evaluation of antioxidant activities in vitro[END_REF]. Macroporous resins are durable polar, non-polar or slightly hydrophilic polymers with high adsorption capacities for organic molecules through appropriate surface area and nuclear pore size, electrostatic force, hydrogen bonding interactions, hydrophobic interactions and complexation [START_REF] Fu | Optimization of luteolin separation from pigeonpea [Cajanus cajan (L.) Millsp.] leaves by macroporous resins[END_REF][START_REF] Gao | Separation of scutellarin from crude extracts of Erigeron breviscapus (vant.) Hand. Mazz. by macroporous resins[END_REF]. Polyphenol molecules can form hydrogen bonds by interactions between surface functional groups (hydroxyl and carboxyl groups) of polyphenols and macroporous resins. Therefore macroporous resins are beneficial for polyphenols separation and purification (J. Kammerer et al., 2010). In addition, internal porous structure of absorbents and properties of target compounds of solution also have influence on the adsorption and desorption processes [START_REF] Garcia-Araya | Activated carbon adsorption of some phenolic compounds present in agroindustrial wastewater[END_REF]. SDVB: styrene-divinylbenzene.

Apart from adsorbent characteristic, the values of pH, ionic strength, polarity and the temperature of extracts will also affect the effectiveness of adsorption and desorption processes (Bayç n et al., 2007;[START_REF] Ramos | Recovery of Vitamin B12 and cephalosporin-C from aqueous solutions by adsorption on non-ionic polymeric adsorbents[END_REF][START_REF] Silva | Optimisation of the adsorption of polyphenols from Inga edulis leaves on macroporous resins using an experimental design methodology[END_REF]. The interactions of solutes and adsorbents presented different mechanisms at different pH [START_REF] Caetano | Phenol removal from aqueous solution by adsorption and ion exchange mechanisms onto polymeric resins[END_REF][START_REF] Carmona | Combined adsorption and ion exchange equilibrium of phenol on Amberlite IRA-420[END_REF]. At acidic pH range, the adsorption of phenolics will be enhanced because the phenols are undissociated and the dispersion interactions predominate [START_REF] Caqueret | Purification of sugar beet vinasse-adsorption of polyphenolic and dark colored compounds on different commercial activated carbons[END_REF][START_REF] Dąbrowski | Adsorption of phenolic compounds by activated carbon-a critical review[END_REF][START_REF] Mohanty | Adsorption of phenol from aqueous solutions using activated carbons prepared from Tectona grandis sawdust by ZnCl2 activation[END_REF][START_REF] Scordino | Adsorption of flavonoids on resins: cyanidin 3-glucoside[END_REF][START_REF] Silva | Optimisation of the adsorption of polyphenols from Inga edulis leaves on macroporous resins using an experimental design methodology[END_REF][START_REF] Ugurlu | Removal of phenolic and lignin compounds from bleached kraft mill effluent by fly ash and sepiolite[END_REF]. While the adsorption will be decreased at alkaline pH due to the dissociation of hydroxyl and carboxyl groups [START_REF] Fu | Optimization of luteolin separation from pigeonpea [Cajanus cajan (L.) Millsp.] leaves by macroporous resins[END_REF]. Both positive and negative effects of temperature have been reported for polyphenols purification by macroporous resins [START_REF] Gökmen | Effect of pretreatment with gelatin and bentonite on permeate flux and fouling layer resistance during apple juice ultrafiltration[END_REF][START_REF] Ugurlu | Removal of phenolic and lignin compounds from bleached kraft mill effluent by fly ash and sepiolite[END_REF]. High temperature can increase the rate of mass transfer through cell membrane and into the pores of absorbent due to the decrease of solution viscosity. However, high temperatures may promote irreversible interactions [START_REF] Qiu | Study upon kinetic process of apple juice adsorption decoloration by using adsorbent resin[END_REF]. Optimal adsorption temperature depends on the purification component, applied absorbent and properties of extracts [START_REF] Garcia-Araya | Activated carbon adsorption of some phenolic compounds present in agroindustrial wastewater[END_REF][START_REF] Ku | Removal of phenols from aqueous solution by XAD-4 resin[END_REF]. In addition, the presence of molecular oxygen in aqueous solutions can also influence the adsorption of polyphenolics onto resins [START_REF] Saleh | Comparison of conventional and ultrasonically assisted extractions of pharmaceutically active compounds from Salvia officinalis[END_REF]. The adsorption of aromatic compounds will be increased with the increase of molecular oxygen in aqueous solutions by dispersive/repulsive, donor/acceptor and hydrogen-bonding interactions [START_REF] Dąbrowski | Adsorption of phenolic compounds by activated carbon-a critical review[END_REF][START_REF] Franz | Effect of chemical surface heterogeneity on the adsorption mechanism of dissolved aromatics on activated carbon[END_REF].

I.4.2.3 Application of adsorption and desorption for polyphenols purification

In previous studies, adsorption and desorption technique has been applied for separation and purification of anthocyanins from mulberry [START_REF] Chen | Adsorption properties of macroporous adsorbent resins for separation of anthocyanins from mulberry[END_REF] and blueberry [START_REF] Buran | Adsorption/desorption characteristics and separation of anthocyanins and polyphenols from blueberries using macroporous adsorbent resins[END_REF], total polyphenols, chlorogenic acid and phlorizin from thinned young apples [START_REF] Sun | Simultaneous separation and purification of total polyphenols, chlorogenic acid and phlorizin from thinned young apples[END_REF], individual phenolic compounds from apple juice [START_REF] Kammerer | Adsorptive recovery of phenolic compounds from apple juice[END_REF] and phenolic compounds from grape marc [START_REF] Zagklis | Purification of grape marc phenolic compounds through solvent extraction, membrane filtration and resin adsorption/desorption[END_REF]. For extracts of unripe apples, X-5 macroporous resin was confirmed to present the best adsorption capacity and desorption ratio for total polyphenols compared with different macroporous resins. After adsorption and desorption with X-5 resin, the polyphenols content was increased in 2.12-fold (from 35.17% to 74.64%) with a recovery yield of 89.35%. In addition, chlorogenic acid and phlorizin were selectively purified using X-5 resins, with the purities of 15.20% and 97.52%, and recovery yields of 89.16% and 64.95%, respectively [START_REF] Sun | Simultaneous separation and purification of total polyphenols, chlorogenic acid and phlorizin from thinned young apples[END_REF]. Quantification and selective purification of phenolic compounds presented in apple juice [START_REF] Kammerer | Adsorptive recovery of phenolic compounds from apple juice[END_REF] and apple pomace [START_REF] Carle | Method for obtaining useful materials from the by-products of fruit and vegetable processing[END_REF][START_REF] Kammerer | Recovery and fractionation of major apple and grape polyphenols from model solutions and crude plant extracts using ion exchange and adsorbent resins[END_REF][START_REF] Saleh | Comparison of conventional and ultrasonically assisted extractions of pharmaceutically active compounds from Salvia officinalis[END_REF][START_REF] Schieber | A new process for the combined recovery of pectin and phenolic compounds from apple pomace[END_REF] were done.

Numerous studies confirmed that adsorption/desorption process was effective for the purification of valuable natural products from food and plant sources. However, the purity of the products may vary from 10 to 90% depending on the complexity of the composition of the crude extracts [START_REF] Li | Development of adsorptive (non-ionic) macroporous resins and their uses in the purification of pharmacologically-active natural products from plant sources[END_REF]. Therefore, more effective separation methods are required in order to improve the separation and purification efficiency. ). The permeate is the part of the feed passing through the membrane, while the retentate is another part of the feed, which does not pass through the membrane. The goal component can be retained by the membrane in the retentate or pass through the membrane in the permeate. Nowadays, pressure driven membrane operations have been widely employed for various food products, such as dairy products, fruit juices, wine, vegetable oils, potable water, and agricultural wastewaters. The driving force of these processes is represented by a pressure gradient applied between the two sides of membrane. According to the transmembrane pressure (TMP) and the membrane pore size, membrane filtration is usually divided into four pressure-driven processes: microfiltration (MF, 0.1-5 μm, 1-10 bar), ultrafiltration (UF, 0.5-100 nm, 1-10 bar), nanofiltration (NF, 0.5-10 nm, 10-30 bar)

and reverse osmosis (RO, <0.5 nm, 35-100 bar) [START_REF] Cui | Fundamentals of pressure-driven membrane separation processes[END_REF]. The application of different membrane separation and purification processes based on particle or molecular sizes is presented in Fig. I.14. RO process is widely used for desalination and water purification, while the UF and MF processes are widely used in food and bioprocessing. Especially, UF is most widely used for the purification of polyphenols by separating of undesirable components from liquids. UF membranes can retain molecules within the molecular weight (MW) more than 1000 MW (i.e. protein molecules) from passing through the membranes, thus low molecular weight components can be purified [START_REF] García | Bioseparation process science[END_REF]. Since the MW of various polyphenols are less than 1000 (Table I.7), polyphenol molecules are allowed to pass through UF membrane and thus to be purified from high molecular weight components [START_REF] Nawaz | Extraction of polyphenols from grape seeds and concentration by ultrafiltration[END_REF].

I.4.3.2 Materials of filtration membranes

A membrane is a thin layer of semi-permeable material that permits the separation of certain species containing in a fluid. Membranes for filtration are usually divided into two types from materials (polymeric membranes and inorganic membranes). Especially, polymeric membranes have had more applications for practical use in the areas of food, beverage, and biotechnology [START_REF] Bhave | Inorganic Membranes Synthesis, Characteristics and Applications: Synthesis, characteristics, and applications[END_REF]. Among polymeric membranes, materials for MF and UF are mainly Polyacrylonitrile (PAN), Cellulose acetate (CA), Polysulphone (PS), Polyethersulphone (PES) and Poly (vinylidene difluoride) (PVDF) [START_REF] Cassano | Effect of polyphenols-membrane interactions on the performance of membrane-based processes[END_REF].

Each of these materials has different properties with respect to the surface charge, degree of (1) Dead-end filtration

The principle of the dead-end filtration is to filter the feed perpendicularly to the surface of the membranes (Fig. I.16a). All particles in feed with the size larger than the pore sizes of the membrane are stopped at its surface to form the cake layer. The thickness of the cake layer is determined by the TMP and the flow rate, which are related to the specific resistance of the cake.

(2) Cross-flow filtration For cross-flow filtration, the feed flows tangentially to the surface of the membrane, thus establishing a trans-membrane pressure which limits the accumulation of cake (Fig.

I.16b).

Cross-flow filtration allows small particles to pass through the membrane and remains larger particles to flow along the membrane by cleaning the membrane surface. Finally, the equilibrium can be reached and the flow can stabilize in a stationary state. The cross-flow filtration can prevent larger particles from building up a cake layer on the membrane surface.

(3) Dynamic filtration with rotating disk

For the dynamic filtration with rotating disk, the feed flows perpendicularly to the surface of the membranes as in dead-end filtration. However, dynamic filtration with rotating disk can produce a relative movement between the membrane and the cell, which generates a higher shear. The filter cell is equipped with a stirrer near the membrane surface, generating high shear rates on the surface of membrane to decrease membrane fouling. The intensity of shear mainly depends on the feed. The feed between stirrer and membrane is tangential to the membrane, therefore a part of the particles are kept in suspension and do not remain on the Cross-flow filtration [START_REF] Ketola | Determination of surfactants in industrial waters of paper-and board mills[END_REF], c) Dynamic filtration with rotating disk [START_REF] Bouzerar | Influence of geometry and angular velocity on performance of a rotating disk filter[END_REF] .

I.4.3.4 Application of membrane filtration

Membrane filtration performs purification, recovery, concentration and fractionation of solutes from by-products and biomass wastes [START_REF] Castro-Muñoz | Phenolic compounds recovered from agro-food by-products using membrane technologies: an overview[END_REF]. Nowadays, membrane technologies (especially UF with PES and PVDF membranes) have been widely used for the subsequent step of polyphenol purification and concentration from different raw materials [START_REF] Borneman | Selective removal of polyphenols and brown colour in apple juices using PES/PVP membranes in a single ultrafiltration process[END_REF][START_REF] Liu | Comparative study of ultrasoundassisted and conventional stirred dead-end microfiltration of grape pomace extracts[END_REF][START_REF] Youn | Effective clarifying process of reconstituted apple juice using membrane filtration with filter-aid pretreatment[END_REF][START_REF] Zhu | Study of rotating disk assisted dead-end filtration of chicory juice and its performance optimization[END_REF]. For instance, UF had been used to purify polyphenols of flaxseed hull extracts by separating proteins [START_REF] Loginov | Separation of polyphenols and proteins from flaxseed hull extracts by coagulation and ultrafiltration[END_REF]. A cross-flow UF pilot was effective to separate and purify polyphenols from pomegranate juice [START_REF] Conidi | Separation and purification of phenolic compounds from pomegranate juice by ultrafiltration and nanofiltration membranes[END_REF]. In addition, the effect of PES membranes with a molecular weight cut-off (MWCO) of 50 kDa during UF process for the purification of polyphenols in retentates from vine-shoot extracts was compared and analyzed [START_REF] Rajha | Effect of alternative physical pretreatments (pulsed electric field, high voltage electrical discharges and ultrasound) on the dead-end ultrafiltration of vine-shoot extracts[END_REF]. For apple products, many previous studies analyzed the effect of membrane pore size on the permeate flux and the purification of polyphenols from apple juice [START_REF] Vladisavljević | Permeate flux and fouling resistance in ultrafiltration of depectinized apple juice using ceramic membranes[END_REF][START_REF] Zárate-Rodríguez | Effect of membrane pore size on quality of ultrafiltered apple juice[END_REF] and apple cider [START_REF] Zhao | The effect of apple cider characteristics and membrane pore size on membrane fouling[END_REF].

Different kinds of membranes were compared to purify polyphenols from apple juice in the dead-end mode [START_REF] Borneman | Selective removal of polyphenols and brown colour in apple juices using PES/PVP membranes in a single ultrafiltration process[END_REF] and from apple cider in the cross-flow mode [START_REF] Zhao | The effect of apple cider characteristics and membrane pore size on membrane fouling[END_REF].

I.4.3.5 Membrane electro-filtration

Nowadays, the biggest problem during membrane filtration is membrane fouling. The fouling reduces permeate flux and decreases the polyphenols purification efficiency by modifying membrane permeability and molecular selectivity [START_REF] Merkel | Ultrapermeable, reverse-selective nanocomposite membranes[END_REF]. Membrane fouling is due to pore constriction, pore blocking and cake layer formation (polyphenols may interact together and with other compounds to form large particles) on the membrane surface [START_REF] Guo | A mini-review on membrane fouling[END_REF]. In order to reduce the membrane fouling during polyphenols purification process, many technologies have been studied [START_REF] Cai | Effects of ultrasound on ultrafiltration of Radix astragalus extract and cleaning of fouled membrane[END_REF][START_REF] Duclos-Orsello | A three mechanism model to describe fouling of microfiltration membranes[END_REF][START_REF] Jaffrin | Dynamic shear-enhanced membrane filtration: a review of rotating disks, rotating membranes and vibrating systems[END_REF][START_REF] Rai | Resistance in series model for ultrafiltration of mosambi (Citrus sinensis (L.) Osbeck) juice in a stirred continuous mode[END_REF][START_REF] Wakeman | Additional techniques to improve microfiltration[END_REF], especially the ''force fieldassisted methods''(including electrical, magnetic and sonic forces) [START_REF] Chen | Study of the influence of the electric field on membrane flux of a new type of membrane bioreactor[END_REF][START_REF] Wakeman | Additional techniques to improve microfiltration[END_REF].

Membrane electro-filtration is a process in which charged solutes (such as proteins, organic colloids, and bacteria) are taken away from the surface of the membrane by employing direct current (DC) electrical field [START_REF] Li | Membrane fouling mitigation by coupling applied electric field in membrane system: Configuration, mechanism and performance[END_REF]. Membrane electro-filtration can reduce concentration polarization and membrane fouling [START_REF] Lee | Electro-ultrafiltration study on Aldrich humic substances with different molecular weights[END_REF], consequently the particles mass transfer and permeate flux may be enhanced [START_REF] Song | Rapid concentration of protein solution by a crossflow electro-ultrafiltration process[END_REF][START_REF] Tarleton | The role of field-assisted techniques in solid/liquid separation[END_REF]. The effects of membrane electro-filtration for various solutions have been studied [START_REF] Liu | A study on critical electric field strength of electromembrane filtration for low concentration suspension[END_REF][START_REF] Zhao | Research on membrane surface micro-particle deposition control by electrophoresis[END_REF]. For instance, membrane electro-filtration could improve liquid-solid separation, permeate flux, quality of filtrate, as well as fouling removal of drinking water and waste water [START_REF] Mostafazadeh | Electrofiltration technique for water and wastewater treatment and bio-products management: A review[END_REF]. Dead-end membrane electro-filtration could improve biopolymer recovery and permeate flux [START_REF] Hofmann | Improvement of dead-end filtration of biopolymers with pressure electrofiltration[END_REF]. Cross-flow membrane electro-ultrafiltration was beneficial to enhance permeate flux of synthetic juice (mixture of sucrose and pectin) [START_REF] Sarkar | A study of electric field enhanced ultrafiltration of synthetic fruit juice and optical quantification of gel deposition[END_REF] and rapidly purify dilute protein solutions [START_REF] Song | Rapid concentration of protein solution by a crossflow electro-ultrafiltration process[END_REF]. Therefore membrane electro-filtration was regarded as an effective filtration method to decrease membrane fouling and improve purification efficiency of valuable components from product extracts.

I.5 Conclusions and research objectives

Phenolic composition of apple peels is very rich and consists mainly of flavanols and dihydrochalcones. Content of phenolics in apple peels is higher than in the juice or flesh of In the third step, purification process was implemented for obtaining higher concentration of polyphenols extracts. The adsorption/desorption and membrane filtration have emerged.

These techniques have the advantage of being selective, high productivity, short duration and low energy and operation consumption. Adsorption/desorption with macroporous resins and membrane techniques have shown their interests but sometimes they are confronted with some obstacles. Ultrasound-assisted adsorption/desorption and membrane electro-filtration were studied to increase purification efficiency and reduce filtration time.

In this context, the issues addressed by this work are for the extraction and purification of polyphenols from apple peels. The main objectives of this thesis are:

(1) Study the effects of ultrasound treatment on extraction selectivity of valuable compounds from apple products.

(2) Study the mechanisms of cavitation phenomenon induced by ultrasound.

(3) Analysis of correlations between disintegration degree of peel cells induced by US and efficiency of bio-compounds extraction from fruit peels.

(4) Compare and increase the performance of the two purification technologies (adsorption/desorption filtration and membrane filtration) of apple peel extracts.

Chapter II Materials and Methods

II.1 Raw materials

Peels, flesh and pomace of apples and some other fruit peels (bananas, persimmons and plums) were used as raw materials (Fig. II.1). The introduction of each of these products will be detailed in the following.

II.1.1 Apple peels

Commercial green apples (Granny Smith) and red apples (Red delicious, Gala) were selected as the raw material for investigation (Fig. II.1a). The apples with good and uniform quality and near-spherical shape were purchased at the local supermarket (Compiegne, France). The initial moisture content of apple peel on wet basis (83.07 g/100 g for green apples, 85.39 g/100 g for red apple (Red delicious) and 84.34 g/100 g for red apple (Gala))

was determined using MA 160 infrared moisture analyzer (Sartorius, Göttingen, Germany).

II.1.2 Apple flesh

Commercial green apples (Granny Smith) and red apples (Red delicious) were purchased at the local supermarket (Compiegne, France) (Fig. II.1b). The apples were with good and uniform quality and near-spherical shape. The initial moisture content of apple flesh on wet basis (83.74 g/100 g for green apples, and 87.44 g/100 g for red apple) was determined using MA 160 infrared moisture analyzer (Sartorius, Göttingen, Germany). The samples of good and uniform quality (with nearly spherical shape for persimmons and plums, and near the same size for bananas) were stored at 4 °C. Perrier water was stored at room temperature until needed. All experimental data were collected within 10 days of the purchase of the samples. The initial moisture content of peels on wet basis (89% for bananas, and 76% for persimmons) was determined using MA 160 infrared moisture analyzer (Sartorius, Göttingen, Germany).

II.1.3 Apple pomace

II.1.5 Adsorbents

The hydrophobic poly-aromatic adsorbent Amberlite XAD-16 (Sigma Aldrich, France) was used in adsorption experiments. The resin XAD-16 has a surface area of 900 m 2 /g, mean pore radius of 5.0 nm, pore volume of 1.82 mL/g and dry density of 1.08 g/mL.

II.1.6 Filtration membranes

The main properties of used membranes are presented in Table II.1. Four types of hydrophilic polyethersulphone (PES) filtration membranes were all purchased from Microdyn-Nadir (GmbH, Germany).

II.2 Extraction and purification experiments

II.2.1 Sample preparation

The flesh tissue (the disks with diameter of 20mm and thickness of 10 mm) was taken from the central part of the apple.

The peel tissue (thin slices with length of 20 mm, width of 10 mm) was removed from apples and persimmons with a razor blade (thickness of ≈0.1 mm) and from bananas by hand.

For preparation of the freeze-thawed products, the peel tissues (20 mm x 10 mm) were frozen at -20 °C for 12 h and then thawed at room temperature (≈23 °C) for 12 h.

The apple peel powders were prepared with peel tissues (20 mm x 10 mm). The fresh apple peel tissues were dried in a convection oven (UL50 [START_REF] Singleton | [END_REF]. Many previous researches showed that the polyphenol yield was increased with increasing temperature, but also that beyond a certain value (80 o C) most phenolic compounds would be denatured [START_REF] Gironi | Temperature and solvent effects on polyphenol extraction process from chestnut tree wood[END_REF][START_REF] Pinelo | Selective release of phenols from apple skin: Mass transfer kinetics during solvent and enzyme-assisted extraction[END_REF][START_REF] Spigno | Effects of extraction time, temperature and solvent on concentration and antioxidant activity of grape marc phenolics[END_REF]. Therefore, T in range of The adsorbent Amberlite XAD-16 (10g) was firstly soaked in 95% ethanol (100 mL) for 6h and rinsed with distilled water (until eluate was clear) in order to remove the impurities, porogenic agents and monomers trapped in the pores the resin. Then the absorbent was soaked in 5% hydrochloric acid, HCl (100 mL) for 6h, rinsed with distilled water (until neutral effluent), soaked in 5% sodium hydroxide, NaOH (100 mL) for 6h, and rinsed with distilled water (until neutral effluent). Finally, it was dried in a convection oven UL50 (Memmert, In the adsorption step the probes of liquid extract were periodically taken, centrifuged using Galaxy Mini Centrifuge C1413-230EU (VWR, Paris, France) for 1 min at 6000 rpm, and analyzed for the total polyphenol content, TPC.

Adsorption capacity (Q, mg/g dry resin) at equilibrium was calculated as:

Q=(C o -C e )V/M r II.2
where C o and C e are initial and equilibrium (final) concentrations of bio-molecules (e.g., polyphenols) (mg/mL) in extract solutions, M r is the mass of the resin (g) and V is the volume of the liquid medium (mL) in adsorption experiments.

In experiments with US-assisted adsorption, the preliminary pulsed sonication was applied at different US intensity, P (0-400W), in the same manner as described in II.2.2.2. The total number of pulses was n=20, US treatment time, t us =60 min, and the total time of US-assisted adsorption was t a =100 min. Then the adsorption in shaking bath was continued.

II.2.3.1.3 Desorption procedure

Desorption experiments were done using the absorbents previously saturated with biomolecules in the adsorption step. The adsorbent (2g) was put into the shaking glass beaker filled with aqueous ethanol solution (100 ml, C et =0-95%). Desorption experiments were performed at 25 o C for 180 min. In the course of desorption, the probes of liquid extract were periodically taken, centrifuged and analyzed for the soluble matter content, o Brix, and total polyphenol content, TPC.

The desorption ratio, D, was calculated as:

D=C tf V d /[(C o -C e )V a ] II.3
where C tf is the concentration of polyphenols (mg/mL) in the aqueous-ethanol solution, and V d is the volume of the liquid medium (mL) in desorption experiments.

The adsorption/desorption efficiency (recovery), R e , for phenolics, proteins and soluble matter content was calculated using the following equation: The rejection coefficient K rtf and sieving ratio R tf of total polyphenols are defined as:

K rtf =1-R tf =1-C tf /C tf0 II.5
where C tf and C tf0 are the concentration of total polyphenols in filtrate and initial feed (mg/mL), respectively.

The rejection coefficient K rpr and sieving ratio R pr of proteins are defined as:

K rpr =1-R pr =1-C pr /C pr0 II.6
where C pr and C pr0 are the concentration of proteins in filtrate and initial feed (mg/mL), respectively.

The rejection coefficient K rts and sieving ratio R ts of total solutes are defined as:

K rts =1-R ts =1-C ts /C ts0 II.7
where C ts and C ts0 are the concentration of total solutes in filtrate and initial feed, respectively.

The rejection coefficient K rI and sieving ratio R I of colour intensity are defined as:

K rI =1-R I =1-I/I 0 II.8
where I and I 0 are the colour intensity of filtrate and initial feed, respectively.

Volume ratio (V r ) is calculated as:

V r =V f /V 0 II.9
where V f and V 0 are the volume of final filtrate after filtration and initial feed (m 3 ), respectively.

The filtrate flux (J) is calculated as:

J=d V /Ad t II.10
where V is the filtrate volume at time t (m 3 ), A is the effective membrane area (m 2 ), and t is the filtration time (s).

The Ruth-Carman's equation which was applied for estimation of filter cake resistance in the dead-end filtration is calculated as [START_REF] Liu | Intensification of polyphenols extraction from grape seeds by high voltage electrical discharges and extract concentration by dead-end ultrafiltration[END_REF][START_REF] Loginov | Comparison of dead-end ultrafiltration behaviour and filtrate quality of sugar beet juices obtained by conventional and "cold" PEF-assisted diffusion[END_REF].

II.11

where t and V are the filtration time (s) and the filtrate volume (m 3 ), respectively, α is the specific filtration resistance of the filter-cake (m/kg), C cs is the weight fraction of cakeforming (colloidal and insoluble) solids in the feed (kg/kg), ρ is the density of filtrate (kg/m 3 ), μ is the viscosity of filtrate (Pa•s), A is the effective membrane area (m 2 ), ΔP is the filtration pressure (Pa), R m is the membrane resistance (m -1 ).

II.3 Physico-chemical analysis

II.3.1 Dry matter

The dry matter (DM) content in sample was determined after drying the apple flesh in MA II.3.2 Analysis of extracts

II.3.2.1 Soluble matter content

The concentration of total soluble matter, °Brix (g of DM/100 g solution), was measured using the refractometer (Atago, USA) at room temperature.

II.3.2.2 pH

The pH of solution was detected by a multifunction pH meter (PCE-PHD 1, PCE Instruments France EURL, France).

II.3.2.3 Electrical conductivity

The electrical conductivity, σ (ms/cm), of solution was detected by a multifunction pH meter (PCE-PHD 1, PCE Instruments France EURL, France).

II.3.2.4 Water holding capacity

A modified method was conducted to measure water holding capacity of apple peels [START_REF] Huang | The effect of extrusion processing on the physiochemical properties of extruded orange pomace[END_REF]. The surface moisture of apple peels after extraction experiment was wiped with filter paper. Then the apple peel samples were dried using MA 160 infrared moisture analyzer. Then ten milliliters of distilled water was added to 1 g of the dried apple peel samples. The suspension was homogenized in a vortex for 1 min and left at room temperature for 24 h. After centrifugation at 1000g for 5 min (Z200, Hermle Labortechnik GmbH, Wehingen), the supernatant was removed and the residue weighed. The water holding capacity was expressed as grams of water held by 1 g of fresh sample.

II.3.2.5 Particle size distribution

The particle size distributions in liquid extracts were analyzed using light scattering method with Malvern Mastersizer X (Malvern Instruments S.A., France). The measurements were done using the 45 mm lens and the optical pathway of 14.3 mm.

II.3.2.6 Hardness

The hardness tests for fruit peels were performed in a Texture Analyser (model TA-XT plus, Rhéo, Champlan, France). The samples were placed on the platform of the texture analyzer to carry out force deformation tests. The load force, F, was detected at deformation of 0.5 mm for all samples.

II.3.2.7 Thickness

The thickness of fruit peels, δ, was estimated using the scanning electron microscopy images (SEM) (Quanta FEG 250, Thermo Fisher Scientific, MA USA) at magnification of 50.

The high voltage and mode of SEM was 20 kV and SE, respectively. The length and width of the extraction region for all samples was 5 mm and 3.5 mm, respectively. The testing peel was fixed between two iron plates. For thinner samples, the edges of SEM images were visually brighter because of the iron light reflection.

II.3.2.8 Color

The colour of extracts (diluted 10 times) was measured by adsorbance at 420 nm (A 420 )

with UV/Vis instrument (Thermo Spectronic Genesys 20, Thermo Electron Corporation, MA, USA) [START_REF] Liu | Intensification of polyphenols extraction from grape seeds by high voltage electrical discharges and extract concentration by dead-end ultrafiltration[END_REF].

II.3.2.9 Turbidity

The turbidity of extracts was measured with a XR turbidimeter (HACH Company, Loveland, USA). For the turbidity measurement, the adsorption experiments with initial concentration of polyphenols C o =1 mg/mL were performed for 1500 min in presence of sonication during the first 100 min at different ultrasonic powers, P=0-400 W. Then solutions were clarified by sedimentation in the Earth's gravity for 15 min (g-samples) or by centrifugation for 1 min at 6000 rpm (c-samples).

II.3.2.10 Scanning electron microscopy

The scanning electron microscopy (SEM) images with magnification of 100 were registered using SEM instrument Quanta FEG 250 (FEI, Holland) applied in an accelerating voltage of 20 kV. The microscope was coupled to a CCD camera (Sony, Japan) connected to a computer.

II.3.2.11 Fourier transform infrared spectroscopy

Fourier transform infrared spectroscopy (FTIR) analysis of solutions was performed using Nicolet™ iS5 (iD3 ATR, Thermo Scientific, TM, USA) instrument. The FTIR transmittance (%) was recorded between 600 and 4000 cm -1 .

II.3.2.12 Optical images

The optical images of gas water solvents with different CO 2 concentration (0, 1.76, 3.53, 5.28, 7.05 mmol/L) before and after ultrasound treatment (W=0.242 kW•h/kg) were directly observed using a reflection optical microscope (Leitz Orthoplan, Germany) at magnification × 4. The microscope was coupled to a CCD camera (Sony, Japan) connected to a computer.

The gas water solvent was carefully got with a dropper, placed on a glass plate and observed with a cold lamp. The software 'Archimed' was used to register images and analyse the bubble size. In each experiment, 3 images from three different samples of one solution were analysed.

II.3.2.13 Total polyphenol content

The total polyphenols content (TPC) was determined using the Folin-Ciocalteu method based on a colorimetric oxidation/reduction reaction of phenols [START_REF] Singleton | [END_REF]. 0.2 mL of diluted extract and 1 mL of Folin-Ciocalteu reagent (Merck, Darmstadt, Germany)

(diluted 1:10 with water) were mixed. 0.8 mL of Na 2 CO 3 (75 g/L) (Prolabo, Fontenay-sous-Bois, France) was then added. The sample was incubated for 10 min at 50 °C and then cooled for 10 min at room temperature. For the control sample, 0.2 mL of distilled water was taken.

The absorbance was measured at 750 nm using UV/Vis instrument (Thermo Spectronic The relationship between absorbance Abs and the concentration of gallic acid, C G (μg/mL) was near linear, as following:

Abs=0.0204C G II.12

II.3.2.14 Catechin content

The concentration of catechin, C c , was estimated by fluorescence technique using the instrument Cary Eclipse Fluorescence Spectrofluorometer and 10mm fused-silica cuvette (Agilent Technologies, USA). The fluorescence spectra was obtained using the excitation at λ e =280 nm and registration of emission λ=312 nm [START_REF] Arts | Catechin contents of foods commonly consumed in The Netherlands. 1. Fruits, vegetables, staple foods, and processed foods[END_REF]. C s ≈kI f II.14

Here, k=1.39×10 -5 mg/mL and k=0.72×10 -5 mg/mL are slopes for C et =0 and C et = 10%, respectively.

For higher concentrations of ethanol (C et >10%) the extracts were diluted to the concentration C et =10 % and then analyzed. The used fluorescence technique allowed determination of C c in extracts using relatively small quantities of tested solutions.

II.3.2.15 Total flavonoid content

Total flavonoid content (TFC) was estimated according to the method previously described [START_REF] Liu | Antioxidant properties of various solvent extracts from lychee (Litchi chinenesis Sonn.) flowers[END_REF]. 250 µL of extract was mixed with 1250 µL of distilled water and 75 µL of 5% sodium nitrite (NaNO 2 ). After 6 min, 150 µL of 10% aluminium chloride (AlCl 3 ) was added. The relationship between absorbance Abs and quercetin concentration C q (μg/mL) was near linear, as following:

Abs=7.976*10 -4 C q II.15

II.3.2.16 Proanthocyanidins content

Proanthocyanidins (PAC) was determined using the vanillin assay previously described [START_REF] Sun | Critical factors of vanillin assay for catechins and proanthocyanidins[END_REF]. 0.5 mL extract was mixed with 3 mL of 4% vanillin-methanol solution and 1.5 mL HCl (37%). Absorbance was measured after 15 min of reaction in dark at 500 nm.

Catechin (Sigma-Aldrich, St-Quentin Fallavier, France) was used for the calibration curve The relationship between absorbance Abs and catechin concentration C c (μg/mL) was near linear, as following:

Abs=0.0152C c II.16

II.3.2.17 Antioxidant activity

The 2, 2-diphenyl-1-picrylhydracyl (DPPH) radical scavenging activity was used to evaluate the antioxidant capacity of polyphenols [START_REF] Nixdorf | Brazilian red wines made from the hybrid grape cultivar Isabel: Phenolic composition and antioxidant capacity[END_REF][START_REF] Yue | Ultrasound-assisted extraction, HPLC analysis, and antioxidant activity of polyphenols from unripe apple[END_REF]. The DPPH radical scavenging activity assay was performed on the extractions following the procedure by previous described [START_REF] Truong | Phenolic acid content and composition in leaves and roots of common commercial sweetpotato (Ipomea batatas L.) cultivars in the United States[END_REF]. 50 μL extract was added into 1450 µL of DPPH solution (0.06 mM in methanol) to initiate the reaction.

After a reaction time of 30 min in dark at room temperature, the reaction had reached completion. The decrease in absorbance of DPPH free radicals was read at 515 nm against methanol as a blank using a UV/Vis instrument. Trolox (0, 25, 50, 100, 250, 500 and 1000 mM/L) was used as a standard antioxidant compound for the calibration curve (Fig. II.9). The antioxidant activity was reported in mmol of Trolox equivalents per litre (mM TE/L). The relationship between inhibition of the polyphenols against the free radical DPPH In (%)

and trolox concentration C t (mM/L) was near linear, as following:

In=0.099C t II.17

II.3.2.18 Hydrogen peroxide content

The measurement for the concentration of hydrogen peroxide, H 2 O 2 , was determined by the method previously proposed [START_REF] Allen | Decomposition of water and Aqueous solutions under mixed fast neutron and $γ$-radiation[END_REF]. The method was based on the oxidation The relationship between absorbance Abs and H 2 O 2 concentration C h (10 -4 mg/L) was near linear, as following:

Abs=1.374*10 3 C h II.18

II.3.2.19 The phenolic stability

The determination of phenolic compounds was performed using a Waters 717 HPLC (Waters, France), equipped with Millenium 32 software, a degasser, a binary gradient pump, a

Waters 717 plus thermoautosampler, a column oven, and a Waters 996 diode array detector.

The separation was carried out with an Aqua C18 column (150 × 4.6 mm; 0.5 μm particle size) (Hypersil Gold, Torrance, CA, USA) at 30 °C. The elution gradient was performed according to the previous method with some modifications [START_REF] Boussetta | Valorisation of grape pomace by the extraction of phenolic antioxidants: application of high voltage electrical discharges[END_REF]; the column was initially equilibrated with distilled water and acetic acid (98:2) as solvent A for x min.

Polyphenols were eluted with a three-stage linear gradient: from 92 to 76% of A in 20 min, from 76 to 60% of A in 10 min, and from 60 to 0% of A in 15 min with a flow rate of 1 mL/min. Acetonitrile and distilled water (98:2) was used as solvent B. Absorbance of mixture was measured at 280 nm. HPLC peaks were identified on chromatograms according to their retention times and their UV-visible spectra by comparison with available standard polyphenol compounds. 60 mg gallic acid, 8mg quercetin-3-O-glucoside, and 30 mg catechin were dissolved in 20 mL 10% acetonitrile aqueous solution at different pH (4.26, 5.47, 5.79, 5.91 and 5.93), respectively. Quantification was performed by reporting the measured integration area in the calibration equation of the corresponding standard. Phenolics degradation was calculated with C/C 0 , C was the phenolic content in different pH and C 0 is the initial content of gallic acid, quercetin-3-O-glucoside and catechin in 10% acetonitrile aqueous solution at pH=5.25, 3.54 and 4.17, respectively (4 mg/mL, 0.4 mg/mL and 1.5 mg/mL, respectively).

II.3.2.20 Protein content

The concentration of proteins was determined by means of Bradford method [START_REF] Bradford | A rapid and sensitive method for the quantitation of microgram quantities of protein utilizing the principle of protein-dye binding[END_REF]. The details of analysis were presented in Technical Bulletin for Bradford Reagent (B 6916, Sigma-Aldrich). Seven standard solutions with various BSA (Bovine Serum Albumin) concentrations (0-25 μg/mL) were prepared for standard curve. 1 ml of distilled water, 0.8 mL of Bradford reagent and 0.2 mL of diluted sample (distilled water for blank) were introduced into the tube successively, the mixture was mixed with a Vortex, and the absorbance was measured at 595 nm, then the concentration of protein was calculated using the standard curve (Fig. II.11). The results were also expressed as mg/mL. The ionic, Z i , and total polyphenol, Z tf , extraction indexes respectively [START_REF] Boussetta | Extraction of valuable biocompounds assisted by high voltage electrical discharges: a review[END_REF][START_REF] Vorobiev | Pulsed-electric-fields-induced effects in plant tissues: fundamental aspects and perspectives of applications[END_REF], are defined as

Z i =(σ US -σ U )/ (σ FT -σ U ) II.20
Z tf =(P US -P U )/ (P FT -P U ) II.21

Here, lower case symbols correspond to the ultrasound-assisted (US) and control extraction experiments with untreated (U) and frozen-thawed (FT).

II.4.2 Cell disintegration index

The cell disintegration was analyzed using the confocal laser scanning microscopy (CLSM)

analysis performed with a ZEISS LSM 710 (ZEISS, Oberkochen, Germany). A single line excitation and multiple channel emission technique were used. For visualization of multispectral image data, the different channels were associated with a colors value on the display system. The RGB-color mode with three primary display colors (red, green and blue) was used. UV excitation was used with laser line at 405 and 488/543 nm, the fluorescence channel was given by the band pass filter (BP) 410-495 nm (blue), BP 495-564 nm (green) and longpass filter (LP) 563-685 nm (red).

The laser-induced fluorescence images from fruit peel samples were taken with a cooled, integrating CCD camera (AT 200) mounted on a ZEISS LSM 710 microscope with an HBO 50 excitation lamp (Zeiss, Oberkochen, Germany). Samples were detected under identical conditions and with identical buffer solutions. Single x-y images as well as a series of x-z images were taken from all samples (image size x*y*z was 212.55 μm*212.55 μm*13.63 μm), and the magnification times of images were 40. Processing of the CLSM images and calculation of cell damage degree were done using the wholly automatic procedure supported with Matlab (Version 2011a, the Mathworks Inc., Mass, USA). Figure II.13 shows the scheme applied for the processing and calculation of cell damage degree.

The following 5 steps were applied:

1) Pre-processing. For better identification of the cell walls the RGB image was transformed into the blue image. To reduce possible noise, the median-filtering technique (a special case of filter called rank-statistic filter), which allowed the edges to be preserved while filtering out the peak noise, was used [START_REF] Du | Correlating shrinkage with yield, water content and texture of pork ham by computer vision[END_REF].

2) Segmentation. To remove background, the blue image was transformed into the gray level image and then to the binary image (called bi-level images, BW). The Otsu algorithm for edge detection is used and the threshold value was determined with by Sobel filter [START_REF] Otsu | A threshold selection method from gray-level histograms[END_REF].

This filter is used in image processing for creation image emphasizing edges. It is based on the gradient approximation and convolving the image with a small, separable, and integervalued filter.

3) Inversion and holes filling. The BW image was inverted, white became black, and black became white. Now, the black and white parts present cell walls and cell bodies, respectively.

Then hole filling using a flood filling operation was applied [START_REF] Soille | Morphological image analysis: principles and applications[END_REF]. The flood filling operation is performed recursively on all elements connected to the node of interest.

4) The edges of cell image were smoothed by eroding the image with opening and closing algorithms. Opening is erosion followed by dilation, closing is a dilation followed by erosion [START_REF] Roushdy | Comparative study of edge detection algorithms applying on the grayscale noisy image using morphological filter[END_REF].

5) Corresponding pixels of each cells were found based on eight nearly label algorithm [START_REF] Charbit | Digital signal and image processing using MATLAB[END_REF]. In this algorithm, the label of a pixel is influenced by the labels of its eight nearest neighboring pixels.

6) Calculation of cell numbers and determination of damage degree. To calculate the total number of cells, N t , all the cells including the cells with incomplete edges (damaged cell walls)

were labeled, except the cells on the image borders. The number of pixels in every labeled cell and the average number of pixels in all labeled cell were calculated. To calculate the number of damaged cells, N d , the cells with number of pixels smaller than the average value wereregarded as damaged cells. The damage degree is evaluated as:

d=N d /N t II.22
Finally, the cell disintegration index, Z m , is calculated as:

Z m =(d US -d U )/ (d FT -d U ) II.23
Here, lower case symbols correspond to US, U and FT experiments.

II.5 Statistical analysis

All experiments and measurements of characteristics were repeated at least in triplicate.

The mean values and the standard deviations were calculated. All experiments and measurements were repeated at least in triplicate. Data were expressed as mean ± standard deviation. A probability value (p value) of less than 0.05 was considered statistically significant. The error bars in figures correspond to the standard deviations. TableCurve 2D® (Systat Software Inc.) was used for data fitting.

Chapter III Selectivity of polyphenols extraction III.1 Introduction

Nowadays, the ultrasound-assisted extraction (UAE) is widely recognized as a green technique for recovery of polyphenols from apple products (Chemat et al., 2017a(Chemat et al., , 2017b;;[START_REF] Jacotet-Navarro | Towards a "dry" bio-refinery without solvents or added water using microwaves and ultrasound for total valorization of fruit and vegetable by-products[END_REF][START_REF] Khadhraoui | Histo-cytochemistry and scanning electron microscopy for studying spatial and temporal extraction of metabolites induced by ultrasound. Towards chain detexturation mechanism[END_REF][START_REF] Lohani | Application of the pulsed electric field to release bound phenolics in sorghum flour and apple pomace[END_REF][START_REF] Pingret | Lab and pilot-scale ultrasound-assisted water extraction of polyphenols from apple pomace[END_REF][START_REF] Virot | Towards the industrial production of antioxidants from food processing by-products with ultrasoundassisted extraction[END_REF]. In this chapter of thesis, the extraction of polyphenols from apple flesh, peel and pomace was studied using conventional aqueous extraction (CE), ethanol concentration, solid/liquid ratio, extraction time, ultrasound power and treatment time (Chemat et al., 2017b;[START_REF] Pingret | Lab and pilot-scale ultrasound-assisted water extraction of polyphenols from apple pomace[END_REF][START_REF] Virot | Towards the industrial production of antioxidants from food processing by-products with ultrasoundassisted extraction[END_REF][START_REF] Yue | Ultrasound-assisted extraction, HPLC analysis, and antioxidant activity of polyphenols from unripe apple[END_REF]. However, the effects of CE and UAE protocols, and ethanol concentration on selectivity of polyphenols extraction from apple products were not previously discussed. Therefore, the selectivity of extraction of phenolic contents from apple products is interesting to be carried out for the purpose of:

1) Comparing efficiency and selectivity of aqueous extraction of soluble matter and phenolic contents from apple flesh for CE and UAE;

2) Analyzing the effects of pulsed ultrasonic treatment on the extraction of soluble matter, catechin and total polyphenols from the different parts (flesh and peel) of green and red apples;

3) Investigating the effects of ultrasound treatment time (0-30 min) and concentration of ethanol (0-50%) on the extraction of phenolics from apple pomace;

4)

The precise determination of catechin in extracts with the fluorescence technique.

III.3 Article II Selectivity of ultrasound-assisted aqueous extraction of valuable compounds from flesh and peel of apple tissues

Summary

Apples contain a rather high level of phenolic compounds and especially chlorogenic acid [START_REF] Podsędek | Compositional characterisation of some apple varieties[END_REF]. However, the contents and composition of polyphenols are rather different in dependence of sort of plant, variety, environmental and post-harvest factors as well as the plant part (flesh, peels, seeds and residues) [START_REF] Heimler | Plant polyphenol content, soil fertilization and agricultural management: a review[END_REF][START_REF] Oszmiański | Effect of pectinase treatment on extraction of antioxidant phenols from pomace, for the production of puree-enriched cloudy apple juices[END_REF]. Meanwhile, the mechanism of the extraction selectivity of these polyphenols with UAE is still unclear. The mechanisms induced by UAE may include the combination of many effects related to cavitation bubble collapses, fragmentation, erosion, sonocapillarity, detexturation, and sonoporation (Chemat et al., 2017b;[START_REF] Pingret | Lab and pilot-scale ultrasound-assisted water extraction of polyphenols from apple pomace[END_REF][START_REF] Saleh | Comparison of conventional and ultrasonically assisted extractions of pharmaceutically active compounds from Salvia officinalis[END_REF].

It can be speculated that manifestation of these effects is quite different in dependence on the structure of flesh and peel tissues, the ability of their swelling and rehydration, and the initial period of UAE and subsequently CE. Previous studies presented that ultrasound has an impact on the structural properties of vegetable tissue and may influence on the solute diffusivity in the tissue matrix (Chemat et al., 2017b;[START_REF] Vinatoru | An overview of the ultrasonically assisted extraction of bioactive principles from herbs[END_REF]. The observed differences in the catechin recovery from peels of green and red apples can reflect their different structure. Increasing of W resulted in increase of both the final values of C m and TPC m . However, the different branches collecting the data for protocols were observed for flesh and peel tissues. It can be due to the different mechanisms of phenolic compounds extraction from flesh and peel tissues. The obtained data evidence that selectivity of catechin extraction (R=C m /TPC m ) was depended on the type of the tissue (flesh or peel), apple variety (green or red) and applied ultrasound protocols.

III.4 Article III Effects of ultrasound treatment and concentration of ethanol on selectivity of phenolic extraction from apple pomace

Summary

Content of phenolics in the apple pomace is much higher than in apple juice or apple flesh (Wolfe et al., 2003), and it can vary among different varieties of apples [START_REF] Kalinowska | Apples: content of phenolic compounds vs. variety, part of apple and cultivation model, extraction of phenolic compounds, biological properties[END_REF]. Apple pomace (peels, mesh, seeds, cores and stems) accounts for 25%-35% of the dry mass of apple [START_REF] Gullón | Evaluation of apple pomace as a raw material for alternative applications in food industries[END_REF]. This waste is considered as a potential source of food antioxidants, phenolics [START_REF] Reis | Apple pomace as a potential ingredient for the development of new functional foods[END_REF] and as food additives to obtain a fibre riched product [START_REF] Lu | Sensory and physical quality characteristics of bread fortified with apple pomace using fuzzy mathematical model[END_REF]. Extraction of phenolics from apple pomace have attracted great attention for researchers (Ćetković et al., 2008). The potential towards the use of the UAE on a commercial scale for extraction of polyphenols from apple pomace has been demonstrated in the previous studies (Jacotet [START_REF] Jacotet-Navarro | Towards a "dry" bio-refinery without solvents or added water using microwaves and ultrasound for total valorization of fruit and vegetable by-products[END_REF][START_REF] Pingret | Lab and pilot-scale ultrasound-assisted water extraction of polyphenols from apple pomace[END_REF][START_REF] Virot | Towards the industrial production of antioxidants from food processing by-products with ultrasoundassisted extraction[END_REF]. studied (Chemat et al., 2017b[START_REF] Chemat | Applications of ultrasound in food technology: processing, preservation and extraction[END_REF][START_REF] Khan | Ultrasound-assisted extraction of polyphenols (flavanone glycosides) from orange (Citrus sinensis L.) peel[END_REF][START_REF] Pingret | Lab and pilot-scale ultrasound-assisted water extraction of polyphenols from apple pomace[END_REF][START_REF] Rajha | A comparative study of physical pretreatments for the extraction of polyphenols and proteins from vine shoots[END_REF].

Fewer studies are focused on the understanding of mechanisms leading to antioxidant polyphenol extraction enhancement due to the use of ultrasound (Chemat et al., 2017b;[START_REF] Mason | Applied sonochemistry: the uses of power ultrasound in chemistry and processing[END_REF][START_REF] Suslick | Applications of ultrasound to materials chemistry[END_REF].

Cavitation phenomenon generated by ultrasound treatment is widely regarded as the most important impact to increase extraction of valuable components (Chemat et al., 2017b;[START_REF] Mason | Applied sonochemistry: the uses of power ultrasound in chemistry and processing[END_REF]. The cavitation phenomenon resulting from bubble collision can damage cell membranes of samples [START_REF] Chemat | Comparison of conventional and ultrasound-assisted extraction of carvone and limonene from caraway seeds[END_REF], accelerate heat and mass transfer by disrupted cell walls of samples, and release the target compounds into the solvent (Roselló- Soto et al., 2015b). The shockwaves and mixing phenomena produced by cavitation can lead to increasing solid-liquid extraction yield. Bubbles explosion and shockwaves in solid/liquid mixtures can result in the fragmentation of biological particles, cell structure damage and cell membrane sonoporation [START_REF] Suslick | Applications of ultrasound to materials chemistry[END_REF]. Particles fragmentation and cells destruction can increase effective surface area for solutes extraction. In addition, cavitation induces mass transfer improvement with increasing the depth and velocity of penetration of liquid into canals and pores [START_REF] Malykh | On sonocapillary effect[END_REF][START_REF] Mason | Some neglected or rejected paths in sonochemistry--a very personal view[END_REF]. Furthermore, previous studies have shown that cavitation would produce large amounts of heat and effectively improve convective heat transfer coefficient [START_REF] Lima | Influence of Fluid Rheological Properties and Particle Location on Ultrasound-assisted Heat Transfer between Liquid and Particles[END_REF][START_REF] Sastry | Effect of Ultrasonic Vibration on Fluid-to-Particle Convective Heat Transfer Coefficients[END_REF], which result in the extraction of the target compounds into the solvent [START_REF] Singh | Introduction to food engineering[END_REF]. Therefore, the cavitation phenomena produced by ultrasound leading to polyphenol extraction enhancement is interesting to be carried out for the purpose of:

IV.3 Article V Effect of CO2 concentration in gas water solvent on the polyphenols extraction from apple skins by ultrasound

Summary

Cavitation bubbles generated by ultrasound are formed from gas dissolved in the liquid [START_REF] Ashokkumar | The characterization of acoustic cavitation bubbles--an overview[END_REF]. Dissolved gas in the solvents will influence the efficiency of UAE by affecting cavitation phenomenon [START_REF] Leong | Apple and pear peel and pulp and their influence on plasma lipids and antioxidant potentials in rats fed cholesterol-containing diets[END_REF]. Gases dissolve into the solvent can act as nuclei for a new cavitation bubble [START_REF] Mason | Applied sonochemistry: the uses of power ultrasound in chemistry and processing[END_REF]. When bubble size reaches a critical value, they will collapse near and onto the surface of a solid material result in fragmentation of friable materials, localized erosion, overall enhanced reactivity in the solvent and an increased mass transfer [START_REF] Suslick | Applications of ultrasound to materials chemistry[END_REF]. Therefore, in the second part of this chapter (details are presented in article V Effect of CO 2 concentration in gas water solvent on the polyphenols extraction from apple peels by ultrasound), the effect of the carbon dioxide (CO 2 ) concentration in gas water solvent on the polyphenols extraction efficiency introduced by ultrasound was studied.

The apple peels were extracted with gas water solvents at different CO 2 concentration (0-

IV.4 Conclusions

Chapter IV is focused on the cavitation phenomena generated by ultrasound treatment. The effects of ultrasound treatment on cell damage (cell wall disintegration index, Z m ) and extraction of valuable components (ionic, Z i , and total polyphenol, Z tp , indexes in extracts) from fruit peels (apple, banana and persimmon) were analyzed. In addition, the influence of the carbon dioxide (CO 2 ) concentration in gas water solvents on ultrasound-assisted extraction of polyphenols, including total polyphenol content (TPC), total flavonoid content (TFC), and proanthocyanidins content (PAC), from apple peels was studied. Based on the observation of the behavior of Z i , Z tp , and Z m indexes, US could damage cell membranes (sonoporation) and rupture cell walls. Furthermore, the efficiency of extraction of valuable components (Z i and Z tp ) was depended upon the value of Z m . For the extraction of ionic and polyphenol components, the linear relation between Z i and Z m was obtained for all fruit peels (apple, banana and persimmon). However, the relation of Z tp and Z m remained linearly unique for banana and persimmon peels not for apple peels. The obtained results demonstrated that cavitation phenomena generated by ultrasound could increase the extraction of valuable components from apple peels. This was because cavitation phenomena damaged cell membranes of samples and accelerated heat and mass transfer by disrupted cell walls of samples. In addition, gas water solvents could enhance cavitation phenomena to improve polyphenols extraction efficiency from apple peels. The reason was that CO 2 gases dissolved into the water solvent could act as nuclei for producing cavitation bubble by ultrasound. The experimental results found that the ultrasound treatment with CO 2 concentration in gas water solvent at 5.28 mmol/L was optimal for polyphenols (TPC, TFC, and PAC) extraction.

Ultrasonic treatment can effectively intensify the extraction of polyphenols from apple products. However, in order to obtain higher concentration of polyphenols, purification process using different technologies following extraction will be needed.

Chapter V Purification of Polyphenols in Extracts V.1 Introduction

After extracting polyphenols from apple products, purification of extracted polyphenols is commonly required [START_REF] Peng | Preparation of graphene oxide-cotton fiber composite adsorbent and its application for the purification of polyphenols from pomegranate peel extract[END_REF]. The purification methods for apple polyphenols are mainly organic solvent extraction, precipitation and crystallization [START_REF] Dai | Plant phenolics: extraction, analysis and their antioxidant and anticancer properties[END_REF][START_REF] Farías-Campomanes | Production of polyphenol extracts from grape bagasse using supercritical fluids: yield, extract composition and economic evaluation[END_REF][START_REF] Nawaz | Extraction of polyphenols from grape seeds and concentration by ultrafiltration[END_REF][START_REF] Turkmen | Effects of extraction solvents on concentration and antioxidant activity of black and black mate tea polyphenols determined by ferrous tartrate and Folin--Ciocalteu methods[END_REF]. However, these methods are relatively complex, long production cycles, high cost, and not environmentally friend. Recently, adsorption/desorption method using resin adsorbents and membrane technique (especially ultrafiltration and microfiltration) have been widely used for purification of extracted polyphenols from apple products [START_REF] Borneman | Selective removal of polyphenols and brown colour in apple juices using PES/PVP membranes in a single ultrafiltration process[END_REF][START_REF] Liu | Comparative study of ultrasoundassisted and conventional stirred dead-end microfiltration of grape pomace extracts[END_REF][START_REF] Sun | Simultaneous separation and purification of total polyphenols, chlorogenic acid and phlorizin from thinned young apples[END_REF][START_REF] Youn | Effective clarifying process of reconstituted apple juice using membrane filtration with filter-aid pretreatment[END_REF][START_REF] Zhu | Study of rotating disk assisted dead-end filtration of chicory juice and its performance optimization[END_REF], because of their advantages as few chemical substance addition, easy recycling, simple operation and easy to be realized on a large scale. The aim of this chapter is to investigate filtration of apple peel extracts for polyphenols purification.

discussed. The studies of desorption revealed the optimum desorption efficiency of polyphenols at 50% concentration of ethanol. Meanwhile, the desorption ratio, D, was positively affected by the sonication during the adsorption step. The significant higher adsorption/desorption efficiency (recovery) for polyphenols was observed with ultrasound treatment compared with the efficiency without ultrasound treatment. The highest adsorption/desorption efficiency (recovery) was observed for polyphenols as compared with proteins and soluble matter content, and it reached of about 30.6% (0 W) and about 68.9% (50 W) in absence and presence of sonication, respectively. The obtained data evidenced on a good perspective of application of adsorption/desorption procedure assisted by sonication for purification of polyphenols from apple peel extracts.

V.3 Article VII Purification of polyphenols from apple skins by membrane electro-filtration: Effects of pore size, pressure and applied voltage

Summary

In the second part of this chapter, dead-end electro-filtration with membranes was used to filtrate apple peel extracts (details are presented in article VII Purification of polyphenols from apple skins by membrane electro-filtration: Effects of pore size, pressure and applied voltage). In recent years, membrane technique has been widely used for purification of extracted polyphenols from apple products [START_REF] Borneman | Selective removal of polyphenols and brown colour in apple juices using PES/PVP membranes in a single ultrafiltration process[END_REF][START_REF] Vladisavljević | Permeate flux and fouling resistance in ultrafiltration of depectinized apple juice using ceramic membranes[END_REF][START_REF] Zárate-Rodríguez | Effect of membrane pore size on quality of ultrafiltered apple juice[END_REF][START_REF] Zhao | The effect of apple cider characteristics and membrane pore size on membrane fouling[END_REF], such as recovering the polyphenols from apple juice in the dead-end mode [START_REF] Borneman | Selective removal of polyphenols and brown colour in apple juices using PES/PVP membranes in a single ultrafiltration process[END_REF] and from apple cider in the crossflow mode [START_REF] Zhao | The effect of apple cider characteristics and membrane pore size on membrane fouling[END_REF]. However, membrane fouling can introduce changes in permeate and retentate quality [START_REF] Ulbricht | Fouling in microfiltration of wine: the influence of the membrane polymer on adsorption of polyphenols and polysaccharides[END_REF] as well as reduce the efficiency of purification of polyphenols [START_REF] Cai | Effects of ultrasound on ultrafiltration of Radix astragalus extract and cleaning of fouled membrane[END_REF][START_REF] Duclos-Orsello | A three mechanism model to describe fouling of microfiltration membranes[END_REF][START_REF] Jaffrin | Dynamic shear-enhanced membrane filtration: a review of rotating disks, rotating membranes and vibrating systems[END_REF][START_REF] Rai | Resistance in series model for ultrafiltration of mosambi (Citrus sinensis (L.) Osbeck) juice in a stirred continuous mode[END_REF][START_REF] Wakeman | Additional techniques to improve microfiltration[END_REF] during conventional membrane filtration procedures.

The "force field-assisted methods" (including electrical, magnetic and sonic forces) have received much attention as novel techniques to modify the filtration performance and prevent fouling [START_REF] Chen | Study of the influence of the electric field on membrane flux of a new type of membrane bioreactor[END_REF][START_REF] Wakeman | Additional techniques to improve microfiltration[END_REF]. The influence of electric field on the process of membrane filtration was studied [START_REF] Liu | A study on critical electric field strength of electromembrane filtration for low concentration suspension[END_REF][START_REF] Tarleton | The role of field-assisted techniques in solid/liquid separation[END_REF]. However, most previous studies in the field were focused on the reduction of membrane fouling and improvement of membrane flux.

Therefore in this part, not only the influences of membrane pore size (d m =3.02-50 nm), transmembrane pressure (∆P=1-6 bar) and direct current (DC) voltage (U=5-15 V) on the purification behaviour, and compositions changes after filtration were investigated, but also the influence of electro-filtration parameters on the selectivity of polyphenols purification in membrane processes was discussed. This work studied the performance of the membrane electro-filtration process for separation of polyphenols extracted from apple peels. The potential of low voltage DC electro-filtration for improvement quality of apple peel extracts was also discussed. The sieving ratio R (total polyphenols R tf , proteins R pr , total solutes R ts , colour intensity R I ) of filtrates with different transmembrane pressures, different membrane pore sizes, different DC voltages was calculated. The obtained data from membrane electrofiltration experiment evidenced that the sieving ratio R (R tf , R pr , R ts and R I ) of filtrates almost linearly increased with the increase of transmembrane pressure. Utilization of ultrafiltration membrane with small size of pores (UH030, d m =4.35 nm) allowed effective rejection of proteins. In addition, the rejection of proteins was observed in the anode (+) space and the most significant effect was observed at the DC voltage of 5 V. Such effects were attributed to the large size of protein molecules and their positive charges. In addition, for polyphenols the value of the sieving ratio R tf changed a little with d m , and the DC filtration allowed the purification of polyphenols in the anode (+) space and obtaining larger volume of filtrates.

The obtained data evidenced the possibility of selective purification of polyphenols compared with proteins with membrane electro-filtration.

V.4 Conclusions

As discussed in Chapter V, the efficiency of polyphenols purification from apple peel extracts with adsorption/desorption process using ultrasound and with membrane electrofiltration was evidenced.

For polyphenols purification with adsorption/desorption process, the effects of temperature (T=25-40 o C) and ultrasound intensity (P=0-400 W) on adsorption capacity were studied. In addition, the effect of ethanol concentration (C et =0-96%) in solution on desorption ratio was analyzed. The obtained results showed that the sonication during the adsorption step could significantly facilitate adsorption kinetics, increase adsorption capacity and activation energy of polyphenols adsorption, improve the desorption ratio and decrease purification time. The highest recovery of polyphenols in extracts reached 68.9 % with adsorption using ultrasound (P=50 W) and with desorption in aqueous ethanol solution at the concentration of ethanol (C et =50%).

For polyphenols purification with membrane electro-filtration, the influence of membrane pore size (d m =3.02-50 nm), transmembrane pressure (∆P=1-6 bar) and direct current (DC) electric field (U=5-15 V) on the purification efficiency was investigated. It was demonstrated that UH030 membrane used for DC electro-filtration prevents proteins passage to permeate.

In addition, electro-filtration under DC voltage of 5 V and pressure of 6 bar permitted reduce filtration time and increase filtration flux. With this process parameters, effective purification of polyphenols (99.87%) compared with proteins from apple peel extracts was attained.

Obtained results evidenced a good efficacy of adsorption/desorption process assisted by sonication for polyphenols purification from apple peel extracts. Selective purification of polyphenols from apple peels with membrane electro-filtration was also demonstrated.

General conclusion and prospects

Polyphenols of apple products are usually extracted with organic solvent, which leads environmental pollution and complicates extracts purification. Moreover, conventional extraction and purification technologies are time and energy consuming.

This thesis is devoted to the study of polyphenols extraction from apple products (apple flesh, peels and pomace) using ultrasound, and to the process optimization. The subsequent purification of polyphenols from apple peel extracts by adsorption/desorption and membrane filtration were also investigated.

The obtained results demonstrated that ultrasound can significantly increase extraction yields of total polyphenols and catechin compared to conventional extraction (CE).

Interestingly, ultrasound assisted extraction (UAE) permitted more selective polyphenols recovery. The selectivity of catechin extraction (R) was depended on the type of apple tissue (flesh, peel or pomace), apple variety (green or red), extraction temperature, UAE protocols, and ethanol/water ratios. For studied apple products, the values of R were noticeably higher using UAE as compared to CE. For apple flesh and peels, the value of R was nearly constant for flesh of red apples (R=19%), and peel of green apples (R=16%). However for flesh of green apples and peel of red apples, the value of R was dependent on the ultrasound protocols.

For apple pomace, using the UAE with low intensity and short duration leaded to more selective extraction of catechin (R15-31%). However, using intensive UAE and extraction in ethanol/water solution (concentration of ethanol, C et =50%) resulted in a high level of TPC (850mg/100g DM) and lower content of catechin (R2%).

The cavitation phenomena generated by ultrasound contribute to increase extraction of valuable components from fruit peels. Cavitation bubbles damaged cell tissue and accelerated heat and mass transfer. Cavitation phenomena were analysed in terms of the behavior of ionic solutes Z i , total polyphenols, Z tp , and cell disintegration Z m indexes. The values of Z i and Z tp depended on the values of Z m and presented linear relationship for banana and persimmon peels, while these dependencies were nonlinear for apple peels. In addition, the gas water solvents (CO 2 with concentration of 5.28 mmol/L) increased the extraction yields of polyphenols (TPC, total flavonoid content and proanthocyanidins content) by enhancing cavitation phenomena. The produced cavitation effect may increase the water absorption by samples, which contributes to better phenolics extraction.

Adsorption/desorption procedure using the polyaromatic amberlite adsorbent XAD-16 and assisted by sonication was beneficial for the purification of polyphenols from apple peel extracts. The isotherm of polyphenol adsorption was well fitted using the Freundlich model.

The adsorption kinetics was fitted with stretched exponential law. The data on adsorption kinetics and static isotherm evidenced the presence of adsorption on heterogeneous surface with a broad distribution of adsorption times that can depend on content of polyphenols in the solutions and applied power of sonication. Moreover, the obtained results showed that the sonication during the adsorption step could significantly facilitate absorption kinetics, increase adsorption capacity and decrease adsorption time. The studies of desorption process revealed the optimum desorption efficiency of polyphenols at ethanol concentration of 50%.

The desorption ratio was positively associated with the sonication during the adsorption step.

After adsorption and desorption processes, the highest recovery of polyphenols in apple peel extracts reached 68.9 % with sonication.

Dead-end electro-filtration with DC voltage of 5 V and pressure of 6 bar permitted effectively prevent proteins from passing through ultrafiltration membrane UH030 with size of pores (d m =4.35 nm). The sieving ratio of total polyphenols, R tp in filtrate increased linearly with the increase of transmembrane pressure and was independent from membrane pore size.

This process permitted better purifying of polyphenols. The results obtained from this thesis raise some new questions and suggest some future prospects:

1. For the extraction:

1) Conduct a study on the combination of US with different treatment techniques (such as microwaves (MW), pulsed electric field (PEF), high voltage electrical discharges, supercritical CO 2 , etc.) to find an optimal protocols of bio-compounds extraction from apple peels. For instance, MW application permits rapid heating the samples, which is beneficial to faster solvent penetration into samples, migration of dissolved molecules and better solubility of bio-compounds. As a consequence, US and MW can produce a synergistic effect for the extraction of bio-compounds.

2) Deepen investigation of different effects of US treatment, such as capillarity, detexturation, tissue fragmentation, local shear stress, sonocapillary effect and sonoporation.

Cavitation phenomenon generated by ultrasound is often considered as a most important for plant tissue damage increasing extraction yield. However, during US-assisted extraction, other phenomena intensifying bio-compounds recovery occur, which needs their analysis.

3) Design an efficient ultrasound-assisted large-scale extraction with high extraction yields and low energy consumption for applications in industry.

2. For the purification:

1) Better understanding of phenolics adsorption/desorption mechanisms with resins is still needed.

2)

A combination of US and other methods to improve the efficiency of purification during adsorption/desorption process will be interesting. For instance, US technology may be combined with vapour pressure and external electrostatic field.

3) Circulation and controllable temperature in membrane electro-filtration method need to be studied. During the membrane electro-filtration, the electrode chamber can be continuously flushed by circulating tap water. Although the flowing tap water can implement circular filtrating and keep a constant temperature, the tap water leads to the dilution of extracts and further decrease purification ratio. Therefore, it is significant to find solutions to implement circular membrane electro-filtration.

I

  .4.2.1 Introduction ................................................................................................................ I.4.2.2 Operational parameters influencing adsorption and desorption ............................... I.4.2.3 Application of adsorption and desorption for polyphenols purification .................... I.4.3 Membrane filtration .............................................................................................................. I.4.3.1 Classification of membrane filtration ........................................................................ I.4.3.2 Materials of filtration membranes ............................................................................. I.4.3.3 Models of membrane filtration ................................................................................... I.4.3.4 Application of membrane filtration ............................................................................ I.4.3.5 Membrane electro-filtration .......................................................................................

  matter ............................................................................................................................ II.3.2 Analysis of extracts ..............................................................................................................II.3.2.1 Soluble matter content ......................................................................................

  analyses ........................................................................................................... II.4.1 Extraction indexes................................................................................................................ II.4.2 Cell disintegration index ...................................................................................................... II.5 Statistical analysis ........................................................................................................ Chapter III Selectivity of polyphenols extraction .................................................................. III.1 Introduction ................................................................................................................ III.2 Article I Comparison of conventional and ultrasound-assisted aqueous extraction of soluble matter and phenolic compounds from apple flesh ......................................... III.3 Article II Selectivity of ultrasound-assisted aqueous extraction of valuable compounds from flesh and peel of apple tissues .............................................................. III.4 Article III Effects of ultrasound treatment and concentration of ethanol on selectivity of phenolic extraction from apple pomace ..................................................... III.5 Conclusion .................................................................................................................. Chapter IV Cavitation Phenomenon during Ultrasound-assisted Extraction of Polyphenols .................................................................................................................................................. IV.1 Introduction ................................................................................................................ IV.2 Article IV Correlations between disintegration degree of fruit skin cells induced by ultrasound and efficiency of bio-compounds extraction ............................................ IV.3 Article V Effect of CO 2 concentration in gas water solvent on the polyphenols extraction from apple skins by ultrasound ..................................................................VI Ultrasound assisted purification of polyphenols of apple skins by adsorption/desorption procedure ....................................................................................

  Many studies have turned to improve the polyphenols extraction from apple products. Among many extraction techniques, solvent extraction and thermal extraction are the most conventional ones. However, typically, such extraction methods are not selective. They can result in decrease of purity of extracts and require supplementary separation procedures. It is therefore necessary to find a compromise between extraction yield, extract quality, separation efficiency, and consumption energy. Recently, different non-conventional extractions techniques (supercritical fluid, high pressure homogenization (HPH), ultrasound (US), microwave, high-voltage electrical discharges (HVED), and pulsed electric fields (PEP), enzymatic and other treatments) have been proposed to intensify extraction of polyphenols. Nowadays, US treatment has been widely used for polyphenols extraction from apple products. The ultrasound-assisted extraction (UAE) is widely recognized as a green technique with reduced energy consumption, and decreased processing time. Particularly, UAE also allows reduction of wastes and elimination of generation of hazardous substances.

Figure I. 2 .

 2 Figure I.2. Selected phenolic compounds in apples[START_REF] Kalinowska | Apples: content of phenolic compounds vs. variety, part of apple and cultivation model, extraction of phenolic compounds, biological properties[END_REF].

Figure I. 3 .

 3 Figure I.3. Main polyphenols constituents of apple peels (Giomaro et al., 2014).

Figure I. 4 .

 4 Figure I.4. Schema of the interaction between condensed tannins and proteins (Santos-Buelga and De Freitas, 2009).

Figure I. 6 .

 6 Figure I.6. HPLC chromatogram at 280 nm of unripe apple polyphenols extract (1, procyanidin B1; 2, (+)-catechin; 3, chlorogenic acid; 4, procyanidin B2; 5, caffeic acid; 6, (-)-epicatechin; 7, quercetin-3-D-galactoside; 8, quercetin-3-glucoside; 9, phlorizin; 10, quercetin (Yue et al., 2012).

  Front-face synchronous fluorescence spectra combined with principal component analysis (PCA) method was beneficial for the prediction of the total phenolic content (TPC=552 ± 403 mg GAE/L), flavonoid content (TFC=134 ± 69 mg CE/L), and the antioxidant activity (TAC=4.6 ± 3.8 mmol (mM)) of apple juices (Fig. I.7) (Włodarska et al., 2017).

Figure I. 7 .

 7 Figure I.7. Total synchronous fluorescence (TSyF) spectra of the apple juices: a) clear reconstituted from concentrate (TPC = 198.4 mg GAE/L, TFC = 52.7 mg CE/L, TAC = 1.06 mM), b) cloudy produced from concentrate with added apple pulp (TPC = 386.5 mg GAE/L, TFC = 153.4 mg CE/L, TAC = 4.43 mM), c) pasteurized naturally cloudy produced not from concentrate (TPC = 174.2 mg GAE/L, TFC = 54.7 mg CE/L, TAC = 1.36 mM), and d) freshly squeezed juices (TPC = 391.2 mg GAE/L, TFC = 42.2 mg CE/L, TAC = 3.05 mM)[START_REF] Włodarska | Screening of antioxidant properties of the apple juice using the front-face synchronous fluorescence References 207 and chemometrics[END_REF].

  , which is different in conventional extractions (Fig. I.8). Microwave-assisted extraction has some advantages, such as shortextraction time, low-energy requirement, high extraction efficiency and minimum degradation of target compounds

Figure

  Figure I.8. Basic heat and mass transfer mechanisms in microwave and conventional extraction of natural products (Périno-Issartier et al., 2011).

  . Nowadays, the effects of solvents, temperature, time and detergents during the extraction of polyphenolics by US and microwave-assisted extraction methods have been studied by researchers for the development of better extraction and recovery method for polyphenolics. I.3.2.2 Pulsed electric fields Pulsed electric fields (PEF) treatment is a non-thermal technique providing electrical pulses of a few microseconds. PEF action is mainly localized on a microscopic scale. Pores are formed in cell membranes thus accelerating the release of intracellular compounds into solvents. The pore could be formed on the cell membrane (electroporation) by PEF treatment (Fig. I.9). The mechanism of PEF technique can be explained by the capacitor model. The cell membrane which is composed of two lipidic layers can be represented by a capacitor. The cell cytoplasm acts as an electrical conductor. The conductivity of the extracellular media is represented by a resistor in parallel and two resistances in series. When an electric field is applied, there is charges accumulation on both sides of the membrane. The cell membrane is polarized and a trans-membrane potential (V m ) appears. Pores are formed on the membrane with V m values higher than the dielectric characteristic of the membrane. This phenomenon would be similar to the breakdown of an electrical capacitor. The advantage of PEF assistedextraction is to preserve the structure of the products and promote the purification of the subsequent extracts due to PEF results in electroporation of cell membranes but does not fragment the products.

Figure

  Figure I.9. Schematic representation of electroporation mechanism in biological cell membrane exposed to an electric field. E is the electric field intensity and E c is the critical electric field intensity[START_REF] Kumari | Recent advances on application of ultrasound and pulsed electric field technologies in the extraction of bioactives from agro-industrial by-products[END_REF].

  alter and disrupt the cells thus resulting in the fragmentation of the cells (Fig. I.10). Since HVED could damage both cell walls and cell membranes of samples. Meanwhile, HVED can produce free radicals that make very reactive environments (Grémy-Gros et al., 2009).

Figure

  Figure I.10. Types of electric discharges in an aqueous solution (a) and scheme of electrohydraulic disintegration process (b)[START_REF] Vorobiev | Enhanced extraction from solid foods and biosuspensions by pulsed electrical energy[END_REF].

Figure

  Figure I.11. The principle of ultrasound-assisted extraction[START_REF] Leong | Apple and pear peel and pulp and their influence on plasma lipids and antioxidant potentials in rats fed cholesterol-containing diets[END_REF].I.3.2.4.3 Treatment equipmentThe two main types of devises for ultrasound treatment in the laboratory are the ultrasonic bath and the ultrasound probe (Fig. I.12). Ultrasonic bath is widely used for disinfection and material cleaning whereas ultrasonic probe is generally used for extractions. The source of ultrasound power for both systems is based on a transducer, such as the piezoelectric transducer, which is one of the most common type used in the majority of ultrasonic reactors(Chemat et al., 2017b). The piezoelectric transducer has ability to deliver high powers which vary with the variation of the amplitude. The waves produced by transducer propagate mainly in axial directions and dissipate strongly in radial directions.

  [START_REF] Chukwumah | Effect of frequency and duration of ultrasonication on the extraction efficiency of selected isoflavones and trans-resveratrol from peanuts (Arachis hypogaea)[END_REF] reported a selective extraction of phenolics from peanuts with ultrasound frequency of 25 kHz. González-Centeno et al. (2014) demonstrated that 40 kHz was the most effective for the extraction of phenolics from grape pomace by comparing three frequencies (40 kHz, 80 kHz and 120 kHz).

I

  of membrane filtration Efficiency of the membrane filtration is mainly dependent on the rejection of micro-and macromolecular species (sugars, bio-molecules, polymers and colloidal particles). A membrane, as a selective barrier between two phases, can separate the feed into permeate and retentate (Fig. I.13

Figure I. 13 .

 13 Figure I.13. Schema of membrane separation process[START_REF] Tsuru | Nano/subnano-tuning of porous ceramic membranes for molecular separation[END_REF].

Figure I. 14 .

 14 Figure I.14. The applicability ranges of different separation processes based on membrane pore sizes[START_REF] Cui | Fundamentals of pressure-driven membrane separation processes[END_REF].

  hydrophobicity, pH, oxidant tolerance, strength and flexibility. At present, most common polymers used for producing polymeric membranes applied for polyphenols purification are PES and PVDF (Fig. I.15). PES is a less hydrophobic polymer because of containing more sulphur dioxide groups. While PVDF, contains an aliphatic chain with multiple carbonfluorine bonds, is more hydrophobic due to less susceptible to hydrogen bonds.

Figure I. 15 .

 15 Figure I.15. Chemical structural units of PES and PVDF[START_REF] Cassano | Effect of polyphenols-membrane interactions on the performance of membrane-based processes[END_REF].I.4.3.3 Models of membrane filtrationFiltration models are generally classified according to the flow direction of the feed. The principle of main filtration models are presented in Fig.I.16.

  Figure I.16 Principle of different filtration models. a) Dead-end filtration (Ketola, 2016), b)

  apples, and it can vary among different varieties of apples. Nowadays the extraction and purification of phenolic compounds from apple products attract great attention. The conventional method is based on a solid-liquid extraction by various solvents with damaging cell membranes to release polyphenols. The conventional extraction needs relatively long duration, high temperature, high energy consumption and the addition of organic solvents. Therefore, many alternative technologies have been emerged, such as high pressure, ultrasound, and electric technologies, to improve the polyphenols extraction process.Nowadays, the ultrasound-assisted extraction is most widely used alternative technology for polyphenols extraction from apple products. However, the impact of ultrasound-assisted extraction on the selectivity of valuable compounds recovery from apple products was not yet elucidated enough. The objective of the first part of this thesis was to selectively extract valuable compounds (especially polyphenols) from apple products with ultrasound treatment.The ultrasound treatment induces cavitation, shockwaves and mixing phenomena leading to increasing solid-liquid extraction yield. Especially, cavitation phenomenon was most important for the extraction efficiency due to the formation, growth and collapse of bubbles inside solvents. The bubbles collapse could cause the rupture of cell walls to enhance solvent contact with the available extractable cell material and accelerate diffusion. The mechanisms of cavitation phenomena produced by ultrasound need to be further understood.

Fresh

  Figure II.1 Photos of the three raw materials of apples: (a) peel; (b) flesh; (c) pomace

  20-75 °C was selected for CE in this thesis. The distilled water for extraction was preheated to specified temperature (50-75 o C). The extraction experiment with ethanol aqueous solution was all at room temperature (20 o C). The temperature during extraction was stabilized using a water thermal bath Polystat 36(Fisher Scientific, France). The total extraction time was up to 3 h.II.2.2.2 Ultrasound-assisted extraction20 g of samples were put in a glass beaker filled with 200 mL of ethanol aqueous solution (C et =0-50%), so the solid/liquid ratio was 1/10. Ultrasonic treatment of solution was done directly in the glass beaker using an ultrasonic processor UP 400S (400 W, 24 kHz, Hielscher GmbH, Stuttgart, Germany) (Fig.II.2a). The titanium ultrasonic probe (H14, Hielscher GmbH, Stuttgart, Germany) with a tip diameter of 14 mm, and the length of 100 mm was used. The ultrasonic treatment was applied in pulsed mode. The different ultrasonic powers (P=28-150 W) were selected for ultrasound-assisted extraction process. The extraction T by ultrasound with distilled water was in the range of 20-75 o C, and with ethanol aqueous solution was at room temperature (20 o C). The scheme of applied pulsed sonication treatment is illustrated in Fig. II.2b. The ultrasound treatment was done in pulsed mode with sequential application of n=1-10 ultrasonic pulses. A pause with duration of Δt w =50-1000 s was applied after each ultrasound pulse with duration of Δt u =10-180 s. In order to avoid increasing temperature by ultrasound treatment, the glass beaker was put in an ice/cold water box to keep the temperature at specified temperature. The total time of UAE was t e =n(Δt u +Δt w )=0-5050 s. (a) (b) Figure II.2 (a) The experimental ultrasound generator. (b) Scheme of applied pulsed sonication treatment. The specific input energy, W, produced by ultrasound treatment was estimated from the temperature elevation ΔT in sample using following equation: W= mC p ΔT/Δt u II.1 where m and C p (≈4.18 kJ per kg K) are the mass and specific heat capacity of solution, respectively, Δt u is the duration of sonication. In this study, W was in the range of 6.4-327.3 kW/kg. For ultrasound-assisted extraction experiments, the effects of operated parameters (C et , T, n, Δt w , Δt u , t e, P, W) on polyphenol yields were analyzed. The extracts from apple flesh and apple peels were stored at 4 ºC for further analysis. The extracts of apple pomace were firstly centrifuged for 10 min at 4000 rpm (Laborzentrifugen 3-10, SIGMA, Osterode am Harz, Germany) to separate supernatant and solid sediment before stored the supernatant at 4 ºC for further analysis. For the extracts of apple peel powders, the supernatant obtained after centrifuging extracts for 10 min at 4000 rpm was concentrated to remove the ethanol in a vacuum rotary evaporator (LABOROTA 4001, Heidolph Instrument, Schwabach, Germany) at 40 o C. Then the concentrated aqueous solution was filtrated with filter papers (No.474, VWR, Geldenaaksebaan, Leuven). Finally, the filtrate was stored at 4 ºC for further analysis. II.2.3 Polyphenols purification II.2.3.1 Adsorption/desorption procedure II.2.3.1.1 Adsorbents preparation

  Germany) at 70 o C for 24h. The final moisture content of resin was 80.39%. II.2.3.1.2 Adsorption procedure The adsorption experiments were performed at 25-40 o C in a glass beakers by mixing the adsorbent amberlite XAD-16 (2 g) with polyphenol extracts (100 mL) at different concentrations of total polyphenols, C 0 (0.01-6 mg/mL). The beakers were kept in shaking water bath SW22 (Julabo GmbH, Seelbach, Germany) at a rate of 150 rpm. The total time of adsorption experiments was up to 1440 min.

  and C f are the initial (before adsorption) and final (after desorption) concentration of bio-molecules (mg/mL), respectively. II.2.3.2 Membrane filtration II.2.3.2.1 Dead-end electrofiltration Filtration setup is presented in Figure II.3. Dead-end electrofiltration was performed with an effective membrane area of 1.809*10 -3 m 2 . For each experiment, 90 mL of feed solution was used. 4 types of hydrophilic polyethersulfone filtration membranes (Microdyn-Nadir GmbH, Germany) with MWCO of 10, 30 and 150 kDa (specific description of membranes is presented in II.1.5) were used to filtrate apple peel extracts. The new membrane was used for each set of experiments. Filtration pressure of 1, 4, 6 and 10 bar (1-10 *10 5 Pa) was supplied and continuously monitored by a pressure gauge. Electrofiltration voltage of 5, 10 and 15 V was provided by FLUKE 45 and Consort EV261. The filtrate was collected in beakers placed on an electronic balance and the mass of filtrate was recorded by computer software (Service électronique UTC, Compiègne, France).

Figure II. 3

 3 Figure II.3 Scheme presentation of dead-end electrofiltration. II.2.3.2.2 Calculated parameters The sieving ratio R was defined as ratio of different substances presented in solution after and before filtration (concentration of total polyphenols C tf , concentration of proteins C pr , concentration of total solutes C ts , and colour intensity I). The rejection coefficients of different substances are calculated as K r =1-R.

Genesys 20 ,

 20 Thermo Electron Corporation, MA, USA). Gallic acid (Sigma-Aldrich, St-Quentin Fallavier, France) was used for the calibration curve (Fig. II.4). The results were expressed as mg GAE/g DM.

Figure II. 4

 4 Figure II.4 Standard line of gallic acid concentratin for total polyphenol content analysis.

  Figure II.4 presents the calibration curve for the fluorescence of catechin in water. For calibration, the standard of catechin hydrate (≥ 0.98%, Sigma-Aldrich) was used. Figure II.4 presents the calibration curve and examples of emission spectra (inset to Fig. II.5).

Figure II. 5

 5 Figure II.5 Intensity of the fluorescence emission, I f , versus the concentration of catechin in water, C c . Inset shows examples of emission spectra at different concentrations of catechin. The relationship between fluorescence intensity I f (au) and catechin concentration C c (mg/mL) was near linear, as following: I f =7.14*10 4 C c II.13 Figure II.6 presents examples of calibration curves for the fluorescence of catechin for concentration of ethanol (C et =0 and 10 %). For relatively small concentrations of ethanol (C et ≤10%) the relationship between catechin concentration in solvent, C s (mg/mL) and fluorescence intensity I f (au) was practically linear (Fig. II.6).

Figure II. 6

 6 Figure II.6 Concentration catechin, C c , in solvents versus the fluorescence intensity I f (au) at ethanol concentrations C et =0% and C et =10%.

Finally, 500

 500 µL of 1 M sodium hydroxide (NaOH) was added and the total volume was made up to 2500 μL with distilled water. Absorbance was measured at 510 nm. Quercetin (Sigma-Aldrich, St-Quentin Fallavier, France) was used for calculating the calibration curve (Fig. II.7). Results were expressed as mg of quercetin equivalent per 100 gram of dry matter (mg/100g DM).

Figure II. 7

 7 Figure II.7 Standard line of quercetin concentratin for total flavonoid content analysis.

(

  Fig. II.8). Results were expressed as mg of catechin equivalent per 100 gram of dry matter (mg/100g DM).

Figure II. 8

 8 Figure II.8 Standard line of catechin concentratin for total proanthocyanidins content analysis.

Figure II. 9

 9 Figure II.9 Standard line of trolox concentratin for antioxidant activity analysis.

  of the iodide ion by hydrogen peroxide, which produced an adsorption peak at 350 nm proportional to the concentration of H 2 O 2 . Two reagents are used for detection, one is a solution of potassium acid phthalate of 20 g/L, the other one is a solution of 1% ammonium molybdate (0.2 g/L), sodium hydroxide (2 g/L) and potassium iodide (66 g/L). 0.3 mL of the sample was mixed with 0.75 mL of the each reagent. Absorbance was measured after 15 min in dark at 350 nm. Hydrogen peroxide, H 2 O 2 (VWR, France) was used for the calibration curve (Fig. II.10). Results were expressed as H 2 O 2 10 -4 mg/L.

Figure

  Figure II.10 Standard line of H 2 O 2 for active species analysis.

Figure

  Figure II.11 Standard line of BSA for protein concentration analysis. The relationship between absorbance Abs and BSA concentration C B (µg/mL) was near linear, as following: Abs=0.041C B II.19

Figure

  Figure II.12 presents examples of cell images for samples obtained after U (a) and US (b) extraction experiments for studied fruit peels. The data were presented for the extraction time of t e =2700 s. It corresponded to the US energy input, W=0.299 kW•h/kg in the US experiments. Cells were practically undamaged in fruit peels obtained after U experiments (Fig. II.12a), whereas in peels obtained after US experiments the spaces between cells became larger (apple), and many cells became connected together (banana and persimmon) (Fig. II.12b). Preliminary US extraction experiments with different US energy inputs (n=0-9, W=0-0.299 kW•h/kg) showed that with a higher US energy input, the cell membranes and cell walls were damaged more severely, and more cells were connected to each other, and the spaces between cells become larger.

Figure

  Figure II.12 Examples of images for samples obtained after U (a) and US (b) extraction experiments for studied fruit peels (apple, banana, persimmons).

Figure

  Figure II.13 Scheme applied for processing of the images.

Figure

  Figure II.14 presents example of temporal changes of the cell damage degree, d, in US, U and FT extraction experiments with apple peels. The obtained results presented that the damage degree, d, increased with increasing of extraction time, t e , in U and US experiments, whereas in FT experiments the damage degree was approximately 0.91.

Figure II. 14

 14 Figure II.14 Examples of temporal changes of cell damage degree, d, in US, U and FT extraction experiments for apple peels.

  ultrasound-assisted extraction (UAE) and ethanol/water extraction. The catechin content (C c ), total polyphenols content (TPC) and relative content of C c in TPC (R=C c /TPC) were evaluated. The efficiency of UAE and the extract purity can be governed by the combined action of thermal and sonication effects, different processing factors (such as temperature,

  distribution of phenolic compounds inside these tissues. Therefore, in the second part of this chapter (details are presented in article II Selectivity of ultrasound-assisted aqueous extraction of valuable compounds from flesh and peel of apple tissues), the selectivity of ultrasound-assisted aqueous extraction of phenolics from different part of apples (flesh and peel) and different varieties of apple was compared. The effects of pulsed ultrasonic treatment during initial period of extraction (first 300-350 s) on the recovery of soluble matter, catechin and total polyphenols from different parts (flesh and peel) of green (Granny Smith) and red (Red delicious) apples were studied. The different impacts of W (0-26.8 kJ/kg) on the extraction of soluble matter and catechin were observed for flesh and peel tissues. For all UAE protocols and used variety of apple (green or red), the extraction levels of o Brix, C c and TPC for peel tissue were compared with flesh tissue. The significant acceleration in extraction of o Brix and C c of apple flesh and peel for UAE was observed compared to the extraction contents for CE. The extraction levels of C c and TPC were noticeably higher for peel tissue as compared to flesh one for all UAE protocols and used variety of apple (green or red). In addition, the different impacts of W on the extraction of soluble matter and catechin were observed for flesh and peel tissues. The obtained data evidenced more significant impact of the US pretreatment on extraction of catechin as compared to extraction of total soluble matter. The o Brix values increased continuously during

  Therefore, in the last part of this chapter (details are presented in article III Effects of ultrasound treatment and concentration of ethanol on selectivity of phenolic extraction from apple pomace), the selectivity of phenolics extraction from apple pomace with ultrasound-assisted ethanol/aqueous extraction was studied. The extraction kinetics and extraction yields of C c and TPC were evaluated at different times of ultrasound treatment (t u =0-30 min) and concentrations of ethanol (C et =0-50%). The obtained results presented that the highest extraction efficiency of TPC from apple pomace was observed for t u = 30 min, C et = 50% and t e = 60 min. The relative content of catechin (R = C c /TPC) of applied extraction protocols was analyzed to demonstrate the selectivity of catechin extraction. The ratio (R = C c /TPC) was different in dependence of applied extraction protocols for apple pomace. The experimental dependence C c (TPC) for different applied protocols was fitted by power equation C c = a((TPC + 1) b -1), where a = 6.0±1.9 mg per 100 g DM and b = 0.23±0.04 are fitting parameters. The initial portions of extracts at a small level of TPC (≤50 mg per 100 DM) were richer in C c (R≈15%-31%) as compared with last portions of extracts (R≈2%) obtained using long duration UAE and extraction in concentrated ethanol/water mixtures at a high level of TPC(850 mg per 100 g). Experiment results presented simultaneous application of UAE and using of ethanol/water mixtures allow fine regulation of catechin extraction selectivity from apple pomace.III.5 ConclusionThis chapter III is focused on the intensification of polyphenols extraction from apple products (flesh, peel and pomace) with ultrasound treatment. By comparing the obtained data, the extraction yields of polyphenols from apple products obtained with ultrasound-assisted extraction (UAE) are noticeable higher than the one obtained with conventional extraction (CE). The increase of ultrasound energy, intensity and treatment time resulted in the increase of polyphenol extraction values. Moreover, the results evidenced the possibility of fine regulation of extraction selectivity using different temperatures, UAE protocols, and ethanol/aqueous mixtures. The relative content of catechin in total polyphenol content,TPC, (R) presented the selectivity in extraction of phenolic compounds from apple products. For apple flesh, significant acceleration of catechin extraction was observed at higher temperature (T) and higher ultrasound energy (W). The values of R were noticeably higher with application of UAE as compared with CE. The catechin contents were noticeably higher for peel as compared to flesh and increased with the increase of W. The values of R depend on the type of tissue (flesh or peel), apple variety (green or red) and applied treatment protocols. For apple pomace, the highest extraction efficiency of TPC was observed at ultrasound treatment time, t u =30 min, ethanol concentration, C e =50% and extraction time, t e =60 min. The initial portions of extracts at small level of TPC (50mg/100g DM) were richer in catechin (R15-31%), whereas the last portions obtained by using of intensive UAE and extraction in ethanol/water with high level of TPC (850mg/100g DM) were more exhausted in catechin (R2%). These obtained laboratory-scale results will help for the future scale-up of UAE processes. In the following, the mechanism of the observed extraction by ultrasound treatment is necessary to be studied. of antioxidant polyphenols from various food materials has been widely

  between disintegration degree of peel cells induced by US and efficiency of bio-compounds extraction from fruit peels; 3) Study of the effect of the carbon dioxide (CO 2 ) concentration in gas water solvent on the polyphenols extraction efficiency introduced by ultrasound IV.2 Article IV Correlations between disintegration degree of fruit skin cells induced by ultrasound and efficiency of bio-compounds extraction Summary In the first part of this chapter (details are presented in article IV Correlations between disintegration degree of fruit skin cells induced by ultrasound and efficiency of biocompounds extraction), cavitation phenomenon, the most important impact to increase extraction of valuable components by US treatment, was analyzed, include determination of cell wall disintegration index, Z m , different extraction indexes (ionic content, Z i , total polyphenols, Z p ), and discussion of their correlations of different fruit peels (apple, persimmon, and banana). The total time of aqueous extraction was up to t e =0-2700 s and the US specific energy inputs, W, were in the interval between 0.033 and 0.299 kW.h/kg. The ionic, Z i , and total polyphenol, Z p , extraction indexes of the liquid extracts from different fruit peels were analyzed. The Z m from microscopic images was calculated. The observed different behavior of Z i , Z p , and Z m indexes reflected different effects of cavitation phenomenon produced by US on damage cell membranes (so-called sonoporation) and rupture of cell walls. In extraction of ionic components the nearly linear Z i ,(Z m ) dependencies were observed for all fruit peels with level of extraction grow in the row apple < persimmon < banana. In extraction of polyphenols the similar nearly linear Z p ,(Z m ) dependencies were only observed for bananas and persimmons, but for apples this dependence was non-linear. Moreover, the order in a row of the level of extraction was depended upon the value of Z m . The obtained data presented that the increase of US energy input caused the increase of values of Z i , Z p and Z m and the extraction efficiencies (Z i and Z p ) were related with Z m .

  7.05 mmol/L) compared to different conventional solvents (distilled water, 10% ethanol aqueous solvent and 10% methanol aqueous solvent) without and with ultrasound treatment (W=0.242 kW•h/kg) at room temperature. The extraction of TPC and the water holding capacity of apple peels extracted in different solvents with and without ultrasound treatment were compared. The TPC, TFC, PAC, pH, electrical conductivity (σ) and antioxidant activity (DPPH) of extracts with gas water solvents at different concentration of CO 2 by ultrasound were detected. The extracted TPC and water holding capacity of apple peels both had a significant increase by ultrasound for all solvents, especially for gas water solvent. Since the cavitation phenomenon generated by ultrasound could increase the water absorption of the sample and the increase of water adsorption could subsequently contribute to the increase of extracted TPC. The CO 2 concentration in gas water solvent at 5.28 mmol/L was optimal for polyphenols (TPC, TFC, and PAC) extraction enhancement and antioxidant activity (DPPH) increase by ultrasound. Meanwhile, the pH and σ of liquid extracts increased with the increase of CO 2 concentration in gas water solvents. These results adequately explained that the CO 2 concentration in gas water solvents could influence polyphenols extraction of samples by ultrasound treatment, due to CO 2 gases dissolve into the solvent could act as nuclei for producing cavitation bubble by ultrasound, and the produced cavitation effect could finally increase polyphenol extraction of samples.

  The US-assisted extraction is able to increase the extraction yields, improve the quality of the extracts and facilitate the subsequent separation and purification processes. Application of adsorption/desorption procedure assisted by ultrasound can effectively improve the purity of polyphenols and decrease purification time. Membrane electro-filtration permits obtain selective purification of polyphenols without using organic solvents. Generally, this research work provides a better understanding of polyphenols extraction and purification with ultrasound treatment.

  II.1.1 Apple peels ..........................................................................................................................

II.1.2 Apple flesh ........................................................................................................................... II.1.3 Apple pomace ...................................................................................................................... II.1.4 Other fruit peels ................................................................................................................... II.1.5 Adsorbents ........................................................................................................................... II.1.6 Filtration membranes ........................................................................................................... II.2 Extraction and purification experiments .................................................................. II.2.1 Sample preparation .............................................................................................................. II.2.2 Polyphenols extraction ......................................................................................................... II.2.2.1 Conventional extraction ................................................................................... II.2.2.2 Ultrasound-assisted extraction ........................................................................ II.2.3 Polyphenols purification ...................................................................................................... II.2.3.1 Adsorption/desorption procedure ..................................................................... II.2.3.1.1 Adsorbents preparation .......................................................................................... II.2.3.1.2 Adsorption procedure ............................................................................................ II.2.3.1.3 Desorption procedure .............................................................................................

II

electrofiltration ...................................................................................... II.2.3.2.2 Calculated parameters ............................................................................................

  The phenolic stability ...................................................................................... II.3.2.20 Protein content ............................................................................................... II.4 Indexes

Table I

 I

		.1. The utilizations of apple peels
	Application	Examples	References
	Direct use	Animal feed, compost, source of
		dietary fiber in bakery products,
		press aid in fruit juice preparation.

Table I .

 I 2. The valorisations of apple peels[START_REF] Massini | Polyphenol content and antioxidant capacity of apple fruit: effect of cultivar and storage conditions[END_REF]

	Peel	Preservation	Extraction	Applications	Target	References
	materials	conditions	solvent		compounds
	Bulk peel powders	Drum-drying	70% Acetone (v/v)	Fibre Functional foods formulation	Dietary fibre; compounds phenolic	(Henríquez et al., 2010)
		1) Water		Fibre	Dietary fibre;	(Rupasinghe et al.,
		blanching		formulation	phenolic	2008)
		2) Oven-drying (60°C,	Methanol	Functional foods	compounds
		with air
		circulation)
		1) Water	80%		Phenolic
		blanching;	Acetone;		compounds
		ascorbic acid	80% ethanol
		dip	(v/v)
		2) Freeze-drying; air-drying;		Nutraceuticals		(Wolfe and Liu, 2003)
		oven-drying
		(40/60/80°C,
		no air
		circulation)
	Antioxidant	Freeze-	Methanol	Functional foods Phenolic	(Huber and
	peel extracts	drying			compounds	Rupasinghe, 2009)
				Functional foods Phenolic	(Wegrzyn et al.,
					compounds	2008)
			Ethanol ;	Nutraceuticals	Phenolic	(Tanabe et al.,
			methanol		compounds	1999)
		Freeze-	80% Acetone	Nutraceuticals	Phenolic	(Wolfe et al., 2003)
		drying	(v/v)		compounds

Table I .

 I 4. Polyphenols extraction methods.

	Technologies	Advantages			Disadvantages	References
	Solvent	Cell membranes more	Time-consuming, low yields and	(Bai et al., 2010;
	diffusion	vulnerable, easy operation	submit polyphenols to thermal	Guo et al., 2007)
						degradation or oxidation
	Enzyme	High selectivity		Cost of enzymes, difficult to	(Oszmiański	et
						scale-up	al., 2011; Pinelo
							et al., 2008)
	Pressurized	Lower			solvent	High implementations costs	(Grigoras et al.,
	fluid	requirement,	reduced		2013)
		costs with chemicals and
		effluent treatment, smaller
		ecological impacts
	Supercritical	Higher process efficiency	Difficult to scale-up, not	(Adil et al., 2007;
	fluid	and lesser detrimental	efficient in the extraction of	Massias et al.,
		ecological effects, lower	polar polyphenols	2015)
		operation temperatures,
		preserving the material
		composition;	reducing
		degradation reactions
	Ultrasound	Consume	less	fossil	Long time and high temperature (Corrales et al.,
		energy and permit the		2008; Pingret et
		reduction of solvents		al., 2012)
	Microwave	Reduce both extraction	Long time and a distinct	(Hemwimon	et
		time	and	solvent	temperature increase	al., 2007; Spigno
		consumption				and De Faveri,
							2009)
	Pulsed electric	Preserve the structure of	Less effective from dried raw	(Boussetta et al.,
	fields	the	product,	low	materials	2015; Grimi et al.,
		temperature increase		2010)
	High voltage	Low		temperature
	electrical	increase, short times of
	discharges	treatment and low energy
		consumption

Table I .

 I 5. The HVED-assisted extraction of polyphenols from various food materials.

	Materials	HVED	Polyphenols content	References
	Orange peels 222 kJ/kg	0.7 g/100 g DM	(El Kantar et al., 2018)
	Olive kernels 66 kJ/kg	626.6 mg/L	(Roselló-Soto et al., 2015a)
	Grape stems	188 kJ/kg	6.6 ± 0.2 g/100 g RM	(Brianceau et al., 2016)
	Blackberries 9.6 kJ/kg	932.69 ± 33.45 mg/100 g DM	(Barba et al., 2015a)
	Vine shoots	10 kJ/kg	34.5 mg/DM	(Rajha et al., 2014)
	Sesame cake 83 kJ/kg	20.3 ± 0.9 g/100 DM	(Sarkis et al., 2015)
	Grape peels	120 kJ/kg	21.4 ± 0.8 μmol/g DM	(Boussetta et al., 2009)
	Grape pomace 80 kJ/kg	2.8 ± 0.4 g/100g DM	(Boussetta et al., 2011)
	Grape seeds	26.4 kJ/kg	9 g/100 g DM	(Boussetta et al., 2012)
	Papaya seeds 22.1 kJ/kg	95 mg/L	(Parniakov et al., 2015)
	Grape seeds	24 kJ/kg	8.3 g/100 DM	(Liu et al., 2011)
	DM: dry matter, RM: raw matter
	It was demonstrated that HVED was more efficient than PEF for extraction of polyphenols
	from grape peels

  .Abid et al. (2014) proved that US (frequency 25 kHz, intensity of 2 W/cm 2 ), applied at 20 °C for 30 min enhanced effectively the TPC extraction from apple juice. The UAE for recovery of polyphenols from the unripe apple at different concentrations of ethanol (40-90% v/v), temperature (30-80 °C), extraction time (10-30 min), and ultrasound power (280-560 W) has been tested[START_REF] Yue | Ultrasound-assisted extraction, HPLC analysis, and antioxidant activity of polyphenols from unripe apple[END_REF]. At optimum extraction conditions (ethanol concentration of 50%, temperature of 50 °C, extraction time of 30 min, ultrasonic power of ≈520 W), the maximum TPC of 13.26 ± 0.56 mg GAE/g could be

obtained. Application of UAE at optimal conditions (US of 25 kHz and 150 W, 50% v/v ethanol/aqueous solvent, solid/liquid ratio of 15% w/v and moderate temperatures 16-34 °C)

Table I

 I

	ADS-5	Non	SDVB	520-600	250-300 300-1250 (Fu et al., 2007; W.
							Liu et al., 2010)
	ADS-17 moderate acrylic	250-300	90-150	300-1250 (Ma et al., 2009a)
	AL-2	Polar	SDVB	550-600	150-250 300-1250 (Fu et al., 2006)
	D101	Non	SDVB	480-550	90-150	300-1250 (Fu et al., 2005; Wan
							et al., 2008)
	DM11	Non	SDVB	≥500	70-80	315-1250 (Lv et al., 2008)
	DM-301 Weak	SDVB	≥330	140-170 300-1250 (Lv et al., 2008)
	DS-401 Weak	SDVB	≥480	120-140 300-1250 (Wan et al., 2008)
	HP-20	Non	SDVB	600	520	300-1250 (Yang et al., 2009)
	HP-100 Non	SDVB	650-700	85-90	300-1250 (Jia and Lu, 2008; Lv
							et al., 2008; Yang and
							Tan, 2008)
	HP-200 Non	SDVB	700-750	85-90	300-1250 (Ma et al., 2009a,
							2009b)
	HP-500 Polar	SDVB	500-550	100-120 300-1250 (Lv et al., 2008)
	HP-600 Polar	SDVB	500-550	100-120 300-1250 (Ma et al., 2009a)
	HP-800 moderate SDVB	700-750	90-110	300-1250 (Gao et al., 2007)
	HP-850 Polar	SDVB	1100-1300 85-95	300-1250 (B. Zhang et al.,
							2008b)
	LSA-10 moderate methacrylic 500-540	85-90	300-1250 (Fu et al., 2005; Ma et
							al., 2009b)
	LSA-20 Non	methacrylic 420-500	85-90	300-1250 (Fu et al., 2005)
	NKA11 Polar	SDBV	160-200	145-155 300-1250 (Lv et al., 2008)
	XAD-7	Weak	acrylic	450	90	250-840	(Li and Chase, 2010)
	XAD-16 Non	SDVB	630	210	250-840	(Li and Chase, 2010)
	XAD-	Non	SDVB	700	400	250-840	(Yang et al., 2009)
	1180
	XAD-	Non	SDVB	800	150	250-840	(Yang et al., 2009)
	1600 XAD-1	.6. Comparison of various macroporous resins and their physical properties Non SDVB 800-1000 85-95 300-1250 (Fu et al., 2005; Jin et
				(Li and Chase, 2010)		al., 2008)
	Resin XAD-6	Polarity Polar	Matrix SDVB	Surface 450-500	Pore (Å) 120-160 300-1250 (Ma et al., 2009b) Particle References
				area(m 2 /g)	diameter	size (μm)
	AB-8	Weak	SDVB	480-520	130-140 300-1250 (Ma et al., 2009a,
							2009b; Yang et al.,
							2009)

Table I

 I

	Polyphenol type	Molecular weight (MW)
	Catechin	290.3
	Epi-catechin	290.3
	Epi-catechin gallate	442.4
	Procyanidin dimer	578.5
	Procyanidin trimer	870
	Procyanidin tetramer	1160
	Kaempferol	286.2
	Gallic acid	170.1
	Quercetin	448.4
	Caffeic acid	180.2
	Coumaric acid	164.2
	Chlorogenic acid	354.3

.7. Molecular weight of various polyphenols

[START_REF] García | Bioseparation process science[END_REF]

Table II .

 II 1 Properties of used membranes Name of membrane Molecular weight cut-off (MWCO) Pore size, d m

	MP005	45660 kDa	50 nm
	UP150	150 kDa	10 nm
	UH030	30 kDa	4.35 nm
	UP010	10 kDa	3.02 nm
	For every filtration test, new membrane was used.

Acknowledgements

V.2 Article VI Ultrasound assisted purification of polyphenols of apple skins by adsorption/desorption procedure

Summary

First of all, adsorption/desorption procedure with ultrasound treatment on the polyaromatic amberlite adsorbent XAD-16 was carried out to evaluate the feasibility of polyphenols purification (details are presented in article VI Ultrasound assisted purification of polyphenols of apple skins by adsorption/desorption procedure). Adsorption/desorption method using resin adsorbents was beneficial for the concentration and purification of phenolic compounds due to polyphenol substances could be adsorbed on the adsorbents with the strong noncovalent bonding and aromatic stacking and subsequently could be easily desorbed into organic solvents. However, the conventional adsorption/desorption procedures are time-consuming [START_REF] Buran | Adsorption/desorption characteristics and separation of anthocyanins and polyphenols from blueberries using macroporous adsorbent resins[END_REF][START_REF] Zagklis | Purification of grape marc phenolic compounds through solvent extraction, membrane filtration and resin adsorption/desorption[END_REF]. US treatment during adsorption/desorption procedures can reduce purification time and increase purification effect by accelerating mass-transfer and adsorption efficiency. US has been applied to improve adsorption of phenolic compounds, aromatic pollutants, dyes, anthocyanins, and metal ions [START_REF] Ali | Ultrasound-assisted adsorption of phenol from aqueous solution by using spent black tea leaves[END_REF][START_REF] Breitbach | Stability of adsorber resins under mechanical compression and ultrasonication[END_REF][START_REF] Dastkhoon | Ultrasound assisted adsorption of malachite green dye onto ZnS: Cu-NP-AC: equilibrium isotherms and kinetic studies--response surface optimization[END_REF][START_REF] Ji | Effect of ultrasound on adsorption of Geniposide on polymeric resin[END_REF][START_REF] Jing | Ultrasound enhanced adsorption and desorption of chromium (VI) on activated carbon and polymeric resin[END_REF][START_REF] Juang | Liquid-phase adsorption and desorption of phenol onto activated carbons with ultrasound[END_REF][START_REF] Midathana | Mechanistic studies in ultrasound-assisted adsorption for removal of aromatic pollutants[END_REF]. Ultrasound-assisted purification of polyphenols from apple peel extracts by adsorption/desorption procedure based on using the adsorbent resins can be considered as the "green" purification technology with reduction of organic solvents and absorbents consumption, energy consumption, and purification time (Chemat et al., 2017a(Chemat et al., , 2017b)).

Therefore in this part, the adsorption steps at different temperatures (T=25-40 °C) with application of US at different intensities (P=0-400 W) were studied. In addition, the effect of ethanol concentration in aqueous ethanol solution (C e =0-96%) on desorption steps was analyzed. The isotherm of polyphenol adsorption, the adsorption kinetic curves and desorption kinetic curves were studied. The obtained data from adsorption/desorption experiment evidenced that the adsorption kinetics were fitted with stretched exponential law and evidenced that the presence of broad distribution of adsorption times that can depend on content of polyphenols in the solutions and applied power of sonication. The adsorption isotherm was fitted using the Freundlich isotherm model that also assumes the presence of adsorption on heterogeneous surface. Since the results demonstrated that the sonication significantly facilitated absorption kinetics, increased adsorption capacity and activation energy of polyphenols adsorption. The effects of US power on the damage of XAD-16 were