Gwénaëlle ; Jard

T Liboz
email: liboz@ensat.fr

F Mathieu

A Guyonvarc'

A Lebrihi

Review of mycotoxin reduction in food and feed: from prevention in fields to detoxification by adsorption or transformation

Keywords: Mycotoxins Food Types: Animal feed, Cereals mycotoxins, decontamination, adsorption, binding agents, sequestering agents, transformation, detoxification

Mycotoxins are secondary metabolites present worldwide in agricultural commodities and produced by filamentous fungi that cause a toxic response (mycotoxicosis) when ingested by animals. Prevention of mycotoxicoses includes pre-and post-harvest strategies. The best way to reduce the mycotoxin content in food and feed is the prevention of mycotoxin formation in the field but this is often not sufficient so that other methods are needed. To decontaminate and/or detoxify mycotoxin-contaminated food and feed, the most prevalent approach in the feed industry is the inclusion of sorbent materials in the feed thus obtaining more or less selective removal of toxins by adsorption during passage through the gastrointestinal tract. Another reliable approach is to add enzymes or microorganisms capable of detoxifying some mycotoxins. Through a comprehensive review of published reports on the strategies for mycotoxin removal, this present work aims to update our understanding of mycotoxin removal. It could provide insight in the detoxification in mycotoxin present in food and feed. In the future, more emphasis should be placed on adsorption of mycotoxins in the gastrointestinal tract. Concerning the enzymatic transformation of mycotoxins, further effort is required in understanding detoxification reactions, the toxicity of transformation products and in the characterization of enzymes responsible for the transformations.

Mycotoxins are secondary metabolites present worldwide in agricultural commodities and produced by filamentous fungi that cause a toxic response (mycotoxicosis) when ingested by animals. Prevention of mycotoxicoses includes pre-and post-harvest strategies. The best way to reduce the mycotoxin content in food and feed is the prevention of mycotoxin formation in the field but this is often not sufficient so that other methods are needed. To decontaminate and/or detoxify mycotoxin-contaminated food and feed, the most prevalent approach in the feed industry is the inclusion of sorbent materials in the feed thus obtainig more or less selective removal of toxins by adsorption during passage through the gastrointestinal tract. Another reliable approach is to add enzymes or microorganisms capable of detoxifying some mycotoxins. Through a comprehensive review of published reports on the strategies for mycotoxin removal, this present work aims to In the future, more emphasis should be placed on adsorption of mycotoxins in the gastrointestinal tract. Concerning the enzymatic transformation of mycotoxins, further effort is required in understanding detoxification reactions, the toxicity of transformation products and in the characterization of enzymes responsible for the transformations. ways: fungi growing either as pathogens on plants in field or on stored plants [START_REF] Glenn | Mycotoxigenic Fusarium species in animal feed[END_REF].

All moulds are not toxigenic and while some mycotoxins are produced by only a limited number of species, others may be produced by a relatively large range from several genera. Up to now, there have been reported approximately 400 secondary metabolites with toxigenic potential produced by more than 100 moulds. Examples of some well-known mycotoxins are aflatoxins, fumonisins, ochratoxin, trichothecenes, zearalenone, penitrems and ergot alkaloids. The Food and Agriculture Organization (FAO) estimates that 25% of the world's agricultural commodities are contaminated with mycotoxins, leading to significant economic losses [START_REF] Wu | Measuring the economic impacts of Fusarium toxins in animal feeds[END_REF]. Mycotoxins are small and quite stable molecules which are extremely difficult to remove or eradicate, and which enter the feed chain while keeping their toxic properties. Consumption of a mycotoxin-contaminated diet may induce acute and longterm chronic effects in animals and humans resulting in teratogenic, carcinogenic and oestrogenic or immune-suppressive effects. Data on mycotoxin levels in mycotoxin contamination causing a reduction in zootechnical performance in farm animals (ruminants, pigs and poultry) were compiled in the AFSSA report [START_REF] Afssa | Évaluation des risques liés à la présence de mycotoxines dans les chaînes alimentaires humaine et animale[END_REF]. Direct consequences of consumption of mycotoxin-contaminated animal feed include: reduced feed intake, poor feed conversion, diminished body weight gain, increased incidence of disease (due to immunesuppression) and reduced reproductive capacity [START_REF] Fink-Gremmels | Clinical effects and biochemical mechanisms associated with exposure to the mycoestrogen zearalenone[END_REF][START_REF] Morgavi | An historical overview of field disease outbreaks known or suspected to be caused by consumption of feeds contaminated with Fusarium toxins[END_REF][START_REF] Pestka | Deoxynivalenol: Toxicity, mechanisms and animal health risks[END_REF][START_REF] Voss | Fumonisins: Toxicokinetics, mechanism of action and toxicity[END_REF].

The diversity of mycotoxin structures induces diverse toxic effects. For example, the aflatoxin structure permit the formation of DNA adducts with guanine inducing cancerous cell formation [START_REF] Bren | Guanine alkylation by the potent carcinogen aflatoxin B1: quantum chemical calculations[END_REF]. The lactone ring of aflatoxins is responsible for its toxicity [START_REF] Lee | Role of lactone ring of aflatoxin B1 in toxicity and mutagenicity[END_REF]. Fumonisins could inhibit the ceramide synthase [START_REF] Soriano | Mechanism of action of sphingolipids and their metabolites in the toxicity of fumonisin B1[END_REF] inducing adverse effect on the sphinganin/sphingosin ratio. The deamination of fumonisin B1 induces a loss of toxicity indicating that amine play a role in fumonisin toxicity. Ochratoxins affect the protein synthesis and inhibit the ATP production. The toxicity of ochratoxins is associated with its isocoumarin moiety [START_REF] Xiao | Toxicity of ochratoxin A, its opened lactone form and several of its analogs: structure-activity relationships[END_REF]. Deoxynivalenol (DON) and T-2 toxin induce apoptosis in haemopoietic progenitor cells and immune cells [START_REF] Parent-Massin | Haematotoxicity of trichothecenes[END_REF]. They also inhibit protein, ADN and ARN synthesis [START_REF] Richard | Some major mycotoxins and their mycotoxicoses-an overview[END_REF]. The epoxy structure of trichotecenes induces their toxicity [START_REF] Sundstøl ; Eriksen | Comparative cytotoxicity of deoxynivalenol, nivalenol, their acetylated derivatives and de-epoxy metabolites[END_REF]. Zearalenone (ZEA) thanks to its conformation is able to mimick 17β-estradiol and to bind to estrogen receptors disrupting fertility and reproduction ability [START_REF] Gaumy | Zéaralénone : propriétés et toxicité expérimentale[END_REF].

Prevention of mycotoxicoses includes pre-and post-harvest strategies. The best way is the prevention of mycotoxin formation in the field but this is often not sufficient and other strategies are needed. To decontaminate and/or detoxify mycotoxin-contaminated food and feed, the most prevalent approach in the feed industry is the inclusion of sorbent materials in the feed to obtain more or less selective removal of toxins by adsorption during passage through the gastrointestinal tract, or to add enzymes or microorganisms capable of detoxifying certain mycotoxins. A new functional group of feed additives as "substances for Through a comprehensive review of published reports on the strategies for removing mycotoxins by both adsorption and transformation, this present work aims to update our understanding of removal of mycotoxins and it could provide insight in the elimination and detoxification in mycotoxin present in food and feed. Numerous recent reports have been previously published on part of this field [START_REF] Kabak | Strategies to prevent mycotoxin contamination of food and animal feed: A review[END_REF][START_REF] Schatzmayr | Microbiologicals for deactivating mycotoxins[END_REF][START_REF] Jouany | Methods for preventing, decontaminating and minimizing the toxicity of mycotoxins in feeds[END_REF]EFSA, 2009;[START_REF] Awad | Decontamination and detoxification strategies for the Fusarium mycotoxin deoxynivalenol in animal feed and the effectiveness of microbial biodegradation[END_REF][START_REF] He | Chemical and biological transformations for detoxification of trichothecene mycotoxins in human and animal food chains: a review[END_REF] but none of them propose an overview on mycotoxin elimination from prevention in fields to mycotoxin detoxification.

Preventive strategies: controlling mould development

Moulds can develop on plants or plant products during cultivation or storage.

Depending on environmental conditions, some of these moulds may produce mycotoxins leading to harmful consequences for consumers. So, primary strategy should aim to eliminate mycotoxins reducing mould proliferation during cultivation and storage. [START_REF] Magan | Post-harvest control strategies: Minimizing mycotoxins in the food chain[END_REF] synthesized interesting studies on this topic. In the following discussion, we will mention a number of strategies which could be used.

Planting

Crop varieties selection

Seeds must be free of pests and disease before planting, to ensure healthy, vigorous plants capable of withstanding attack during the growing season. A possible strategy is also to select crop varieties on their ability to resist mould attack [START_REF] Clements | Identifying sources of resistance to aflatoxin and fumonisin contamination in corn grain[END_REF].

Sowing date

Sowing date is another element of crop management that has an indirect effect on the production and infection by spores because it partly determines the flowering date, together with the variety sown and prevailing weather. If the sowing date is such that flowering coincides with spore release, then more frequent and severer attacks are likely [START_REF] Champeil | Influence of cropping system on Fusarium head blight and mycotoxin levels in winter wheat[END_REF]. As far as practical, crop planting should be timed to avoid high temperature and drought stress during the period of seed development and maturation (Codex alimentarius, 2003). In the first place, using suitable cultivation techniques can reduce the risk of fungal contamination. For example, removal of agricultural waste is effective in preventing the contamination of the follow-on crops. Indeed, the primary reservoir of fungal inoculum is the residues from previous crops. Also, ploughing limits mould contamination [START_REF] Munkvold | Cultural and genetic approaches to managing mycotoxins in maize[END_REF][START_REF] Champeil | Influence of cropping system on Fusarium head blight and mycotoxin levels in winter wheat[END_REF]. The effects of crop rotation are also significant. For example, wheat following maize in the rotation has been found to have DON concentrations six times higher than those in wheat following another cereal (wheat, barley) or soybean [START_REF] Krebs | Effect of tillage and Preceding crops on Fusarium infection and deoxynivalenol content of wheat[END_REF].

Pre-harvest

Suitable cultivation techniques

In that context, Codex alimentarius (2003) established some good agricultural practices for farmers for the prevention and reduction of mycotoxin contamination in cereals. For example, it is suggested to use crops such as potato, other vegetables, clover and alfalfa that are not hosts to Fusarium species in rotation to reduce the inoculum in the field. Drought stress, caused by a lack of water, is known to facilitate attack by mould. Lack of water allows the plant to crack, and so opens passage ways through which fungal spores can enter.

Predictive models

Softwares applications are available to help farmers predict mycotoxin risk during the year as a function of climatic parameters [START_REF] Schaafsma | Climatic models to predict occurrence of Fusarium toxins in wheat and maize[END_REF][START_REF] Prandini | Review of predictive models for Fusarium head blight and related mycotoxin contamination in wheat[END_REF].

Fungicides could be useful whenever a predictable risk exists [START_REF] Paul | Efficacy of Triazole-Based Fungicides for Fusarium Head Blight and Deoxynivalenol Control in Wheat: A Multivariate Meta-Analysis[END_REF]. However, risk management must take into account other risks for consumer health linked to the presence of fungicides in food. In this context, a recent study compared the toxicity of two fungicides and two mycotoxins, ZEA and DON [START_REF] Muri | Comparison of human health risks resulting from exposure to fungicides and mycotoxins via food[END_REF]. The final results showed that DON was more toxic than both ZEA and the two tested fungicides. However, other studies have shown that conventional agriculture using fungicides induces higher risks than organic farming [START_REF] Finamore | Novel approach for food safety evaluation. Results of a pilot experiment to evaluate organic and conventional foods[END_REF][START_REF] Schneweis | Influence of organically or conventionally produced wheat on health, performance and mycotoxin residues in tissues and bile of growing pigs[END_REF]. For example, maize from an organic farm had a 50% lower Fusarium infection rate than maize from a conventional farm probably due in large part to the lower intensity of cultivation, different crop rotation, ploughing and the heightened biomass activity of organic soils [START_REF] Arino | Natural occurrence of Fusarium species, fumonisin production by toxigenic strains, and concentrations of fumonisins B[1] and B[] in conventional and organic maize grown in Spain[END_REF].

Avoiding insect attack

It is known that incidence of infection from A. flavus and A. parasiticus in damaged kernels is significantly high in comparison with healthy ones. Insects can act as fungal spore vectors or to create critical points in the commodity mass favouring fungal growth and toxin production [START_REF] Sinha | Insect pests, Aspergillus flavus and aflatoxin contamination in stored wheat: a survey at north Bihar (India)[END_REF]. Furthermore, they attack kernel external teguments and facilitate entry and colonization of mycotoxin-producing fungi. Therefore, treatments with insecticides are advisable to reduce these attacks.

Biocontrol techniques

In the fight against fusariotoxicosis, biocontrol techniques based on microorganisms are also under study to fight against [START_REF] Schisler | Greenhouse and Field Evaluation of Biological Control of Fusarium Head Blight on Durum Wheat[END_REF]. Different microorganisms have been proposed as bio-control agents of A. flavus and aflatoxins contamination in pre-harvest; nonaflatoxigenic isolated strains of the same species could be optimal bio-competitive agents.

For example, [START_REF] Dorner | Effect of application of nontoxigenic strains of Aspergillus flavus and A. parasiticus on subsequent aflatoxin contamination of peanuts in storage[END_REF] showed that treatment of soil with nontoxigenic strains of A. flavus and A. parasiticus significantly reduces preharvest aflatoxin contamination. In addition, soil treatment with nontoxigenic strains had the beneficial carry-over effect of reducing aflatoxin contamination that occurred during storage.

Post-harvest

Storage

This step is critical in preventing mold growth and mycotoxin production in harvested feedstuffs. Various important factors should be managed to prevent crops from fungal contamination during storage [START_REF] Schrödter | Influence of harvest and storage conditions on trichothecenes levels in various cereals[END_REF]. For example, grain should be stored with less than 15% moisture content to eliminate pockets with higher moisture [START_REF] Kabak | Strategies to prevent mycotoxin contamination of food and animal feed: A review[END_REF] at low temperature (Burges and Burrel, 1964). A low oxygen concentration (<1%) and an augmentation of carbon dioxide concentration are efficient to prevent mould development [START_REF] Driehuis | The impact of the quality of silage on animal health and food safety: a review[END_REF]. Physical integrity of grains should be preserved. Mixing grains and a long-time storage should be avoided.

Despite all precautions, it may happen that stored grain will become damaged by mould. It must then be assumed that the grain could also be contaminated with mycotoxins.

If the farmer has plenty of grain in store, he can afford to lose a small quantity that has turned mouldy. Ideally, the farmer must discard mouldy grain and any that is suspected of being contaminated with mycotoxins; this will include apparently clean grain that is in the vicinity of the mouldy produce. This grain should be burnt or buried.

Sorting

Contaminated grain does not have the same color or density as safe grain. Thus, grain can be sorted according to appearance or density [START_REF] Murphy | Fumonisins B1, B2, and B3 content of Iowa, Wisconsin, and Illinois corn and corn screenings[END_REF][START_REF] Guerre | Interest of the treatments of raw materials and usage of adsorbents to decontaminate animal food containing mycotoxins[END_REF][START_REF] Afolabi | Effect of sorting on incidence and occurrence of fumonisins and Fusarium verticillioides on maize from Nigeria[END_REF][START_REF] Kabak | Strategies to prevent mycotoxin contamination of food and animal feed: A review[END_REF]. These methods are not very specific and in general not exhaustive. When mycotoxin contamination is heterogeneous, the removal of the contaminated part could reduce the level of mycotoxin in the final product (Benett et al., 1978;[START_REF] Osborne | The effects of milling and processing on wheat contaminated with ochratoxin A[END_REF]. For example, apple dissection before making apple juice led to a 95% reduction of patulin [START_REF] Lovett | Trimming as a means of removing patulin from fungus-rotted apples[END_REF]. Washing of food or grain can also reduce mycotoxin levels. For example, the first step in spaghetti production with wheat is a washing which remove of 23% of DON [START_REF] Visconti | Reduction of deoxynivalenol during durum wheat processing and spaghetti cooking[END_REF]. Eliminating mycotoxins from food and feed Different methods must be used to decontaminate food and feed before ingestion. For the moment, regulations do not permit the decontamination of food that exceeds the limit concentration thresholds. Mycotoxin reduction could be carried out during food industry processes [START_REF] Bullerman | Stability of mycotoxins during food processing[END_REF] or by using additives which eliminate or deactivate mycotoxins in the organism. In all cases, decontamination processes should destroy or inactivate mycotoxins, generate no toxic products, guaranty the nutritional value of the food and induce no modification to the technological properties of the product.

Decreasing bioavailibility of mycotoxins by adsorption

Principle

Since all mycotoxins are very stable substances, no physical or chemical treatment can be applied without altering the nutritional value of the grain or causing a high rise in costs. For example, ammonia or strong oxidizing agents can reduce the contamination but will also reduce at the same time the nutritional value of the feed.

The most commonly-used technique for reducing exposure to mycotoxins is to decrease their bio-availability by the inclusion of various mycotoxin binding agents or adsorbents, which leads to a diminishing of mycotoxin uptake and subsequent distribution to the blood and target organs. These adsorbants are efficient only if the complex is stable in an animal digestive tract so that bound mycotoxins are channelled to its urine and feces.

An important criterion for the evaluation of mycotoxin adsorbants is their effectiveness at different levels of pH (acidic and neutral) since the adsorbant must be efficient throughout the entire gastro-intestinal tract and that the complex mycotoxin-adsorbant remains stable, in order to prevent desorption of the toxin during the digestion.

The properties of both adsorbant and mycotoxin play an important role in adsorbant efficacy. Indeed, the physical structure of an adsorbant, including such features as total charge and distribution, pore size and surface accessibility, must be studied. The characteristics of mycotoxins such as polarity, solubility, molecular size, shape and, in the case of ionised compounds, charge distribution and dissociation constants, are also very important.

Binders have been evaluated using both in vitro and in vivo systems. In vivo studies have generally used performance responses or biological markers such as tissue residues or changes in biochemical parameters to determine the effectiveness of binders. Numerous binders are efficient to bind aflatoxin but few of them could be used for other mycotoxins (EFSA, 2009). Thanks to its porosity, activated charcoal can adsorb the main mycotoxins in an aqueous environment. In one of the first studies to test the concept of mycotoxin binding, activated charcoal was shown to efficiently adsorb AFB1 [START_REF] Decker | Activated charcoal adsorbs aflatoxin B1[END_REF]. In subsequent studies, the effects of activated charcoal have been variable. [START_REF] Galvano | Occurrence and stability of aflatoxin M(1) in milk and milk products: A worldwide review[END_REF] showed reduced aflatoxin residues in milk of cows consuming different sources of charcoal, but responses to charcoal did not exceed that seen with a clay-based binder, a hydrated sodium calcium aluminosilicate or HSCAS [START_REF] Diaz | Aflatoxin Binders II: Reduction of aflatoxin M1 in milk by sequestering agents of cows consuming aflatoxin in feed[END_REF]. Responses to charcoal suggest that charcoal may not be as effective in binding aflatoxin as clay-based binders [START_REF] Edrington | Hydrated sodium calcium aluminosilicate (HSCAS), acidic HSCAS, and activated charcoal reduce urinary excretion of aflatoxin M1 in turkey poults. Lack of effect by activated charcoal on aflatoxicosis[END_REF][START_REF] Edrington | Influence of superactivated charcoal on the toxic effects of aflatoxin or T-2 toxin in growing broilers[END_REF]. Activated charcoal may be interesting in binding ZEA and/or DON (Döll et al., 2004;[START_REF] Bueno | In vitro binding of zearalenone to different adsorbents[END_REF][START_REF] Sabater-Vilar | In vitro assessment of adsorbents aiming to prevent deoxynivalenol and zearalenone mycotoxicoses[END_REF]. In an in vitro gastrointestinal model, activated carbon reduced availability of ZEA, DON andnivalenol (Avantaggiatto et al., 2003, 2004). However, adsorption of ochratoxin A (OTA) does not lead to a positive effect on chicken body weight [START_REF] Rotter | Influence of dietary charcoal on ochratoxin A toxicity in Leghorn chicks[END_REF]. On FB1, the ratio sphinganine/shingosine was not modified in rats after charcoal was added to contaminated feed [START_REF] Solfrizzo | In vitro and in vivo studies to assess the effectiveness of cholestyramine as a binding agent for fumonisins[END_REF]. For T-2 and HT-2 toxins, responses have been variable depending on the animals. For example, a 50% survival rate for mice fed with contaminated feed was observed while a 90% survival rate was reached after the addition of charcoal [START_REF] Fricke | Assessment of efficacy of activated charcoal for treatment of acute T-2 toxin poisoning[END_REF]. On the other hand, there was no effect on chicken: a decrease in 20% of body weight was observed with or without treatment.

Silicate binders. Silicates are divided into subclasses according to their structure. One such group is the phyllosilicate family, characterised by a sheet-type framework. Perhaps the most extensively studied of these materials is termed hydrated sodium calcium aluminosilicates (HSCASs). Several reviews are available [START_REF] Ramos | Intestinal absorption of zearalenone and in vitro study of non-nutritive sorbent materials[END_REF]Döll and Dänicke, 2004;[START_REF] Avantaggiato | Recent advances on the use of adsorbent materials for detoxification of Fusarium mycotoxins[END_REF]. 80% of AFB1 could be adsorbed by HSCASs in vitro [START_REF] Phillips | Hydrated sodium calcium aluminosilicate: A high affinity sorbent for aflatoxin[END_REF]) and could prevent aflatoxicosis. Positive effects of other HSCASs on drosophile progeny [START_REF] Sisman | The protective effect of hydrated sodium calcium aluminosilicate against the adverse effects of Aflatoxin B-1 on D. melanogaster[END_REF] were also observed. Furthermore, responses to HSCASs appear to be dose dependent [START_REF] Smith | Hydrated sodium calcium aluminosilicate reduction of AFM1 residues in dairy goat milk[END_REF]. HSCASs are thought to absorb aflatoxin selectively during the digestive process, which renders much of the aflatoxin unavailable for absorption from the gastrointestinal tract [START_REF] Kubena | Efficacy of a hydrated sodium calcium aluminosilicate to reduce the toxicity of aflatoxin and T-2 toxin[END_REF]. The chemisorption of aflatoxin to HSCAS involves the formation of a complex by the β-keto-lactone or bilactone system of aflatoxin with uncoordinated metal ions in HSCAS [START_REF] Sarr | Effects of molecular structure on the chemisorption of aflatoxin B1 and related compounds by hydrated sodium calcium aluminosilicate[END_REF]. AFB1 may react at surfaces and within the interlayers of HSCAS particles [START_REF] Phillips | Selective chemisorption and detoxification of aflatoxins by phyllosilicate clay[END_REF][START_REF] Phillips | Characterization of clay-based enterosorbents for the prevention of aflatoxicosis[END_REF][START_REF] Phillips | Reducing human exposure to aflatoxin through the use of clay: a review[END_REF]. Some sorbents such as NovaSil clay act as selective enterosorbents since they do not affect the serum concentrations of important vitamins and nutrient minerals in humans [START_REF] Afriyie-Gyawu | NovaSil clay does not affect the concentrations of vitamins A and E and nutrient minerals in serum samples from Ghanaians at high risk for aflatoxicosis[END_REF]. In general, HSCAS have low affinity with OTA [START_REF] Huff | Efficacy of Hydrated Sodium Calcium Aluminosilicate to Reduce the Individual and Combined Toxicity of Aflatoxin and Ochratoxin-A[END_REF][START_REF] Galvano | Activated carbons: In vitro affinity for ochratoxin A and deoxynivalenol and relation of adsorption ability to physicochemical parameters[END_REF].

Adsorption results for ZEA are variable: some studies show a decrease in chromosomic aberrations for mice [START_REF] Abbes | Preventive role of aluminosilicate clay against induction of micronuclei and chromosome aberrations in bone-marrow cells of Balb/c mice treated with Zearalenone[END_REF] and a positive effect on the length of mink gestation [START_REF] Bursian | Efficacy of hydrated sodium calcium aluminosilicate in reducing the toxicity of dietary zearalenone to mink[END_REF]. [START_REF] Patterson | Efficacy of Hydrated Sodium-Calcium Aluminosilicate, Screening and Dilution in Reducing the Effects of Mold Contaminated Corn in Pigs[END_REF], however, failed to see any benefit in the addition of HSCAS to pig diets containing DON. This result was confirmed in vitro by [START_REF] Galvano | Activated carbons: In vitro affinity for ochratoxin A and deoxynivalenol and relation of adsorption ability to physicochemical parameters[END_REF] and [START_REF] Sabater-Vilar | In vitro assessment of adsorbents aiming to prevent deoxynivalenol and zearalenone mycotoxicoses[END_REF]. [START_REF] Garcia | Evaluation of two mycotoxin binders to reduce toxicity of broiler diets containing ochratoxin A and T-2 toxin contaminated grain[END_REF], using a silicate material, demonstrated reduced T-2 toxicity while [START_REF] Kubena | Efficacy of a hydrated sodium calcium aluminosilicate to reduce the toxicity of aflatoxin and T-2 toxin[END_REF] did not see any effect from the addition of HSCAS. [START_REF] Aly | Application of adsorbent agents technology in the removal of aflatoxin B-1 and fumonisin B-1 from malt extract[END_REF] showed an adsorption efficiency fir a mix of AFB1 and FB1 of, respectively, 95% and 85%. However, [START_REF] Watts | Effects of multiple mycotoxins and a hydrated sodium calcium aluminosilicate in poultry[END_REF] showed that 1% HSCAS did not protect chicks and poults receiving diets containing 1 mg DON, 5 mg moniliformin, 5 mg FB1, 100 µg AFB1, 1 mg ZEA and 0.5 mg OTA per kg of diet.

Other silicates that have been studied include bentonites, zeolites, clinoptilolites and various others that often have not been completely characterized. Bentonite is a general clay material originating from volcanic ash and containing primarily montmorillonite as the main constituent. Montmorillonite clay is a hydrated sodium calcium aluminum magnesium silicate hydroxide. Clays are silica sheets that are similar to other phyllosilicates but contain a high concentration of water. The zeolite structure provides vacant spaces that form channels of various sizes allowing movement of molecules into and out of the structure. Thanks to this structure, zeolithes present a very big specific surface (about 1000 m² per gramme of zeolithe).

Bentonite and montmorillonite could adsorb from 40% to 100% of OTA in wine [START_REF] Kurtbay | Reduction of ochratoxin a levels in red wine by bentonite, modified bentonites, and chitosan[END_REF]. However, Lemke et al. (2001a) failed to show a positive in vivo effect on rats. Indeed, rat uterus weight increased with montmorillonite treatments suggesting an increase of oestrogenic toxicity with treatment. A slight positive effect was observed by Carson and Smith (1983a) for the addition of bentonite in T-2 toxin-contaminated food since 8% of body weight was recovered after treatment. A 9% body weight gain was observed for chicken treated with bentonite when their feed contained a mix of AFB1 and FB1 [START_REF] Miazzo | Efficacy of sodium bentonite as a detoxifier of broiler feed contaminated with aflatoxin and fumonisin[END_REF]. Another study performed by [START_REF] Kubena | Effects of a hydrated sodium calcium aluminosilicate (T-Bind) on mycotoxicosis in young broiler chickens[END_REF] demonstrated that an HSCAS could provide protection against AFB1 but not against T-2 toxin in young broiler chicks.

Zeolites are very efficient in bovine rumen juice since 100% of AFB1 was adsorbed [START_REF] Spotti | Aflatoxin B1 binding to sorbents in bovine ruminal fluid[END_REF]. Zeolites have not proven to reduce the toxicity of T-2 toxin [START_REF] Dvorska | Effects of T-2 toxin, zeolite and Mycosorb on antioxidant systems of growing quail[END_REF]. However, some types of clinoptilotite could not be used as a binder since its adding in presence of AFB1 caused severe lesions. This could be explained by a nonspecific adsorption of important compounds involved in aflatoxicosis regulation [START_REF] Mayura | Prevention of maternal and developmental toxicity in rats via dietary inclusion of common aflatoxin sorbents: potential for hidden risks[END_REF].

A number of studies have examined chemically-modified silicates. Döll et al. (2004) examined a chemically-modified aluminosilicate that showed good binding with ZEA in vitro, confirming previous work [START_REF] Lemke | Adsorption of zearalenone by organophilic montmorillonite clay[END_REF][START_REF] Tomasevic-Canovic | Surfactant modified zeolite-new efficient adsorbents for mycotoxins[END_REF]. Others have shown that chemical modifications have increased the binding of HSCAS with ZEA [START_REF] Pimpukdee | The characterization of clays and cetylpyridinium-exchanged clays for their ability to adsorb zearalenone[END_REF]. Non-modified zeolithes are used to adsorb AFB1 while hydrophobic zeolithes (octadecyldimethylbenzyl, an ammonium-treated zeolite) are mostly used to adsorb OTA and ZEA [START_REF] Dakovic | Adsorption of ochratoxin A on octadecyldimethyl benzyl ammonium exchanged-clinoptilolite-heulandite tuff[END_REF][START_REF] Dakovic | Adsorption of mycotoxins by organozeolites[END_REF][START_REF] Dakovic | Adsorption of zearalenone by organomodified natural zeolitic tuff[END_REF]. The adsorption efficiency of hydrophobic zeolithes could be explained by hydrophobic interactions between OTA and ZEA and the binder.

Other mineral adsorbants. Some synthetic polymers such as cholestryamine and polyvinylpyrrolidone can adsorb mycotoxins. Undigestible dietary fiber has adsorbance potential for mycotoxins. Fibers have reduced the effects of ZEA [START_REF] Tangni | Biological method for detoxification of a liquid food medium[END_REF] in rats and swine and T-2 toxin in rats (Carson and Smith, 1983b). Cholestyramine resin is used in human medicine for the reduction of cholesterol and functions through adsorption of bile acids. Cholestyramine has been shown to adsorb ZEA [START_REF] Ramos | Intestinal absorption of zearalenone and in vitro study of non-nutritive sorbent materials[END_REF]Döll et al., 2004;[START_REF] Avantaggiato | Recent advances on the use of adsorbent materials for detoxification of Fusarium mycotoxins[END_REF] and FB1 [START_REF] Solfrizzo | In vitro and in vivo studies to assess the effectiveness of cholestyramine as a binding agent for fumonisins[END_REF]. In rats consuming OTA, cholestyramine increased fecal OTA excretion [START_REF] Kerkadi | Dietary cholestyramine reduces ochratoxin A-induced nephrotoxicity in the rat by decreasing plasma levels and enhancing fecal excretion of the toxin[END_REF]. In another in vivo study, cholestyramine did not bind OTA [START_REF] Bauer | Moglichkeiten zur Entgiftung mykotoxinhaltiger Futtermittel[END_REF]. Only 5% of DON could be adsorbed by cholestyramine in a dynamic digestive tract [START_REF] Avantaggiato | Recent advances on the use of adsorbent materials for detoxification of Fusarium mycotoxins[END_REF].

A synthetic water-soluble polymer, polyvinlypyrrolidone (PVP), has been investigated as a binder for mycotoxins. PVP is reported to bind with AFB1 and ZEA in vitro [START_REF] Alegakis | Deactivation of mycotoxins. I. An in vitro study of zearalenone adsorption on new polymeric adsorbents[END_REF] but did not alleviate the toxicity of DON seen in pigs [START_REF] Friend | Effects of adding potential vomitoxin (deoxynivalenol) detoxicants or a F. graminearum inoculated corn supplement to wheat diets to pigs[END_REF]. Some commercial adsorbants consist of a mixture of different adsorbants. For example, the product Standard Q/FIS allies charcoal and HSCAS. These products are in general tested for their capacity to adsorb various mycotoxins at the same time [START_REF] Avantaggiato | Assessment of the multi-mycotoxin-binding efficacy of a carbon/aluminosilicate-based product in an in vitro gastrointestinal model[END_REF].

Limits of mineral adsorbants. Mineral adsorbants are in general efficacious against AFB1 but their efficacy varies for other mycotoxins. Moreover, in some cases, the addition of clay increases the effects of mycotoxicosis (Carson and Smith, 1983a;[START_REF] Mayura | Prevention of maternal and developmental toxicity in rats via dietary inclusion of common aflatoxin sorbents: potential for hidden risks[END_REF]Lemke et al., 2001a). Furthermore, these adsorbants are not specific to mycotoxins and could adsorb other types of molecules, some of which essential for fighting mycotoxicosis or in nutrition [START_REF] Mayura | Prevention of maternal and developmental toxicity in rats via dietary inclusion of common aflatoxin sorbents: potential for hidden risks[END_REF].

Organic adsorbants. Humic acids are complex organic substances, a component of humus.

They also have the capacity to adsorb mycotoxins, especially AFB1 and ZEA (Jansen van [START_REF] Jansen Van Rensburg | In vitro and in vivo assessment of humic acid as an aflatoxin binder in broiler chickens[END_REF] but not DON [START_REF] Sabater-Vilar | In vitro assessment of adsorbents aiming to prevent deoxynivalenol and zearalenone mycotoxicoses[END_REF].

Biological adsorbants

Because of the limitations of mineral adsorption, many studies have been conducted over the last decade on biological adsorbents, trying to obtain greater efficacy and specificity Yeast or yeast extract. One example is Saccharomyces cerevisiae which has been shown to bind with AFB1 [START_REF] Shetty | Saccharomyces cerevisiae and lactic acid bacteria as potential mycotoxin decontaminating agents[END_REF] and reduce the detrimental effects of AFB1 in broiler diets [START_REF] Stanley | The use of Saccharomyces cerevisiae to suppress the effects of aflatoxicosis in broiler chicks[END_REF] or on rats [START_REF] Madrigal-Santillán | Antigenotoxic effect of Saccharomyces cerevisiae on the damage produced in mice fed with aflatoxin B1 contaminated corn[END_REF]. The protective effect of live yeast against aflatoxin was confirmed in rats but thermolysed yeast was shown to be ineffective [START_REF] Babtista | Thermolysed and active yeast to reduce the toxicity of aflatoxin[END_REF]. In contrast, some thermolysed yeast cell walls were more efficient in adsorbing ZEA [START_REF] Yiannikouris | Etude des mécanismes chimiques impliqués dans la complexation de mycotoxines par les composants de la paroi cellulaire de la levure Saccharomyces cerevisiae[END_REF]. Esterified glucomannan polymer extracted from the yeast cell wall was shown to bind with AFB1, OTA [START_REF] Bejaoui | Ochratoxin A removal in synthetic and natural grape juices by selected oenological Saccharomyces strains[END_REF][START_REF] Cecchini | Influence of yeast strain on ochratoxin A content during fermentation of white and red must[END_REF][START_REF] Angioni | In vitro interaction between ochratoxin A and different strains of Saracchomyces cerevisiae and Kloeckera apiculata[END_REF] and T-2 toxin [START_REF] Freimund | Efficient adsorption of the mycotoxins zearalenone and T-2 toxin on a modified yeast glucan[END_REF], individually and in combination [START_REF] Raju | Influence of esterified-glucomannan on performance and organ morphology, serum biochemistry and haematology in broilers exposed to individual and combined mycotoxicosis (aflatoxin, ochratoxin and T-2 toxin)[END_REF][START_REF] Yiannikouris | Etude des mécanismes chimiques impliqués dans la complexation de mycotoxines par les composants de la paroi cellulaire de la levure Saccharomyces cerevisiae[END_REF][START_REF] Aravind | Efficacy of esterified glucomannan to counteract mycotoxicosis in naturally contaminated feed on performance and serum biochemical and hematological parameters in broilers[END_REF][START_REF] Karaman | Evaluation of the detoxifying effect of yeast glucomannan on aflatoxicosis in broilers as assessed by gross examination and histopathology[END_REF]. Additions of esterified glucomannan at 0.5 or 1.0 g/kg to diets containig 2 mg of total aflatoxin resulted in dose-dependent responses in broiler chicks [START_REF] Basmacioglu | Effect of dietary esterified glucomannan on performance,serum biochemistry and haematology in broilers exposed to aflatoxin[END_REF]. The addition of esterified glucan polymer to aflatoxincontaminated diets of dairy cows has significantly reduced milk aflatoxin residues [START_REF] Diaz | Aflatoxin Binders II: Reduction of aflatoxin M1 in milk by sequestering agents of cows consuming aflatoxin in feed[END_REF]. The body weight and biochemical parameters were recovered in horses after adding glucomannan to their diet [START_REF] Raymond | Effects of feeding a blend of grains naturally contaminated with Fusarium mycotoxins on feed intake, serum chemistry, and hematology of horses, and the efficacy of a polymeric glucomannan mycotoxin adsorbent[END_REF]. [START_REF] Yiannikouris | Comprehensive conformational study of key interactions involved in zearalenone complexation with beta-D-glucans[END_REF] demonstrated the mechanism of binding yeast-modified glucan with ZEA. A glucan polymer bound both T-2 toxin and ZEA in vitro [START_REF] Freimund | Efficient adsorption of the mycotoxins zearalenone and T-2 toxin on a modified yeast glucan[END_REF]. The glucan polymer product gave protective against depression in antioxidant activities resulting from T-2 toxin consumed by growing quail [START_REF] Dvorska | Effects of T-2 toxin, zeolite and Mycosorb on antioxidant systems of growing quail[END_REF]. A glucan polymer product has protected swine, broilers (Swamy et al., 2002a, b) and hens [START_REF] Chowdhury | Effects of feeding blends of grains naturally contaminated with Fusarium mycotoxins on performance and metabolism of laying hens[END_REF] against some of the detrimental effects of multiple mycotoxins, but without restoring growth rate. [START_REF] Aravind | Efficacy of esterified glucomannan to counteract mycotoxicosis in naturally contaminated feed on performance and serum biochemical and hematological parameters in broilers[END_REF], using dietary additions of 0.5% esterified glucomannan, alleviated growth depression in broilers associated with naturallycontaminated diets containing AFB1, OTA, ZEA and T-2 toxin. A glucan polymer product did not alleviate the toxic effects on mink consuming diets contaminated with FB1, OTA, moniliformin and ZEA [START_REF] Bursian | Efficacy of a commercial mycotoxin binder in alleviating effects of ochratoxin A, fumonisin B-1, moniliformin and zearalenone in adult mink[END_REF]. The negative effects of ZEA and DON as measured by biochemical and immunological parameters in pig were alleviated by adding yeast extract enriched in glucomannan to their diet (Swamy et al., 2002a). 183 mg of T-2/HT-2 toxin was adsorbed per gramme of yeast-modified glucan in vitro [START_REF] Freimund | Efficient adsorption of the mycotoxins zearalenone and T-2 toxin on a modified yeast glucan[END_REF].

FB1 adsorption by yeast or yeast extract is limited [START_REF] Yiannikouris | Etude des mécanismes chimiques impliqués dans la complexation de mycotoxines par les composants de la paroi cellulaire de la levure Saccharomyces cerevisiae[END_REF]. T-2 and HT-2 binding responses are variables on yeast-modified glucan [START_REF] Freimund | Efficient adsorption of the mycotoxins zearalenone and T-2 toxin on a modified yeast glucan[END_REF].

Lactic acid bacteria. The parietal structures of some lactic acid bacteria, propionibacteria and bifidobacteria have the capacity to bind mycotoxins [START_REF] El-Nezami | Ability of Lactobacillus and Propionibacterium strains to remove aflatoxin B, from the chicken duodenum[END_REF], 2002a;[START_REF] Haskard | Surface binding of aflatoxin B(1) by lactic acid bacteria[END_REF][START_REF] Oatley | Binding of aflatoxin B-1 to bifidobacteria in vitro[END_REF]. The binding appears to be physical with DON, diacetoxyscerpenol, nivalenol, and other mycotoxins associated with hydrophobic pockets on the bacterial surface [START_REF] Haskard | Factors affecting the sequestration of aflatoxin by Lactobacillus rhamnosus strain GG[END_REF][START_REF] El-Nezami | Chemical moieties and interactions involved in the binding of zearalenone to the surface of Lactobacillus rhamnosus strains GG[END_REF]. Adsorption efficiency depends on strains [START_REF] Peltonen | Aflatoxin B1 binding by dairy strains of lactic acid bacteria and bifidobacteria[END_REF]. Adsorption of AFB1 and AFM1 was reversible and could be performed with living or dead bacteria. Acid or heat inactivation of lactic acid bacteria increased adsorption efficiency [START_REF] Haskard | Surface binding of aflatoxin B(1) by lactic acid bacteria[END_REF][START_REF] Pierides | Ability of dairy strains of lactic acid bacteria to bind aflatoxin M1 in a food model[END_REF][START_REF] El-Nezami | Physicochemical alterations enhance the ability of dairy strains of lactic acid bacteria to remove aflatoxin from contaminated media[END_REF][START_REF] Guerre | Interest of the treatments of raw materials and usage of adsorbents to decontaminate animal food containing mycotoxins[END_REF], 2002b;[START_REF] Bueno | Physical adsorption of aflatoxin B1 by lactic acid bacteria and Saccharomyces cerevisiae : a theoritical model[END_REF][START_REF] Fazeli | Aflatoxin B1 binding capacity of autochthonous strains of lactic acid bacteria[END_REF]. OTA could also be adsorbed by lactic acid bacteria [START_REF] Fuchs | Structural characterization of metabolites after the microbial degradation of type A trichothecenes by the bacterial strain BBSH 797[END_REF] and led to a diminution of toxicity on human hepatic cells [START_REF] Del Prete | In vitro removal of ochratoxin A by wine lactic acid bacteria[END_REF]. ZEA could be adsorbed between pH 4 and pH 8 (El-Nezami et al., 2002b) and heat or acid inactivation increased adsorption efficiency [START_REF] Niderkorn | Binding of Fusarium mycotoxins by fermentative bacteria in vitro[END_REF][START_REF] El-Nezami | Physicochemical alterations enhance the ability of dairy strains of lactic acid bacteria to remove aflatoxin from contaminated media[END_REF], 2002b). Binding on FB1 and DON by L.rhamnosus was not a very efficient solution [START_REF] Niderkorn | Binding of Fusarium mycotoxins by fermentative bacteria in vitro[END_REF]. Hydrophobic interactions were suspected to be involved in the binding [START_REF] Haskard | Surface binding of aflatoxin B(1) by lactic acid bacteria[END_REF].

Other biological materials. Fungal conidia are able to bind mycotoxins and especially ZEA and OTA, separatly or together [START_REF] Jard | Adsorption of zearalenone by Aspergillus japonicus conidia: new trends for biological ZON decontamination in animal feed[END_REF]. From 29% to 60% of ZEA were eliminated depending on the isolate and incubation time. [START_REF] Jard | Adsorption of zearalenone by Aspergillus japonicus conidia: new trends for biological ZON decontamination in animal feed[END_REF] suggested a hydrophobic interaction based on conidia wall characteristics. It has been suggested that conidia could be used to decontaminate wine affected by OTA [START_REF] Bejaoui | Conidia of black Aspergilli as new biological adsorbents for ochratoxin A in grape juices and musts[END_REF].

Binder efficiency

Many solutions are available for binding mycotoxins but few of them are actually used in an industrial context. Decreasing the bioavailability of AFB1 by the inclusion of binding agents is particularly effective as this group of toxins has a chemical structure which favors adsorption, especially by materials of mineral origin such as clay and zeolites. OTA, ZEA and FB1 adsorption has been more extensively studied with biological adsorbents on account of the lack of efficacy of mineral adsorbents. DON and T-2 or HT-2 toxin do not bind easily on every kind of binding agents.

A binder must be effective at sequestering the particular mycotoxin(s) targetted. In some cases, it may be of interest to bind one specific mycotoxin whereas in others, binding multiple mycotoxins may be the objective. A binder should significantly prevent toxicity in animals. There should be no serious side effects on an animal or at least, detrimental effects should not outweigh the benefits. Costs should render its use practical and profitable.

Mycotoxins residues from animals or products should not increase. Nor should there be any detrimental effects on the animal food product. Mycotoxins in feed should not be masked such that feed contamination cannot be verified. The binder should be physically usable in a commercial feed manufacturing context. Binder use and efficacy should be verifiable.

Interaction between an adsorbent and mycotoxins must produce a very strong bond in order that washing or interaction with nutrients in the digestive tract does not desorb bound mycotoxins. Adsorption must be as specific as possible so that essential molecules will not also be bound. Most of adsorbing agents, especially aluminosilicates, have been tested for

Detoxification of mycotoxins by transformation

Transformation by physical and chemical treatment

Few physical or chemical processes can transform mycotoxins into non-toxic products. Those most studied are presented below. In [START_REF] Kabak | Strategies to prevent mycotoxin contamination of food and animal feed: A review[END_REF], an interesting detailed review is available dealing with this topic. [START_REF] He | Chemical and biological transformations for detoxification of trichothecene mycotoxins in human and animal food chains: a review[END_REF] reviewed the chemical and biological transformations for detoxification of trichothecene mycotoxins.

Thermal treatment. Mycotoxins are generally very stable and can hardly be eliminated by thermic treatment [START_REF] Kabak | The fate of mycotoxins during thermal food processing[END_REF]. Little or no reduction in mycotoxin levels occurs as a result of normal cooking conditions such as boiling, frying. For example, DON is stable at 120°C, moderately stable at 180°C and partially stable at 210°C (WHO, 2001). Fumonisins are completly destroyed at 220°C [START_REF] Dupuy | Thermostability of fumonisin B1, a mycotoxin from Fusarium moniliforme, in corn[END_REF]. Torrefaction process could eliminate between 45 and 83% of aflatoxin content while panification or pasteurization is not efficient to remove aflatoxin (CAST, 2003). Thermal treatment on ZEA contaminated food is not efficient [START_REF] Ryu | Heat stability of zearalenone in an aqueous buffered model system[END_REF]. The initial level of contamination, type of mycotoxin and its concentration, heating temperature and time, the degree of heat penetration, the moisture content, pH, ionic strength of food play a significant role in the achievement of toxin degredation [START_REF] Rustom | Aflatoxin in food and feed: occurrence, legislation and inactivation by physical methods[END_REF].

Degradation by extrusion. Extrusion enables aflatoxins, DON, ZEA and FB1 to be removed from maize [START_REF] Cazzaniga | Mycotoxins inactivation by extrusion cooking of corn flour[END_REF][START_REF] Rustom | Aflatoxin in food and feed: occurrence, legislation and inactivation by physical methods[END_REF][START_REF] Voss | Reduced toxicity of fumonisin B1 in corn grits by single-screw extrusion[END_REF]. Extrusion implies molecular modifications such as protein denaturation and the inhibition of the enzymatic activity.

Radiation. Most mycotoxins have complex molecular structures and are not often affected by irradiation. Radiolysis of water produces free radicals that would react with mycotoxins [START_REF] Stepanik | Effects of electron beam irradiation on deoxynivalenol levels in distillers dried grain and solubles and in production intermediates[END_REF]. AFB1 is sensitive to UV, X and gamma rays. Radiation of AFB1 is able to reduce its level of contamination [START_REF] Rustom | Aflatoxin in food and feed: occurrence, legislation and inactivation by physical methods[END_REF][START_REF] Afifi | Effect of gamma irradiation on elimination of aflatoxins produced by apple mycoflora in apple fruits[END_REF]. Gamma radiation can also reduce microbial flora. Using micro-waves permit the reduction of aflatoxin content inpeanuts [START_REF] Farag | Aflatoxin destruction by microwave heating[END_REF] and trichotecenes in corn [START_REF] Scott | Industrial and farm detoxification processes for mycotoxins[END_REF].

Oxydation. Some oxidizing agents like ozone and hydrogen peroxyde have been used to render mycotoxin-contaminated feed harmless. Chemical oxidizing agents can react with numerous functional groups. [START_REF] Mayura | Prevention of maternal and developmental toxicity in rats via dietary inclusion of common aflatoxin sorbents: potential for hidden risks[END_REF] showed that a treatment of contaminated corn with electrochemically produced O 3 provided protection against AFB1 in young turkey poults. [START_REF] Canadas | Evaluation du procédé Oxygreen® pour son potentiel de décontamination en ochratoxine A du blé. Les effets toxiques liés à une exposition subchronique à l'ochratoxine A sont-ils atténués[END_REF] studied the efficacy of the Oxygreen® process using ozone on OTA-contaminated cereals. The Oxygreen® process permitted the reduction of microbiological and mycotoxin contamination but it seems to induce some side effects such as ADN adducts in wheat. Abd [START_REF] Alla | Zearalenone: Incidence, toxigenic fungi and chemical decontamination in Egyptian cereals[END_REF] [START_REF] Lemke | Assessment of the estrogenic effects of zearalenone after treatment with ozone utilizing the mouse uterine weight bioassay[END_REF] showing ozone could prevent the estrogenic effects of ZEA in mice. Biological activities of trichothecenes are also changed by oxidation. Ozone is most likely to attack the double bond in trichothecenes [START_REF] Mckenzie | Oxidative degradation and detoxification of mycotoxins using a novel source of ozone[END_REF].

Reduction. Reducing agents (ascorbic acid, NaHSO 3 , Na 2 S 2 O 5 ) permitting the reduction of such mycotoxins as AFB1 and DON [START_REF] Kabak | Strategies to prevent mycotoxin contamination of food and animal feed: A review[END_REF]. Sodium bisulfite transforming DON to DON-sulfonate, which is less toxic than DON, was reported to be an effective tool for overcoming the depressive effects of Don on feed-intake in piglets [START_REF] Dänicke | On the effects of a hydrothermal treatment of deoxynivalenol (DON)-contaminated wheat in the presence of sodium metabisulphite (Na 2 S 2 O 5 ) on DON reduction and on piglet performance[END_REF].

The reaction of FB1 with reducing sugars such as D-glucose, D-fructose at 65°C for 48h can block the primary amino group of FB1, and seems to prevent FB1-induced toxicity on cell tissue cultures on rats and swine (Fernandez-Surumay et al., 2005).

Ammoniation. Maize ammoniation, largely used to diminish the level of aflatoxins in feed is an efficient method for detoxifying feed that has been in use for several years [START_REF] Park | Review of the decontamination of aflatoxins by ammoniation: current status and regulation[END_REF]. This process is particularly effictive against AFB1 when carried out at high temperature and pressure. One of the degradation products is AFD1, less toxic than AFB1.

However, this costly method is not effective against other mycotoxins and can damage food quality because of an excessive level of ammonia in the food involved [START_REF] Huwig | Mycotoxin detoxification of animal feed by different adsorbents[END_REF].

Alkalization. Under alkaline conditions, mycotoxins structure can change. For example, under alkaline conditions, the 12-13 epoxy group of DON could be opened [START_REF] Bretz | Thermal degradation of the Fusarium mycotoxin deoxynivalenol[END_REF].

Acidification. Treatment of aflatoxins with strong acids destroys the biological activity of AFB1 converting them to the hemi-acetal form [START_REF] Heathcote | Aflatoxins : Chemical and biological aspect[END_REF]. Treatment with HCl (pH 2) has been shown to reduce AFB1 levels by 19.3% within 24h [START_REF] Doyle | Physical, chemical and biological degradation of mycotoxins in foods and agricultural commodities[END_REF].

Deamination. Adding NaNO 2 to an aqueous medium deaminates FB1 and so reduces its toxicity (Lemke et al., 2001b).

Transformation by microorganisms and enzymes

The use of chemical or physical processes to decontaminate food is limited by high costs, a loss of food's nutritional quality, poor efficiency, low specificity and consumer reticence toward chemical methods. Thus, scientists have come to favor the detoxification of mycotoxins by biological transformation which can be defined as the degradation or enzymatic transformation of mycotoxins (by full microorganisms or enzymes) in less toxic compounds.

A wide range of microorganisms belonging to the bacteria, moulds and yeasts have shown their capacity to biotransform mycotoxins. Such microbes act in the intestinal tract of animals prior to the resorption of the mycotoxins.

AFB1 transformation. Removal and detoxification of AFB1 by transformation have been investigated for many years. Unfortunately, few studies have led to the identification of the transformed product. One of the first bacteria studied for its capacity to remove AFB1 was Flavobacterium aurantiacum (also known as Nocardia corynebacteriodes). Its crude extract was shown to remove AFB1 [START_REF] Ciegler | Microbial Detoxification of Aflatoxin[END_REF][START_REF] Hao | Growth and survival of Flavobacterium Aurantiacum in peanut Milk[END_REF]. Further studies had shown that the transformation did not lead to a toxic product [START_REF] Lillehoj | Aflatoxin B1 Uptake by Flavobacterium Aurantiacum and Resulting Toxic Effects[END_REF] and that an intracellular enzyme was involved [START_REF] Smiley | Preliminary evidence that degradation of aflatoxin B1 by Flavobacterium aurantiacum is enzymatic[END_REF]. [START_REF] Guan | Aflatoxin B(1) degradation by Stenotrophomonas maltophilia and other microbes selected using coumarin medium[END_REF] succeeded in obtaining Stenotrophomonas maltophilia isolates on selective medium containing only coumarin (chemical component of AFB1 nucleus) as the carbon source and showed that it is capable of transforming AFB1. Bacillus subtilis was also able to detoxify AFB1-contaminated feed and thus facilitate animal growth rate [START_REF] Kubo | Animal feed containing Bacillus subtilis FERM BP-3418 that decomposes aflatoxin[END_REF][START_REF] Petchkongkaew | Isolation of Bacillus spp. from Thai fermented soybean (Thua-nao): screening for aflatoxin B-1 and ochratoxin A detoxification[END_REF]. Actinomyceta like Mycobacterium fluoranthenivorans was shown to remove AFB1 from contaminated media [START_REF] Hormisch | Mycobacterium fluoranthenivorans sp nov., a fluoranthene and aflatoxin B-1 degrading bacterium from contaminated soil of a former coal gas plant[END_REF][START_REF] Teniola | K-4GSJPX5-1&_user=10&_coverDate=11%2F25%2F2005&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d& _docanchor=&view=c&_searchStrId=1587022348&_rerunOrigin=google&_acct=C[END_REF]. [START_REF] Teniola | K-4GSJPX5-1&_user=10&_coverDate=11%2F25%2F2005&_rdoc=1&_fmt=high&_orig=search&_origin=search&_sort=d& _docanchor=&view=c&_searchStrId=1587022348&_rerunOrigin=google&_acct=C[END_REF] succeeded in isolating extracellular enzymes from Rhodococcus erythropolis, responsible for the transformation of AFB1. Moreover, [START_REF] Alberts | Biological degradation of aflatoxin B-1 by Rhodococcus erythropolis cultures[END_REF] observed the elimination of toxicity using the Ames test after transformation. [START_REF] Nakazato | Interconversion of Aflatoxin-B1 and Aflatoxicol by Several Fungi[END_REF] and later [START_REF] Shantha | Fungal degradation of aflatoxin B1[END_REF] observed the removal of AFB1 by moulds but no transformation product was observed. Extracellular enzymes from the macroscopic fungus Pleurotus ostreatus were shown to be able to cleave the AFB1 lactone ring [START_REF] Motomura | Purification and characterization of an aflatoxin degradation enzyme from Pleurotus ostreatus[END_REF] leading to a loss of toxicity. Armillariella tabescens is able to open the AFB1 difuran cycle [START_REF] Liu | Detoxification of aflatoxin B-1 by enzymes isolated from Armillariella tabescens[END_REF][START_REF] Liu | Production, purification, and characterization of an intracellular aflatoxin-detoxifizyme from Armillariella tabescens (E-20)[END_REF].

OTA transformation. Certain bacteria, moulds, yeasts and plants are able to transform OTA. Amoung these microorganisms, many transform OTA into OTα [START_REF] Galtier | In vitro transformation of ochratoxin A by animal microbioal floras[END_REF][START_REF] Kiessling | Metabolism of aflatoxin, ochratoxin, zearalenone, and three trichothecenes by intact rumen fluid, rumen protozoa, and rumen bacteria[END_REF][START_REF] Hwang | Degradation of ochratoxin A by Acinetobacter calcoaceticus[END_REF][START_REF] Wegst | Bacterial degradation of ochratoxin A[END_REF][START_REF] Skrinjar | Lowering of ochratoxin A level in milk by yoghurt bacteria and bifidobacteria[END_REF]Abrunhosa et al., 2002;[START_REF] Péteri | Ochratoxin degradation and adsorption caused by astaxanthin-producing yeasts[END_REF], a less toxic compound. This transformation leads to a formation of phenylalanine (Figure 1). Moulds like Aspergillus, Rhyzopus, Penicillium species are particularly effictive at removing OTA (Abrunhosa et al., 2002;[START_REF] Bejaoui | Black aspergilli and ochratoxin A production in French vineyards[END_REF][START_REF] Varga | Degradation of ochratoxin A by Aspergillus species[END_REF]. Aureobasidium pullulans was used as a biocontrol agent in wine, preventing OTA accumulation in grapes and decreasing the aspergillosis symptom [START_REF] De Felice | Strains of Aureobasidium pullulans can lower ochratoxin A contamination in wine grapes[END_REF]. Plants like wheat and maize [START_REF] Ruhland | Transformation of the mycotoxin ochratoxin A in plants .2. Time course and rates of degradation and metabolite production in cellsuspension cultures of different crop plants[END_REF] or fungi like P. ostreatus [START_REF] Engelhardt | Degradation of ochratoxin a and b by the white rot fungus Pleurotus ostreatus[END_REF] are able to remove OTA but no transformation products have been identified. Trichosporon mycotoxinivorans is a microorganism that has been developed into a commercial product for detoxifying OTA in animal feed [START_REF] Molnar | Trichosporon mycotoxinivorans sp nov., a new yeast species useful in biological detoxification of various mycotoxins[END_REF].

Total transformation of OTA to OTα occurred in 2.5 h. Moreover, [START_REF] Schatzmayr | Investigation of different yeast strains for the detoxification of ochratoxin A[END_REF][START_REF] Schatzmayr | Microbiologicals for deactivating mycotoxins[END_REF] showed that the toxic effects of OTA could be alleviated by the addition of this yeast to chicken diet. The main microorganisms which transform OTA into Otα use carboxypeptidases (EC 3.4.17.1). Purified enzymes are able to cleave OTA and have been characterized [START_REF] Stander | Screening of commercial hydrolases for the degradation of ochratoxin A[END_REF][START_REF] Abrunhosa | Degradation of ochratoxin A by proteases and by a crude enzyme of Aspergillus niger[END_REF].

ZEA transformation. ZEA can be transformed into an oxydised compound such as zearalanone, hydroxyl such as α and β ZEA, methyl compounds, gluco-or sulfo-conjugates and hydrolysed compounds (Table 1) by bacteria, yeasts, moulds or plants (El-Sharkawy and Abul-Hajj;1987a, b, 1988). The transformation of ZEA to α-zéaralénol [START_REF] Mcmullen | Microbiological reduction of zearalenone and related compounds[END_REF][START_REF] Kiessling | Metabolism of aflatoxin, ochratoxin, zearalenone, and three trichothecenes by intact rumen fluid, rumen protozoa, and rumen bacteria[END_REF][START_REF] Kamimura | Conversion of zearalenone to zearalenone glycoside by Rhizopus sp[END_REF][START_REF] Böswald | Metabolism of the Fusarium mycotoxins zearalenone and deoxynivalenol by yeast strains of technological relevance[END_REF] does not lead to actual detoxification since this product has an oestrogenic activity even higher than that of ZEA (Minervini et al., 2005[START_REF] Fitzpatrick | Measurement of the relative affinity of zearalenone, alpha-zearalenol and beta-zearalenol for uterine and oviduct estrogen receptors in swine, rats and chickens: an indicator of estrogenic potencies[END_REF]. A proteic sequence of a ZEA esterase transforming ZEA into decarboxylated ZEA from a Rhodococcus or Nocardia species has been patented for insertion in transgenic plants [START_REF] Duvick | Zearalenone detoxification compositions and methods[END_REF][START_REF] Karlovsky | Compositions and methods of zearalenone detoxification[END_REF]. Trichosporon mycotoxinivorans is also able to decarboxylate ZEA [START_REF] Molnar | Trichosporon mycotoxinivorans sp nov., a new yeast species useful in biological detoxification of various mycotoxins[END_REF][START_REF] Vekiru | Cleavage of Zearalenone by Trichosporon mycotoxinivorans to a Novel Nonestrogenic Metabolite[END_REF]. Some conjugates can also be formed from ZEA, such as ZEAglucoside (El- Sharkawy and Abul-Hajj, 1987a;[START_REF] Kamimura | Conversion of zearalenone to zearalenone glycoside by Rhizopus sp[END_REF] and ZEA-sulfate (El [START_REF] Sharkawy | Microbial transformation of zearalenone to a zearalenone sulfate[END_REF][START_REF] Plasencia | Isolation and Characterization of Zearalenone Sulfate Produced by Fusarium Spp[END_REF]. Recently, [START_REF] Jard | Transformation of zearalenone to zearalenone sulfate by Aspergillus sp[END_REF], using a MCF-7 cell line, showed that ZEA sulfonation leads to a reduction in oestrogenic toxicity.

This confirms the study done by [START_REF] Plasencia | Isolation and Characterization of Zearalenone Sulfate Produced by Fusarium Spp[END_REF], using the uterus weight test, showing a decline in toxicity by ZEA sulfonation. However, it has not been proven that sulfonation or glycosylation leads effectively to a detoxification insofar as hydrolysis of this conjugate could occur in the digestive tract. Moreover, plants are able to transform ZEA into ZEA-glycoside [START_REF] Schneweis | Occurrence of zearalenone-4-beta-Dglucopyranoside in wheat[END_REF] leading to masked mycotoxins which could not be measured but could be released by feeding with contaminated plants. Other degradation products have been observed, including decarboxylated and hydrolysed compounds (El- [START_REF] Sharkawy | Microbial clivage of zearalenone[END_REF][START_REF] Kakeya | Biotransformation of the mycotoxin, zearalenone, to a non-estrogenic compound by a fungal strain of Clonostachys sp[END_REF][START_REF] Takahashi-Ando | A novel lactonohydrolase responsible for the detoxification of zearalenone: enzyme purification and gene cloning[END_REF][START_REF] Igawa | Reduced contamination by the Fusarium mycotoxin zearalenone in maize kernels through genetic modification with a detoxification gene[END_REF][START_REF] Duvick | Zearalenone detoxification compositions and methods[END_REF][START_REF] Karlovsky | Compositions and methods of zearalenone detoxification[END_REF]. The corresponding gene of this enzymatic activity was cloned and transfered to different organisms like yeast [START_REF] Takahashi-Ando | Efficient decontamination of zearalenone, the mycotoxin of cereal pathogen, by transgenic yeasts through the expression of a synthetic lactonohydrolase gene[END_REF] and plants [START_REF] Kakeya | Biotransformation of the mycotoxin, zearalenone, to a non-estrogenic compound by a fungal strain of Clonostachys sp[END_REF][START_REF] Takahashi-Ando | A novel lactonohydrolase responsible for the detoxification of zearalenone: enzyme purification and gene cloning[END_REF][START_REF] Igawa | Reduced contamination by the Fusarium mycotoxin zearalenone in maize kernels through genetic modification with a detoxification gene[END_REF]. [START_REF] Utermark | Role of zearalenone lactonase in protection of Gliocladium roseum from fungitoxic effects of the mycotoxin zearalenone[END_REF] showed that ZEA lactonohydrolase from Clonostachys rosea [START_REF] Sharkawy | Microbial clivage of zearalenone[END_REF] prevents the growth inhibition observed for others types of fungi growing on ZEA-contaminated media. [START_REF] Gromadzka | Solid substrate bioassay to evaluate the effect of Trichoderma and Clonostachys on the production of zearalenone by Fusarium species[END_REF] showed that this fungus could be used as a biocontrol agent for mycotoxin production in cereals. Pseudomonas sp., bacteria from soil are able to remove ZEA [START_REF] El-Deeb | Isolation and characterization of soil bacteria able to degrade zearalenone[END_REF].

The product was not identified but was assumed to be less toxic than ZEA. [START_REF] Megharaj | Total biodegradation of the oestrogenic mycotoxin zearalenone by a bacterial culture[END_REF] showed that a mixed culture from soil was able to remove ZEA. No transformation product was observed. An unidentified bacterium from pig intestine was also able to remove ZEA [START_REF] Kollarczik | In vitro transformation of the Fusarium mycotoxins deoxynivalenol and zearalenone by the normal gut microflora of pigs[END_REF]. Some microorganisms have the capacity to remove ZEA producing different derived compounds. For example, El [START_REF] Sharkawy | Microbial transformation of zearalenone to a zearalenone sulfate[END_REF] identified 26% of ZEA-sulfate and 18% of α-ZOL after a ZEA transformation by Rhyzopus. An enzyme from Pseudomonas sp. responsible for the transformation into a less toxic product is encoded by a plasmid [START_REF] Skrinjar | Lowering of ochratoxin A level in milk by yoghurt bacteria and bifidobacteria[END_REF]. [START_REF] Cheng | Toxicity of different Fusarium mycotoxins on growth performance, immune responses and efficacy of a mycotoxin degrading enzyme in pigs[END_REF] studied an enzyme able to transform ZEA but its origin and transformation product(s) are unknown. [START_REF] Zhou | Microbial transformation of trichothecene mycotoxins[END_REF] and [START_REF] He | Chemical and biological transformations for detoxification of trichothecene mycotoxins in human and animal food chains: a review[END_REF]. The 12,13-epoxy cycle of DON and of T-2 toxin seems to be the part of the molecule which is responsible for the toxicity. By opening this cycle, the mycotoxin become less toxic [START_REF] Swanson | The role of intestinal microflora in the metabolism of trichothecene mycotoxins[END_REF][START_REF] Zhou | Microbial transformation of trichothecene mycotoxins[END_REF]. Some studies report a transformation of DON by mixed cultures of microorganisms but few of these have been identified. The two main metabolites are de-epoxydised DON [START_REF] Kollarczik | In vitro transformation of the Fusarium mycotoxins deoxynivalenol and zearalenone by the normal gut microflora of pigs[END_REF][START_REF] Young | Degradation of trichothecene mycotoxins by chicken intestinal microbes[END_REF][START_REF] Yoshizawa | Structure of a novel metabolite from deoxynivalenol, a trichothecene mycotoxin, in animals[END_REF][START_REF] Côté | Production of deepoxydeoxynivalenol (DOM-l), a metabolite of deoxynivalenol, by in vitro rumen incubation[END_REF][START_REF] He | Microbial transformation of deoxynivalenol (vomitoxin)[END_REF][START_REF] Swanson | The role of intestinal microflora in the metabolism of trichothecene mycotoxins[END_REF][START_REF] King | Transformation of deoxynivalenol (vomitoxin) by rumen microorganisms[END_REF] and 3-keto-DON [START_REF] Young | Degradation of trichothecene mycotoxins by chicken intestinal microbes[END_REF][START_REF] Binder | Strain of Eubacterium that detoxyfies trichothecenes[END_REF][START_REF] Shima | Novel detoxification of the trichothecene mycotoxin deoxynivalenol by a soil bacterium isolated by enrichment culture[END_REF]. The chemical structures of these DON metabolites are presented on Table 2. Both are less toxic than DON. For example, [START_REF] Shima | Novel detoxification of the trichothecene mycotoxin deoxynivalenol by a soil bacterium isolated by enrichment culture[END_REF] observed a weaker immunosuppressive activity for 3-keto-4-DON produced by Agrobacterium-Rhizobium E 3-39 than for DON.

The Eubacterium sp. strain BBSH 797 has been developed into a commercial product Mycofix plus (Biomin®) for detoxifying trichothecenes in animal feed [START_REF] Schatzmayr | Microbiologicals for deactivating mycotoxins[END_REF]. An enzyme named MDE (mycotoxin-degrading enzyme), whose origin is not specified is able to degrade DON with ZEA [START_REF] Cheng | Toxicity of different Fusarium mycotoxins on growth performance, immune responses and efficacy of a mycotoxin degrading enzyme in pigs[END_REF]. Some transformation products have not yet been identified [START_REF] Binder | Strain of Eubacterium that detoxyfies trichothecenes[END_REF][START_REF] Völkl | Microbial detoxification of mycotoxin deoxynivalenol[END_REF][START_REF] Guan | Transformation of trichothecene mycotoxins by microorganisms from fish digesta[END_REF].

Among these transformations, one was done by a bacterium from fish intestine, achieving 100% removal in 96h.

Few studies exist concerning the transformation of T-2 and HT-2 toxins. Some metabolites were identified to be de-acetylate and de-epoxydised T-2 (Table 3). Some microorganisms were able to transform T-2 toxin into HT-2 toxin but this did not lead to detoxification [START_REF] Fuchs | Structural characterization of metabolites after the microbial degradation of type A trichothecenes by the bacterial strain BBSH 797[END_REF][START_REF] Swanson | The role of intestinal microflora in the metabolism of trichothecene mycotoxins[END_REF]. Bacteria isolated by enrichment from contaminated soil or water can transform T-2 toxin into T-2 triol and T-2 tetraol [START_REF] Beeton | Biotransformation and detoxification of T-2 toxin by soil and freshwater bacteria[END_REF]. A similar transformation was observed for carboxyl esterase isolated from rat liver [START_REF] Johnsen | Metabolism of T-2 toxin by rat liver carboxylesterase[END_REF]. Some moulds can transform T-2 toxin but the transformation products were not identified [START_REF] Jesenska | T-2 toxin degradation by micromycetes[END_REF]. The metabolism of T-2 toxin was elucidated by [START_REF] Swanson | The role of intestinal microflora in the metabolism of trichothecene mycotoxins[END_REF] and [START_REF] Beeton | Biotransformation and detoxification of T-2 toxin by soil and freshwater bacteria[END_REF]. It includes a sequence of different steps: the molecule is first transformed into HT-2 toxin by deacetylation. A second deacetylation was observed to transform HT-2 toxin into T-2 triol, 20 times less toxic than the T-2 toxin [START_REF] Ueno | Metabolism of T-2 toxin in Curtobacterium sp. strain 114-2[END_REF]. Finally, this molecule is transformed into T-2 tetraol. Other metabolites observed are the de-epoxyed metabolites cited previously (Table 3). maize, as the plant became resistant to fumonisine [START_REF] Duvick | Fumonisin detoxification compositions and methods[END_REF]. Other enzymes are involved in FB1 degradation and some derived products have been characterised [START_REF] Blackwell | Oxidative deamination of hydrolyzed fumonisin B(1) (AP(1)) by cultures of Exophiala spinifera[END_REF]. A patent was taken out in 2003 [START_REF] Duvick | Fumonisin detoxification compositions and methods[END_REF] for esterase used to detoxify fumonisines.

Conclusion

Although there are many publications on the removal of mycotoxins by adsorption and transformation, their applications in detoxification have been limited.

Chemical treatment for the detoxification of aflatoxins using ammonia is the only application currently licensed in the United States. Chemical treatment is not allowed within the European Union for products used by humans (EU Commission Regulation, 2001). Recourse to chemical transformation may lead to toxic derivatives in the treated products. These sideeffects limit their use in the human and animal food chains [START_REF] Kabak | Strategies to prevent mycotoxin contamination of food and animal feed: A review[END_REF] with the decreased interest in chemical transformations, interest has been increasingly focused on adsorption or transformation of mycotoxins. Adsorption by yeast cell walls added to feed is used most commonly in the industrial context. Legislation is changing to allow the marketing of mycotoxin binders. Up to now, these products have been sold for other applications such as increasing antioxydising activity. It has proved difficult for governments to legislate on this topic without encouraging suppliers to sell contaminated commodities. Mycotoxin adsorption is quite well documented and was tested in vitro in a gastrointestinal tract which has enabled us to better determine the stability of the binder-mycotoxin complex (Avantaggiatto et al., 2004(Avantaggiatto et al., , 2007)).

Transformation of mycotoxins for detoxification is not much used in industry. This may be due to the lack of information about the transformation mechanisms, the toxicity of products derived from transformation, and the effect of transformation reactions on the nutritional value of food and feed. In some cases, transformation products have not been identified and so cannot be used in industrial processes. The stability of transformations and their potential side-effects should be investigated. Indeed, the use of a microorganism for detoxifying mycotoxins in feed requires the observance of certain conditions:

-The first step is identification of a microorganism's degradation potential;

-Each product must be identified and its toxicity must be tested, using different methods if possible;

-Derived products must be non-toxic; -Biotransformation must be fast and microorganisms must be efficient at different levels of oxygen or pH, especially when transformation takes place during digestion; -Microorganisms must be non-pathogenic; -Microorganisms must be active in a complex environment and not inhibited by nutrients; The use of microbial detoxification agents (living cells) in the human food and animal feed industries seems to be diminishing on account of regulatory, toxicological and consumer considerations. Thus, applications of detoxification enzymes and genes can represent alternative detoxification methods. Some interesting studies have been carried out using molecular engineering techniques to obtain genes [START_REF] Takahashi-Ando | Metabolism of zearalenone by genetically modified organisms expressing the detoxification gene from Clonostachys rosea[END_REF]. Such genes were obtained, cloned and incorporated into microorganisms to produce recombinant enzymes that are suitable for industrial-scale enzyme production and purification (Althali and Deeb, 2009).

Today, chemical transformation is no longer suitable for detoxifying mycotoxin-contaminated food and feed. Mycotoxin binding may be a feasible industrial solution because of its relative low cost compared to biotransformation. However, this technique can lead to negative sideeffects. Indeed, adsorption could be reversible as a mycotoxin could desorb in the digestive tract, and adsorption can be non-specific thus decreasing overall nutritional value (Phillips et al., 2008). Mycotoxin transformation appears to offer great interest as a technique for increasing the quality of food and feed. Studies involving biotransformation have led to encouraging results. But, further studies must be done to ensure the safety of this method.

The transformation of mycotoxins in food and feed promises to be a very reliable technique for enhancing food safety and eliminating all negative effects of the mycotoxins present.

  of mycotoxin removal. It could provide insight in the detoxification in mycotoxin present in food and feed.

  IntroductionMycotoxins are secondary metabolites produced by filamentous fungi that cause a toxic response (mycotoxicosis) when ingested by animals. Plants can be contaminated in two

  contamination of feed by mycotoxins: substances that can suppress or reduce the absorption, promote the excretion of mycotoxins or modify their mode of action" was defined by the Commission regulation (EC) No 386/2009 of 12 May 2009. Depending on their mode of action, these feed additives may act by reducing the bioavailability of the mycotoxins or by degrading them or transforming them into less toxic metabolites.

  Activated charcoal is formed by the pyrolysis of organic materials. It is a general adsorptive material with a large surface area and excellent adsorptive capacity.

  same time reducing the impact on nutritional quality compared to mineral adsorbents.

  bind aflatoxins. The mycotoxins targeted by yeast cell wall, bacteria and other adsorbing agents are more diverse.

  Trichothecenes transformation by microorganisms was reviewed by

Fumonisin

  B1 transformation. The primary amine of FB1 confers its toxicity. The deamination of this molecule greatly reduces its toxicity. Very few studies have been done on the biological degradation of FB1. The main microorganism able to degrade FB1 is the black yeast Exophiala spinifera. The different metabolites produced by this yeast are presented in Table4. The transformation of FB1 into AP1 is performed by an extracellular carboxylesterase. This enzyme has been cloned and was shown to be efficient in transgenic

-

  The efficiency of the transformation must be assessed in vivo.

  Figure 1: Transformation of OTA to Otα and phenylalanine 159x24mm (96 x 96 DPI)

  revealed that ZEA was degraded by 83.9% when

	using 10% H 2 O 2 at 80°C for 16h. It was confirmed by
	F o r
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http://mc.manuscriptcentral.com/tfac Email: fac@tandf.co.ukFood Additives and Contaminants

Acknowledgements

The authors especially thank "Evialis" (Saint-Nolff, France) for its financial support.


Benjamin Pigeau
email: benjamin.pigeau@cea.fr

Christian Hahn

G De Loubens

V V Naletov

Olivier Klein

Kaname Mitsuzuka

M Hehn

S Andrieu

Daniel Lacour

F Montaigne

Measurement of the dynamical dipolar coupling in a pair of magnetic nano-disks using a Ferromagnetic Resonance Force Microscope

come   L'archive ouverte pluridisciplinaire

Studies of the collective dynamics in magnetic nanoobjects coupled by the dipolar interaction has recently attracted a lot of attention [1][2][3][4][5][6][7][8] due to its potential for creating novel properties and functionalities for the information technology. It affects the writing time of closely packed storage media [9], the synchronization of spin transfer nano-oscillators [10], and more broadly the field of magnonics [11], which aims at using spin-waves (SW) for information process [12]. Despite the generic nature of the dynamic magneto-dipolar interaction, which is present in all ferromagnetic resonance phenomena, its direct measurement has been elusive because it is difficult to reach a regime where this coupling is dominant. It requires that the strength of the dynamical coupling Ω exceeds both the deviation range of eigen-frequencies between coupled objects and the resonance linewidth.

Large Ω are usually obtained by fabricating nano-objects having large magnetization and placed nearby. But the constraint of fabricating two nano-objects, whose SW modes both resonate within Ω, is difficult to meet. For long wavelengths, the SW eigen-frequency is indeed very sensitive to imperfections in the confinement geometry, inherent to uncertainties of the nano-fabrication process. Moreover, a direct determination of the coupling strength between any two systems, as for instance a superconducting qubit and electronic spins [13], requires the ability to tune and detune them at least on the Ω-range. So far, the absence of a knob to do so with the individual frequencies of nearby magnetic objects has prevented a reliable measurement of the dynamical dipolar coupling.

In this paper we shall demonstrate that ferromagnetic resonance force microscopy (f-MRFM) allows this quantitative measurement of Ω. We shall rely on the field gradient of the magnetic tip as a mean to fully tune and detune the resonance frequencies of two nano-disks by continuously moving the tip laterally above the pair of disks. One can find a position where the stray field of the tip exactly compensates the deviation of internal field due to the patterning process. At this position, the splitting between the eigen-frequencies of the binding and anti-binding modes is exactly equal to the dynamical dipolar coupling Ω. By studying Ω as a function of the separation between the nano-disks, we shall demonstrate that f-MRFM provides a reliable mean to measure the strength of the dynamical coupling. It provides also a reliable mean to measure mode hybridization and mode linewidth.

The magnetic material used for this study is a t = 26.7 nm thick Fe-V (10% V) film grown by molecular beam epitaxy on MgO(001) [14,15]. This is a ferromagnetic alloy with a very high magnetization, 4πM s = 1.7 × 10 4 G, and a very low magnetic Gilbert damping, α = 2 × 10 -3 . The film is patterned into disks by ebeam lithography and ion milling techniques. The geometrical pattern (image in FIG. 1a) consists in three pairs of nearby disks having the same nominal diameter 2R = 600 nm but different edge to edge separation: s = 200 nm, 400 nm and 800 nm. Each set is separated by 3 µm in order to avoid cross coupling. An isolated disk of identical diameter is also patterned for reference purpose. The sample is then placed in the room temperature bore of an axial superconducting magnet. The disks are perpendicularly magnetized (z-axis) by an external field of 1.72 Tesla [16]. This field is sufficient to saturate all the disks. A linearly polarized (y-axis) microwave field h rf is produced by a broadband Au strip-line antenna of width 5 µm deposited on top of a 50 nm thick Si 3 O 2 isolating layer, above the magnetic disks. The f-MRFM experiment consists in detecting the mechanical motion produced by the magnetization dynamics in the Fe-V nano-disks of a Biolever cantilever with an Fe nanosphere of diameter 700 nm glued at its apex (see FIG. 1a) FIG. 1. a) Schematic of the f-MRFM setup: an Fe sphere glued at the apex of a soft cantilever is scanned laterally above different pairs of Fe-V disks excited by a microwave field. b) Density plot of the f-MRFM signal as a function of the displacement x of the sphere above an isolated disk. The inset is a SEM image of the 2R = 600 nm Fe-V disk (green) placed below the microwave antenna (gold). [17]. We will consider in the following that the stray field of the tip H sph reduces to the dipolar field created by a punctual magnetic moment m sph = 3 × 10 -10 emu placed at the center of the sphere. The role of the magnetic tip in f-MRFM is to create a field gradient tensor G = ∇H sph on the sample in order to spatially code the resonance frequency and to provide a local detection [18].

These two features are illustrated by FIG. 1b, which shows the dependence of the f-MRFM signal measured above the isolated disk as a function of the position of the tip on the x-axis. It displays the behavior of the lowest energy SW mode, where all spins are precessing in phase at the Larmor frequency around the unit vector ẑ. The cantilever is scanned at constant height h above the sample surface. The position x = 0 corresponds to placing the probe on the axis of the disk.

We first concentrate on the variation of the FMR resonance frequency as a function of the x-position of the sphere. It displays a bell curve, whose shape is due to the additional bias field produced by the tip

ω(x) = ω FMR + γ{H sph,z (x)} , (1)
where the first term is the resonance frequency in the absence of the sphere and the second term is the gyromagnetic ratio γ times the spatial average of the z-component of the stray field of the sphere over the disk volume.

The curly bracket indicates that this average should be weighted by the spatial profile of the lowest energy SW mode [19]. The maximum shift of frequency occurs close to x = 0, where the additional field from the f-MRFM sphere is maximal [START_REF]The asymmetries of the bell-shape curve (maximum of frequency shifted with respect to x = 0 and to the maximum of amplitude, and different slopes in the wings) are due to the misalignment θH[END_REF]. The slope of the wings is proportional to the lateral field gradient G zx . For h ≫ 2R, it is maximum at x ≃ 0.39 h, where h is the height between the sample surface and the sphere center. At this location, the gradient is about G zx ≈ 2.7 m sph /h 4 . Since it is important to keep h as large as possible for stability purpose, the optimal h is reached when γG zx R > Ω. For our settings, this occurs at h = 1.8 µm, leading to slope of about 0.3 GHz/µm. At this distance, the maximum stray field of the sphere is about 140 G, a small variation compared to the static perpendicular field of 1.72 T, ensuring that no significant deformation of the SW modes profile is induced [17].

We then turn to the variation of the amplitude of the f-MRFM signal as a function of the position of the sphere in FIG. 1b. The force acting on the cantilever can be calculated as the vertical force exerted by the tip on the sample, F z = G zz ∆M z , where ∆M z is the variation of the sample magnetization induced by the FMR resonance [17]. The gradient G zz decays as the power 1/x 5 , for large lateral displacement x. This decay ensures a local detection. Experimentally, the signal decreases by one order of magnitude when the probe is displaced by 1.2 µm laterally.

We now discuss the same experiment above the pair of two 600 nm disks separated by s = 200 nm. The result is displayed on FIG. 2a. Here x = 0 corresponds to the middle of the pair. At each position x of the f-MRFM probe, we can see two modes. The upper branch has two frequency maxima at x 1,2 = ∓400 nm, whose separation corresponds to the center to center distance between disk 1 and disk 2. The two maxima occur at slightly different frequencies, presumably due to a small difference in diameter between the two disks. When the probe is placed in between, x 1 < x < x 2 , the two levels anti-cross, which is a characteristic behavior of a coupled dynamics. Defining ω 1,2 as the frequencies of the two uncoupled disks, the collective frequencies follow:

ω A,B = ω 1 + ω 2 2 ± ω 1 -ω 2 2 2 + Ω 2 2 (2)
with Ω being the dynamical coupling strength. The two coupled eigen-frequencies ω A,B correspond respectively to the anti-binding mode (A), where spins are precessing out-of-phase between the two disks, and to the binding mode (B), where spins are precessing in-phase [START_REF] Naletov | [END_REF]. In our f-MRFM experiment, ω 1,2 both depend on x, see Eq.1:

ω 1,2 (x) = ω FMR +γ{H sph,z (x-x 1,2 )}.
Using these dependencies in Eq.2, one can obtain an analytical expression for the frequency difference ω A (x) -ω B (x) observed in FIG. 2. At x = 0, when ω 1 = ω 2 , the splitting ω A -ω B exactly measures Ω. Using this analytical expression for the spatial dependence of the splitting, we have fitted Ω/2π = 50 ± 5 MHz. We emphasize that this splitting is 2.5 times larger than the linewidth, found to be 20 MHz. Theoretically, the coupling Ω for the magneto-dipolar interaction is defined by [START_REF] Naletov | [END_REF]]

Ω 2 = 4γ 2 h 1,2 h 2,1 . (3)
h i,j represents the cross depolarization field produced by the SW in the j-th disk on the i-th disk (i, j = 1, 2) [22,23]. It can be expressed as a function of the cross depolarization tensor elements, which have an analytical expression in the approximation of a uniform precession [24]: h i,j = 2πM s ({N i,j xx }+{N i,j yy }). This formula reflects that the magneto-dipolar interaction is anisotropic and thus, it induces an elliptical precession in the two disks. For the separation s = 200 nm, a numerical application yields {N 1,2 xx } ≈ -2{N 1,2 yy } ≈ 0.0012, which corresponds to a coupling field of about 10 G between the two disks, or a coupling frequency Ω/2π = 56 MHz, in very good agreement with the measured value.

Another striking feature in FIG. 2a is the strong variation of the signal amplitude near the optimum coupling. We have explicitly plotted in FIG. 3a the amplitude of the f-MRFM signal as a function of the lateral displacement x of the probe, showing both the near extinction of the anti-binding mode (A) and the strong enhancement of the binding mode (B) near x = 0. The ratio of hybridization in the two coupled disks follows the expression:

c 1 c 2 A,B = (ω 1 -ω 2 ) ∓ (ω 1 -ω 2 ) 2 + Ω 2 Ω ∓1 (4)
Introducing the spatial dependence of ω 1,2 described by Eq.1 in Eq.4 we can calculate the total force

F z ∝ P c 2 1 G zz (x -x 1 ) + c 2 2 G zz (x -x 2 )
acting on the cantilever. The power efficiency

P = |c 1 + c 2 | 2 h 2
rf is proportional to the overlap integral between the uniform rf field and the collective SW mode (the vector sum of the transverse magnetization in the two disks) [START_REF] Naletov | [END_REF]. Using Eq.4, the dependence on x of the force produced by the binding and anti-binding mode gives the continuous lines shown in FIG. 3a. The difference between the two curves comes mainly from the selection rules defined in P . We find that at the optimum coupling (when ω 1 and ω 2 cross), the anti-binding mode (A) in Eq.4 has c 1 = -c 2 , i.e., a precession with equal hybridization weight between the two disks and out-of-phase. The overlap with the uniform rf field excitation is thus zero at x = 0, leading to a vanishing amplitude. In contrast, the binding mode (B) has c 1 = +c 2 at the anti-crossing, i.e., a precession with equal hybridization weight too, but now in-phase between the two disks. It represents and enhancement of the absorbed power by a factor of 2 2 compared to the amplitude in one disk.

We then study the effect the magneto-dipolar coupling on the linewidth of the collective mode. We observe that the linewidth does not change much with tuning and the observed variation with x is below the 5% range. At the optimal tuning x = 0, the linewidth measured is ∆f = 22.3 ± 0.5 MHz (see FIG. 3b) and it becomes slightly larger ∆f = 23.1 ± 0.5 MHz at the maximum detuning x = x 1,2 . For comparison we have displayed in FIG. 3c the linewidth observed above the single disk, whose value ∆f = 21.4 ± 0.5 MHz. A small increase of the ratio ∆f /f is indeed expected for the dynamically coupled modes. This comes from the fact that this ratio is equal to ∆f /f = α(H x + H y )/ H x H y , where α is the Gilbert damping, and H x and H y represent the two stiffness fields which characterize the torque exerted on the magnetization when it is tipped along the x-or y-axis [START_REF] Gurevich | Magnetization Oscillations and Waves[END_REF]. The degree of hybridization as well as the nature of the mode (A or B) change the values and signs of H x and H y . For the binding mode, the magneto-dipolar coupling generates an elliptical precession whose long axis is along the two disks axis. The induced ellipticity E is maximum at the anti-crossing (x = 0), with an amplitude

E = β-1 β+1 Ω ωB ≈ 3%, with β = {N 1,2 xx }/{N 1,2 yy } ≈ -2.
An increase of ellipticity induces an increase of the linewdith, a behavior which is consistent with the small additional broadening measured in our experiment.

The analytical model used above to analyze the data In this color representation, the hue indicates the phase (or direction) of the oscillating magnetization, while the brightness indicates its amplitude. The simulation results confirm very nicely the interpretation made above in terms of amplitude and peak position.

We have then repeated the same procedure on the two other pairs of disks, with larger edge to edge separation s. The strength of the dynamical coupling measured by f-MRFM is plotted as a function of s in FIG. 4. The main results is that, with our experimental parameters, s needs to be less than the diameter of the disks in order to have Ω larger than the linewidth ∆f . The data are plotted along with the analytical prediction (continuous line) and the simulations (dashed line with small dots). We observe an excellent overall agreement between the three sets of results, which all exhibit a similar decay with s (not a simple polynomial law [START_REF] Sukhostavets | [END_REF]). Still, the ex-FIG. 4. Coupling strength as a function of the separation s between two disks. The plot compares the experimental findings to the predicted amplitude of the magneto-dipolar interaction either analytically (continuous line) or by micromagnetic simulations (small dots, dashed line is a guide to the eye).

perimental points are systematically slightly below the theoretical expectation. This could be explained by the fact that the disks are slightly smaller than their nominal value (e.g., due to some oxidation at their periphery), or that the true separation between the disks is slightly larger than expected, which we have represented on the graph by the horizontal error bars. The agreement between the analytical model and the simulation is very good until s = 0.1 µm. The discrepancy for very small s is due to a significative change in the static magnetic texture. These changes are not taken into account by the analytical model. The effect of the static coupling is to produce a static magnetization along the x-direction. As shown by the simulations, this deformation enhances the strength of the dynamical coupling.

In conclusion, we have shown that f-MRFM enables a detailed investigation of the dynamical dipolar coupling between two nearby magnetic objects, owing to the possibility of the technique to study both the tuned and detuned regime on the same object. It has been applied to study the collective SW dynamics in pairs nano-disks of Fe-V, an ultra-low damping material. Several signatures of the collective behavior have been experimentally evidenced and quantitatively explained: the anti-crossing, the hybridization of the modes and the effects on the linewidth. Moreover, we have found that in order to have a frequency splitting larger than the linewidth of the modes, the edge to edge separation between our disks has to be smaller than their diameter, due to the fast decay of the magneto-dipolar interaction. We believe that our method of local characterization of the dipolar coupling will be very useful to the field of magnonics. This research work was partially supported by the French Grants VOICE ANR-09-NANO-006-01 and MARVEL ANR-2010-JCJC-0410-01.

FIG. 2

 2 FIG. 2. a) Density plot of the experimental f-MRFM spectra as a function of the displacement x of the sphere above a pair of 600 nm Fe-V disks separated by s = 200 nm. b) Predicted behavior by micromagnetic simulations. The upper mode (blue) corresponds to the anti-binding mode (A), while the lower (red) shows the binding mode (B). Insets: simulated precession profiles in each disk for modes (A) and (B) at the anti-crossing. The dashed lines would be the individual modes of each disks in the absence of dynamical coupling.

FIG. 3

 3 FIG. 3. a) Variation of the amplitude of the binding (red) and anti-binding (blue) resonances as a function of the lateral position of the probe for the two disks separated by 200 nm. The solid lines correspond to the behavior following from Eq.4 (see text). b) Linewidth of the binding mode for the same pair at the tuning position (x = 0) c) Comparison with the measurement of the linewidth above a single disk.