Abrisham Tanhatan Nasseri

Jean-François Thibault

Marie-Christine Ralet
email: ralet@nantes.inra.fr

Tree and Forestry Science and Biotechnology ©2008 Global Science

Keywords: gelation, polysaccharide stabilisation ADD, acid dairy drink, ADI, acceptable daily intake, AFM, atomic force microscopy, Ara, arabinose, CCAFC, codex committee

Pectin, a plant cell wall polysaccharide, is mainly used in food industries for its gelling and stabilizing properties. In industrial applications, pectin is usually widely extracted from citrus peels, and in some intances, apple pomace is also used. Lime and lemon are the preferred citrus species used in the extraction of pectin, while orange and grapefruit are used less often. In the food industry, pectin is widely employed in the production of jams and jellies, confectionary products and bakery fillings. The fine structure of pectin is affected by many parameters, such as the origin of raw material and extraction conditions. This structural variability impacts greatly on pectin functional properties. The other major use of pectin concerns the stabilization of acidified milk drinks and yogurts. With their refreshing natural taste and high nutritional value, acidified milk drinks enjoy great popularity. A large selection of different sour milk drinks, which vary according to the manufacturing process, ingredients and consistency, is available to meet the needs of every consumer. In all cases, protein flocculation and whey separation occur in the absence of stabilizers in acidified milk drinks. To prevent this behaviour and to stabilize milk drinks, citrus pectin can be added as a protecting colloid. This review presents the structure of citrus pectin and functionality, with a special emphasis on acid dairy drinks.

INTRODUCTION

Pectin is a natural constituent of all terrestrial plants. It is one of the major plant cell wall components and is probably the most complex macromolecule in nature [START_REF] Ridley | Pectins: structure, biosynthesis, and oligosagalacturonide-related signaling[END_REF][START_REF] Coenen | Structural characterization of native pectins[END_REF]. Pectin is a heterogeneous complex polysaccharide. Its composition and fine structure vary depending on the plant source and the extraction conditions applied. The fine structure of pectin deeply affects its functionality and applicability. Although most plant tissues contain pectin, only a few plant sources are currently used for the commercial pectin extraction. Commercial pectin is produced almost exclusively from citrus peel or apple pomace [START_REF] Rolin | Commercial pectin preparations[END_REF]. The major constituent of pectin consists of linear sequences of (1ĺ4)-linked Į-D-galactopyranosyluronic acid (GalA) with some of the carboxyl groups esterified with methanol [START_REF] Voragen | Pectins. In: Stephen AM (Ed) Food Polysaccharides and their Applications[END_REF]. The proportion of GalA units that is methyl-esterified is one of the key parameters that determines the functional properties of pectin [START_REF] Rolin | (Ed) Polysaccharides[END_REF][START_REF] Ralet | Enzymatically and chemically de-esterified lime pectins: characterisation, polyelectrolyte behaviour and calcium binding properties[END_REF]. Generally, commercial pectin preparations are divided into low-methoxyl (LM) (degree of methylation (DM) < 50%) and high-methoxyl (HM) (DM > 50%) pectin. The major outlet for pectin is through food applications, i.e., as a thickener and gelling agent in jams and jellies, bakery fillings, glazing, fruit and milk beverages [START_REF] Voragen | Pectins. In: Stephen AM (Ed) Food Polysaccharides and their Applications[END_REF][START_REF] May | Pectins[END_REF][START_REF] Rolin | Commercial pectin preparations[END_REF]). Recently, pectin utilization for healthcare applications -as drug delivery, gene repair and tissue repair -has offered food ingredient manufacturers as much as $ 890 million in sales to the healthcare industry (Kalomara information 2007). This review presents the structure of citrus pectin and functionality, with a special emphasis on acid dairy drinks.

CITRUS AND CITRUS PROCESSING

Citrus is the largest fruit crop worldwide. World citrus production in selected major producing countries in 2005/06 is estimated at 72.8 million MT (USDA Foreign Agriculture Service). Citrus is grown in two belts on both sides of the equator about 20 to 40 degrees of latitude. All citrus is thought to originate from the Himalayan region of south western China and northern India. Columbus brought citrus seeds to the western hemisphere in 1493 and planted them first on the island of Hispaniola, now called Haiti (FAO 2003). Citrus became commercialized in the Americas in the late 1800s. In the early to mid 1900s, the principal producing states were Florida, Texas and California, USA [START_REF] Bates | Principles and practices of smalland medium scale fruit juice processing[END_REF]FAO 2003). Following the devastating freeze in Florida in 1962; a group of Florida businessmen began to establish citrus groves, and later citrus industry, around São Paulo, Brazil (FAO 2003). In 2005/06, citrus production in Brazil exceeded 18 million tons followed by China and USA with around 15 million tons and 10 million tons, respectively (USDA Foreign Agriculture Service). In this regard around 14 million tons and 7 million tons of Brazil and USA production, respectively, went under processing last year. Presently, more than 55% of citrus production in developed countries and 22% of production in developing countries go under processing each year. About 75% of the processing belongs to citrus juice industry, 13% citrus canning industry and 7% as dried products [START_REF] Bates | Principles and practices of smalland medium scale fruit juice processing[END_REF]FAO 2003;[START_REF] Boriss | Commodity Profile: Citrus. Agricultural Issues Center[END_REF].

There is a great variety of citrus species and citrus fruits can be roughly classified as follows:

Orange-fruit types x sweet orange x bitter orange x mandarin Yellow-fruit types

x lemon x lime, limetta x grapefruit Orange is the most important citrus product in the citrus industry, followed by grapefruits, lemons and mandarins [START_REF] Schottler | Separators, decanters and process lines for citrus processing[END_REF].

ECONOMICALLY FEASIBLE BY-PRODUCTS FROM CITRUS

Worldwide, industrial citrus waste is estimated at more than 15 × 10 6 tons per year, as the amount of residue obtained from the fruits accounts for 50% of the original whole fruit mass [START_REF] Marin | By-products from different citrus processes as a source of custommized functional fibres[END_REF]. By-products (sometimes called specialty products) are those saleable products made from citrus fruits besides juice. One of the opportunities of starting a new citrus processing operation is the unique opportunity to tailor the citrus processing plant's production of specialty products to the customer's needs. This needs to be done early in the design phase so that plants can be specially designed for the production of multiple products. Over 400 specialty-products can be made from citrus, in addition to juice. Many of these products are only research realities that lack either the backing or timing to be made profitable. It is vital to make plans on how to economically dispose of the peel and other solid wastes from operations before engaging in a fruit juice operation. There are presently 6 to 12 products that have established markets [START_REF] Bates | Principles and practices of smalland medium scale fruit juice processing[END_REF]):

x Pectin

x Pectin pomace and dietary fibre x Dried citrus peel x Pulp wash x Juice sacks and whole juice vesicles

x Beverage base and clouding agents x Healthful, nutraceutical citrus beverages x Fractionated citrus oils and D-limonene

x Citrus molasses and beverage alcohol base x Flavonoids and limonin.

PECTIN STRUCTURE

Historical outline

The scientist Vauquelin discovered the existence of pectin in fruit juices some 200 years ago [START_REF] Vauquelin | Analyse du tamarin[END_REF]. At that time, however, it was not yet called by that name. The name pectin was first used in 1825, when Braconnot continued the research started by Vauquelin. He referred to the gelforming substance as "pectic acid", from the Greek word pektikos, which means congealed, or solidified. Smolenski, in 1923, was the first to describe pectin as a polymer of GalA. In 1930, Meyer and Mark discovered the chain formation of the pectin molecule and Schneider and Bock, in 1937, established the first formula of the pectin molecule (as cited by Kertesz, 1951). The work of Kertesz (1951) defined pectin as a hetero-polysaccharide containing mainly GalA residues that are partly methyl-esterified. A certain amount of neutral sugars were detected, but the manner in which they were integrated in the pectin molecule was not determined. The work of De Vries and co-workers [START_REF] De Vries | Extraction and purification of pectins from alcohol insoluble solids from ripe and unripe ap-ples[END_REF][START_REF] De Vries | Enzymic degradation of apple pectins[END_REF] was instrumental in showing the existence of the two main pectic regions: "smooth" homogalacturonic regions and "hairy" rhamnogalacturonic regions encompassing neutral sugars side chains. From then, several other pectic domains have been described. By 1965, pectin had been established in the industry essentially as a gelling agent in jams or jellies, though thereafter other application areas were identified. Presently, pectin is used in food systems as a fat substitute, dietary fibre and as stabilizer in acidified milk systems [START_REF] Ralet | Pectins[END_REF].

Chemical structure of pectic domains

The term "pectin" is somewhat misleading since it implies the existence of a single well-defined macromolecule [START_REF] Willats | Pectin: new insights into and old polymer are starting to gel[END_REF]. In fact, pectin is currently strongly believed to contain different structural elements, the amount and fine structure of each varies widely with respect to plant origin [START_REF] Schols | Complex pectins: Structure elucidation using enzymes[END_REF], between different cell types, at different stages of cellular development, and even within the thickness of a given wall (Jauneau et al. 1998;[START_REF] Willats | Pectin: cell biology and prospects for functional analysis[END_REF][START_REF] Scheller | Biosynthesis of pectin[END_REF]).

The most commonly found structural elements are: (i) homogalacturonan, (ii) xylogalacturonan, (iii) rhamnogalacturonan I backbone, (iv) rhamnogalacturonan II, (v) arabinan, (vi) arabinogalactan I, and (vii) arabinogalactan II [START_REF] Schols | The chemical structure of pectins[END_REF][START_REF] Coenen | Structural characterization of native pectins[END_REF]) (Fig. 1).

Homogalacturonan

Homogalacturonan (HG) is the simplest and most abundant pectic structural domain. It consists of a linear backbone of (1ĺ4)-linked Į-D-GalA residues [START_REF] Ridley | Pectins: structure, biosynthesis, and oligosagalacturonide-related signaling[END_REF]. The possible presence of single rhamnose (Rha) residues within HG regions was convincingly argued against by [START_REF] Zhan | Scarcity or complete lack of single rhamnose residues interspersed within the homogalacturonan regions of citus pectin[END_REF]. The minimum estimated length of this domain is ~100 GalA residues [START_REF] Thibault | Studies of the length of homogalacturonic regions in pectins by acid hydrolysis[END_REF]. For citrus, chemical as well as enzymatic approaches have led to the isolation of HG domains of narrow molar mass distribution with a degree of polymerization of 100-120 GalA residues [START_REF] Thibault | Studies of the length of homogalacturonic regions in pectins by acid hydrolysis[END_REF][START_REF] Ralet | Mapping sugar beet pectin acetylation pattern[END_REF][START_REF] Yapo | Pectins from citrus peel cell walls contain homogalacturonans homogeneous with respect to molar mass, rhamnogalacturonan I and rhamnogalacturonan II[END_REF]. GalA residues are commonly partly methyl-esterified at C-6 (Voragen et al. 1995) and, in some plant species, partly acetylesterified at O-2 or O-3 [START_REF] Ralet | Mapping sugar beet pectin acetylation pattern[END_REF](Ralet et al. , 2008a)). Both the degree of methyl-esterification (DM) (i.e. the number of methyl-esterified GalA residues for 100 total GalA residues) and degree of acetylation (DA) (i.e. the number of acetylesterified GalA residues for 100 total GalA residues) have a profound impact on functional properties. Lime pectin is particularly rich in HG, which accounts for ~80-90% of raw pectin mass [START_REF] Ralet | Extraction and characterisation of very highly methylated pectins from lemon cell walls[END_REF]Hellín et al. 2005;[START_REF] Yapo | Pectins from citrus peel cell walls contain homogalacturonans homogeneous with respect to molar mass, rhamnogalacturonan I and rhamnogalacturonan II[END_REF]. Native citrus pectin, and its constitutive HG domains, is highly methyl-esterified and lowly acetylesterified [START_REF] Ralet | Extraction and characterisation of very highly methylated pectins from lemon cell walls[END_REF][START_REF] Ros | Extraction, characterisation, and enzymatic degradation of lemon peel pectins[END_REF][START_REF] Ros | Lemon albedo cell walls contain distinct populations of pectic hairy regions[END_REF].

Xylogalacturonan

Xylogalacturonan (XGA) consists of a HG backbone with mostly single-unit substituents of ȕ-D-xylopyranose (Xyl) linked at O-3 of GalA residues. In lemon albedo pectin, the presence of very limited amounts of XGA has been reported [START_REF] Ros | Lemon albedo cell walls contain distinct populations of pectic hairy regions[END_REF].

Rhamnogalacturonan I backbone and neutral sugars side-chains

The rhamnogalacturonan I (RG-I) backbone consists of [ĺ2)-Į-L-Rhap-(1ĺ4)-Į-D-GalpA-(1ĺ] repeats (McNeill et al. 1980(McNeill et al. , 1984;;[START_REF] Albersheim | An hypothesis: the same six polysaccharides are components of the primary cell wall of all higher plants[END_REF]. RG-I domains isolated from several plant species, including citrus, were shown to be highly acetylated at O-2 and/or O-3 of GalA units (Komavilas and Mort 1989;[START_REF] Ralet | Extraction and characterisation of very highly methylated pectins from lemon cell walls[END_REF][START_REF] Schols | Occurence of pectic hairy regions in various plant cell wall materials and their degradability by rhamnogalacturonase[END_REF][START_REF] Ros | Extraction, characterisation, and enzymatic degradation of lemon peel pectins[END_REF][START_REF] Ralet | Mapping sugar beet pectin acetylation pattern[END_REF]. So far, no evidence has been published that GalA units in RG-I domains are methyl-esterified. The Rha residues of RG-I backbone are substituted, mainly at O-4, with Į-L-arabinofuranose (Ara)-and ȕ-D-galactopyranose (Gal)containing side-chains [START_REF] Voragen | Pectins. In: Stephen AM (Ed) Food Polysaccharides and their Applications[END_REF]. Lemon pectins were shown to contain arabinan structures with a central core of (1ĺ5)-linked Araf residues carrying essentially single Araf substituents at C-3 [START_REF] Ralet | Extraction and characterisation of very highly methylated pectins from lemon cell walls[END_REF][START_REF] Ros | Extraction, characterisation, and enzymatic degradation of lemon peel pectins[END_REF]. Both types of galactans: (1ĺ4)-linked type I (arabino)-galactans and (1ĺ3),(1ĺ6)-linked type II arabinogalactans were also detected [START_REF] Ralet | Extraction and characterisation of very highly methylated pectins from lemon cell walls[END_REF][START_REF] Ros | Extraction, characterisation, and enzymatic degradation of lemon peel pectins[END_REF] as well as single D-Galp-(1ĺ4) substitutions [START_REF] Ros | Extraction, characterisation, and enzymatic degradation of lemon peel pectins[END_REF][START_REF] Ros | Lemon albedo cell walls contain distinct populations of pectic hairy regions[END_REF]. Rhamnogalacturonans I was recently recovered from citrus peels pectins after extensive degradation by homogalacturonan-degrading enzymes [START_REF] Yapo | Pectins from citrus peel cell walls contain homogalacturonans homogeneous with respect to molar mass, rhamnogalacturonan I and rhamnogalacturonan II[END_REF]. Further use of side-chains-degrading enzymes allowed the recovery of a high molar mass RG-I backbone [START_REF] Yapo | Pectins from citrus peel cell walls contain homogalacturonans homogeneous with respect to molar mass, rhamnogalacturonan I and rhamnogalacturonan II[END_REF].

Rhamnogalacturonan II

Rhamnogalacturonan II (RG-II) is a highly conserved structure in the plant kingdom. It is a low molar mass (5-10 kDa) highly complex macromolecule with a short HG-like backbone substituted by four different side-chains encompassing several unusual sugar residues [START_REF] Schols | The chemical structure of pectins[END_REF]. This structural element, although present in very limited amounts, plays a key role as it is strongly believed to be involved in the cross-linking of two pectin molecules within the cell wall through a borate di-ester (Ishii et al. 1999;Ishii and Matsunaga 2001). RG-II was recently isolated from citrus peels pectin after extensive degradation by homogalacturonan-degrading enzymes [START_REF] Yapo | Pectins from citrus peel cell walls contain homogalacturonans homogeneous with respect to molar mass, rhamnogalacturonan I and rhamnogalacturonan II[END_REF].

Pectin models

Although the structure of the different pectic domains is now quite well known, the way they are connected one with another to form a macromolecular structure is still a matter of debate. Two pectic models are considered nowadays: the "smooth and hairy regions" model [START_REF] Schols | Complex pectins: Structure elucidation using enzymes[END_REF] (Fig. 2) and the "RG-I backbone" model [START_REF] Vincken | If homogalacturonan were a side chain of rhamnogalacturonan I. Implications for cell wall architecture[END_REF]) (Fig. 3). In the first one, "smooth regions" (HG) alternate with "hairy regions" (XGA and RG-I encompassing neutral sugars side chains) to form the pectin molecule backbone, RG-II being an integral part of some HG domains. In the second one, HG, XGA, arabinan and galactan would occur as side-chains of RG-I backbone, forming a "molecular brush" [START_REF] Vincken | If homogalacturonan were a side chain of rhamnogalacturonan I. Implications for cell wall architecture[END_REF], RG-II being again an integral part of some HG domains.

Macromolecular features

The macromolecular characteristics of pectin mainly include its molar mass and conformation. These are determinants of pectin industrial applications as the strength of pectin gels is positively correlated with apparent molar mass ( 2002). Pectin molar mass vary with plant source, raw material stage of ripening and extraction conditions. It should be emphasized that a large number of factors, such as charge density, neutral sugars content and solvent quality can affect pectin aggregation and molecular state in solution.

It was also shown that pectin molecules of similar molar masses may exhibit different hydrodynamic properties due to differences in DM, branching and neutral sugars content which make their solution behaviour even more complex [START_REF] Rolin | (Ed) Polysaccharides[END_REF]. Molar mass determination is still a challenge due to problems of heterogeneity and aggregation in addition to the usual broad molar mass distribution. Developments in high-performance size-exclusion chromatography coupled with laser light scattering and/or viscometric detection, led to an improvement in pectin characterization, although aggregation and poly-dispersity can disturb lightscattering data [START_REF] Ralet | Pectins[END_REF].

Pectin conformation is a matter of complexity. As the individual sugar rings are essentially rigid, the overall conformation of the chain is primarily determined by the bridge angle and the relative orientations of the component sugars as defined by the rotational angles. The linkages between monomers in HG are axial-axial, giving the polymer an intrinsic stiffness due to the severe conformational constraints imposed by this type of linkage [START_REF] Burton | Comparative flexibility, extension and conformation of some simple polysaccharide chains[END_REF]. A rather extended conformation with a persistence length of 4.5 to 13 nm was determined on isolated HG domains or HG-rich citrus pectin [START_REF] Cros | Solution conformation of pectin polysaccharides: determination of chain characteristics by small angle neutron scattering, viscometry and molecular modelling[END_REF][START_REF] Morris | Molecular flexibility of citrus pectins by combined sedimentation and viscosity analysis[END_REF]Ralet et al. 2008b). Some contradictory conclusions have been reported concerning the influence of DM on the conformation of the pectin macromolecules. Molecular modelling, nuclear magnetic resonance and small angle neutron scattering have shown that methoxyl groups have no significant influence on the flexibility of the linkages between GalA residues [START_REF] Cros | Solution conformation of a pectin fragment disaccharide using molecular modelling and nuclear magnetic resonance[END_REF][START_REF] Cros | Solution conformation of pectin polysaccharides: determination of chain characteristics by small angle neutron scattering, viscometry and molecular modelling[END_REF]. However, other studies have shown a general decrease in the hydrodynamic volume of the pectin molecules and an increase in chain stiffness with decreasing DM, with both steric and electrostatic interactions playing an important role in conformational changes [START_REF] Morris | The effect of the degree of esterification on the hydrodynamic properties of citrus pectin[END_REF]. Using another experimental approach combining intrinsic viscosity, sedimentation coefficient and weight-average molar mass determinations, the same authors recently concluded that all citrus pectin molecules tested were of similar conformation, whatever their DM [START_REF] Morris | Molecular flexibility of citrus pectins by combined sedimentation and viscosity analysis[END_REF]. Isolated RG-I domains or RG-Irich pectin appear very flexible [START_REF] Axelos | Influence of the substituents of the carboxyl groups and of the rhamnose content on the solution properties and flexibility of pectins[END_REF]Hourdet and Muller 1991;Ralet et al. 2008b). A complex set of different factors may influence the conformation of the pectin molecules and may partly explain some of the discrepancies found in literature about this subject.

INDUSTRIAL PECTIN PRODUCTION

The citrus industry produces three intermediate products (percentage values in relation to the raw product mass):

Juice/pulp 45-55% Peel 45-55% Essential oil 0.2-0.5% [START_REF] Schottler | Separators, decanters and process lines for citrus processing[END_REF] Apple pomace, that contains 15-20% pectin, and citrus peel, which contain 30-35% pectin, are currently the only raw materials of importance to the manufacture of pectin. Historically, the major part of the pectin industry developed from utilization of apples [START_REF] Rolin | Commercial pectin preparations[END_REF][START_REF] Mesbahi | A comparative study on functional properties of beet and citrus pectins in food systems[END_REF], but today, dried citrus peel is the largest source. Among the citrus, lime and lemon are preferred and orange and grapefruit are less often used. Indeed, lime and lemon yield pectin of higher specific viscosity and lower Ca 2+ sensitivity than orange and grapefruit [START_REF] Rolin | Commercial pectin preparations[END_REF].

Pectin has been manufactured from citrus peel for more than 50 years. Pectin manufacture involves leaching, acid extraction, precipitation, purification and standardization (Fig. 4).

RG

Process

Pre-treatment and extraction

Most pectin extraction in industry is done in Europe using lime peels imported from Mexico and South America. Before industrial extraction, the raw materials are generally subjected to a pre-treatment (blanching, washing, drying) to inactivate enzymes that otherwise would rapidly degrade the pectin molecules and to increase the product stability during transportation. Washing in water, in order to leach out sugars, is necessary prior to drying so as to minimize caramelisation. Washing may even be preferred when the raw material can be used without drying, because the leachable material has to be separated from the pectin at a later stage to reach a pure product. Citrus peel is extensively leached with water and this leach water has the potential for large pollution problems. Extraction of pectins from raw materials is usually performed by acid treatment (pH 1 to 3) at high temperature (50-90°C), with nitric acid for 3-12 hours [START_REF] Rolin | Commercial pectin preparations[END_REF]. The extraction conditions (pH, temperature, time) must be optimized to provide good yields of pectin that also has the desired DM (typically 55-80). Acid extraction has at least two pitfalls: (i) it may degrade pectin structure, and (ii) it does not meet environmental safety standards. Acid-extracted pectins often contain a mixture of both Ca 2+ -sensitive (CSP) and non-Ca 2+ -sensitive (NCSP) molecules. Separation, from extracted juice, of these two types of pectin by selective precipitation has been described by Glahn (1995aGlahn ( , 1995b)). Selective precipitation is achieved by a solution of water and alcohol that contains a dissolved polyvalent cation such as Ca 2+ (usually nitrate salt), which causes the CSP to gel. It is also possible to separate CSP and NCSP directly in-situ by fractional extraction at differential pH. At pH around 3, NCSP is separated and at pH 2 (typical of normal pH for pectin extraction) extracted pectin turns out to be CSP.

Extraction technology is being continually studied and extraction processes using steam injection under pressure, microwave heating, enzymatic and microbial tools have been proposed (Fishman et al. 2000(Fishman et al. , 2003(Fishman et al. , 2006;;[START_REF] Panouillé | Cellulase and protease preparations can extract pectins from various plant byproducts[END_REF]. It has been shown that flash extracted pectin from orange albedo by microwave heating under pressure exhibited increased molar mass, size and intrinsic viscosity compared to pectin extracted by conventional heating techniques (Fishman et al. 2000). Moreover, gel forming properties of orange and lime pectin prepared by rapid microwave heating were better than those of commercial citrus pectin (Fishman et al. 2003). The USA is one of the largest producers of oranges in the world and 90% of this huge production is used to manufacture juice. Adapted extraction processes could result in the growth of pectin extraction industry in the USA using source-orange-peels that now go to waste [START_REF] Walker | Process developed by researcher may yield new industry[END_REF]).

An enzyme-hydrolytic technology would be environmentally safer and potentially more effective in terms of pectin yields [START_REF] Panouillé | Cellulase and protease preparations can extract pectins from various plant byproducts[END_REF]. Analysis of the scientific and patent literature shows that a number of research centers have been conducting studies to develop a biotechnological method for pectin extraction, but these studies are of exploratory nature only and their results are still far from industrial application [START_REF] Ptichkina | Pectin extraction from pumpkin with the aid of microbial enzymes[END_REF].

Filtration and purification

The pectin raw extract is separated from the plant residue by filtration and/or centrifugation processes. The solid: liquid ratio has to be well defined for an efficient liquid/solid separation. Ratios of 1:17 for apple and 1:35 for citrus are often used. Efficient filtration requires reasonably low viscosity, but the more water added to the process, the more energy is needed to remove it. Currently, rotary drum vacuum filtration is commonly used in the industry. Insoluble filter aids, such as wood cellulose and perlite, may be used to facilitate this process. Extracts are rapidly brought to pH 3-4, whereupon the temperature is lowered to avoid pectin demethylation and depolymerisation. Weak bases, like sodium carbonate or ammonia are used to minimize ȕ-elimination reactions. The clarified extract may be passed through a column with cation-exchange resin to remove Ca 2+ ions and generate the sodium form of pectin, which is better adapted for food application. Next, the solution is concentrated to 3-4% dry material by evaporation or membrane filtration. Pectin is then precipitated by pouring the extract into an appropriate alcohol (usually iso-propanol). The precipitate obtained is pressed, washed in a fresh bath of alcohol, pressed and finally dried and milled to a desired particle size. To recover HM-pectin, an alternative to alco- hol precipitation is precipitation by adding appropriate metal salts to the extract. Pectin forms insoluble salts with, for example, Cu 2+ and Al 3+ . Removal of metal ions from the precipitated pectin is done by washing in acidified aqueous alcohol. Pectin suspended in alcohol is in a very suitable form for further modification. The LM-pectins are generally obtained by controlled acid de-esterification or by alkali deesterification. The temperature should not exceed 50°C to avoid depolymerisation reactions. This treatment can yield HM-pectin with DM values in the range of 55-75% or LMpectin in the DM range of 20-45%. Ammonia may convert methyl-esterified carboxylate groups of pectin to primary amides. This is done industrially by suspending precipitated pectin in a mixture of alcohol and water with dissolved ammonia. By choosing proper conditions with respect to ammonia concentration, pectin with various proportions of amidated, methyl-esterified and free carboxylate groups can be produced. Regulation requires that the degree of amidation (DAm) does not exceed 25% [START_REF] Voragen | Pectins. In: Stephen AM (Ed) Food Polysaccharides and their Applications[END_REF][START_REF] Rolin | (Ed) Polysaccharides[END_REF][START_REF] May | Pectins[END_REF].

Standardization

Standardization is a current industrial practice to produce pectin samples with consistent properties. Diversity of natural raw material, climatic conditions to which the plants have been exposed, ripeness and peel pre-treatment processes may lead to large differences in pectin properties and functionalities. HM-pectin is therefore diluted and standardized with sucrose, dextrose, glucose or lactose to a given gelling power defined as degree sag. The standard of 150° sag means that 1 g of pectin is able to gel 150 g of sucrose under defined conditions of pH and temperature. Due to their large application range, LM-pectins are not necessarily standardized. For pharmaceutical purposes, pectin without admixed sugar is also available from the major manufacturers [START_REF] Voragen | Pectins. In: Stephen AM (Ed) Food Polysaccharides and their Applications[END_REF][START_REF] Rolin | (Ed) Polysaccharides[END_REF][START_REF] May | Pectins[END_REF]. So, when using pectin, it is obviously important to choose a type, which has been standardized in a way that reasonably corresponds to the intended use.

World market and regulations

Pectin extraction is an intensive energy utilizing process that requires sophisticated operations and control. Tropical developing countries may have a locally owned pectin manufacturing operation, but it is typically hard pressed to compete with imported pectin unless the native operation is given governmental protection. Typically, pectin operations are co-located with large-scale juice operations that run at least 300,000 MT of fruit per year [START_REF] Bates | Principles and practices of smalland medium scale fruit juice processing[END_REF].

The pectin industry is dominated by large multinational firms, which have undergone major changes in the past five years. The world leaders include CP Kelco (owned by I.M. Huber Corporation since 2005), Danisco sugar (Denmark), Cargill (acquired Citrico and Degussa Food Ingredients) and Herbstreith and Fox (Germany) (USDA Foreign Agricultural Service 2007). Approximately 35000 tons of pectin are produced and used each year in the world [START_REF] Daniells | Pectin sourcing advances[END_REF]USDA Foreign Agricultural Service 2007;). CP Kelco has around 40% of the market (35-40% of the world market and 35-45% of European economic area (EEA) market) followed by Danisco (20-30% of the world market and 15-25% of EEA market), Degussa Food Ingredients (10-20% of the world market and 15-25% of the EEA market), Herbsteith and Fox (5-15% of the world market and 10-20 of EEA market), Cargill and Obipektin (10% of the world and EEA market, separately). The remaining 5% is held by small processors (USDA Foreign Agricultural Service 2007).

Pectin is an essential additive in many food applications, such as beverages, protein drinks, yogurts, jams, jellies and desserts. In addition to these general applications, pectin may also hold applications as a prebiotic, potential source of soluble fiber and fat replacer in functional food and nutraceutical applications. Recent in vitro tests have shown that pectin acts as a prebiotic, by preventing pathogens from binding to the intestine and increasing the growth of probiotic bacteria in the large intestine (Iisakka 2003). In regard to fiber additives, Functional Food and Nutraceuticals estimates that besides oat bran, psyllium and soya fiber, pectin will fare the best in nutraceutical application based on a combination of cost, quality, performance and versatility advantages. In addition, a physically modified version of pectin is in the market as a fat replacer. Pectin also holds medical applications for colon specific drug delivery, which may face a potential $1 billion market in the medical field (Kalorama Information 2007). The market of pectin has been estimated to be growing at a rate of 3-5% annually since 2001. The average price of HM and LM-pectins are approximately $16000 per ton since 2006 (USDA Foreign Agricultural Service 2007).

Although the FAO/WHO joint Expert Committee on Food Additives and the EU, have not established a numerical acceptable daily intake (ADI) and consider pectin as safe, some national regulations may limit the amount of pectin added in some applications. In the US, pectin is GRAS-Generally Recognized as Safe. In most food it can be used according to good manufacturing practice in the levels needed for its application quantum satis. In the International Numbering System (INS), that provides an agreed International numerical system for identifying food additives, created by the Codex Committee on Food Additives and Contaminants (CCFAC), pectin has the number 440. In Europe, it is differentiated into E440(i) for non-amidated pectin and E440(ii) for amidated one (USDA Foreign Agricultural Service 2007).

PECTIN GELLING PROPERTIES AND APPLICATIONS

In many food products, gelation of polysaccharides is critical to the formation of structures with the desired texture. On a molecular level, an aqueous gel consists of three elements:

-Junction zones where polymer molecules are joined together; -Inter-junction segments of polymers that are relatively mobile; -Water entrapped in the polymer network. The properties of pectin gels are strongly influenced by several factors. Extrinsic factors, such as pH, ionic strength, co-solute concentrations and temperature, influence the strength, texture and general viscoelastic properties of pectin gels [START_REF] Rao | Pectins: structure, functionality, and uses[END_REF]. Intrinsic variables of the pectin macromolecules, including the molar mass, sequence of sugars along the chain, DM and distribution of the methyl groups along the chain, greatly impact on gelling properties of this polymer. Among them, DM plays the most critical role [START_REF] Rolin | (Ed) Polysaccharides[END_REF][START_REF] Cardoso | Temperature dependence of the formation and melting of pectin-Ca 2+ networks: a rheological study[END_REF].

Pectin with a high degree of polymerization is more viscous in solution than otherwise comparable pectin of lower degree of polymerization. The dependence of gel strength on the molar mass is more pronounced with breaking strength method than with non-destructive test methods. It seems highly plausible that non-homogalacturonan portion kinks the molecules and prevents aligning as well as the formation of a precipitate [START_REF] Rolin | (Ed) Polysaccharides[END_REF].

Native citrus pectin is highly methylated (HM-pectin). LM pectin is generally obtained by controlled acid or alkali de-esterification but other means, namely enzymes and ammonia, can be used. Treatment of pectin with acid, alkali or microbial (Aspergillus niger, Aspergillus japonicus, Aspergillus foetidus) pectin methyl esterase (PME) leads to pectin with a random distribution of free carboxyl group, whereas the action of alkaline PMEs from higher plants (tomato, orange, alfalfa, apple) and from fungi (Trichoderma reesei) results in a blockwise arrangement of carboxyl groups on the pectin molecule (Kohn et al. 1983;[START_REF] Thibault | Interactions of mono-and divalent counterions with alkali-and enzyme-deesterified pectins in salt-free solutions[END_REF][START_REF] Denes | Different action patterns of pectin methyl-esterase at pH 7.0 and 4.5[END_REF]. The distribution pattern of free and esterified carboxyl groups has a profound effect on gelling properties [START_REF] Ralet | Enzymatically and chemically de-esterified lime pectins: characterisation, polyelectrolyte behaviour and calcium binding properties[END_REF]. A random distribution of methyl esters gives a low Ca 2+ sensivity, while a blockwise distribution generates a local charge concentration, which may hold Ca 2+ ions in place in gel structure. CSP can gel in the presence of Ca 2+ ions without sugars and are therefore useful for low-fat or sugarless, acidic food stuff formulations (Joye and Luzio 2000). Several methods, such as conductimetry and NMR, allow the determination, to a certain extent, of the distribution of methylesters along HG domains (Kohn et al. 1983;[START_REF] Thibault | Interactions of mono-and divalent counterions with alkali-and enzyme-deesterified pectins in salt-free solutions[END_REF]Grasladen et al. 1988). More recently, an enzymatic method was developed [START_REF] Daas | Analysis of partially methyl-esterified galacturonic acid oligomers by high-performance anion-exchange chromatography and matrix-assisted laser desorption/ ionization time-of-flight mass spectrometry[END_REF][START_REF] Daas | Investigation of the non-esterified galacturonic acid distribution in pectin with endopolygalacturonase[END_REF][START_REF] Daas | Characterization of non-esterified galacturonic acid sequences in pectin with endopolygalacturonase[END_REF]Limberg et al. 2000aLimberg et al. , 2000b;;Daas et al. 2001aDaas et al. , 2001b)). Pure pectolytic enzymes were used and the generated oligosaccharides were identified and quantified by a combination of mass spectrometry and high-performance anion-exchange chromatography at pH 5. From their work, Daas and co-workers introduced the concept of "degree of blockiness" (DB) in pectin. The DB increases when the GalA residues are distributed in a more blockwise way over the pectin molecule.

The deesterification method using ammonia produces a different type of LM pectin in which some carboxylic group have been amidated. Amidated pectin has been claimed to have a blockwise distribution pattern of the amide groups and a random distribution of the free carboxyl groups [START_REF] Racapé | Properties of amidated pectins. II. Polyelectrolyte behavior and calcium binding of amidated pectins and amidated pectic acids[END_REF]. For amidated pectin, it is possible to identify the distribution of methyl esters and amide groups by using off-line coupled high-performance anion-exchange chromatography at pH 5 and mass spectrometry (Guillotin et al. 2006).

HM-pectin

Jam manufacture is the main user of industrially extracted pectin, utilizing the ability of HM pectin to form a gel with sugar and acid -the so-called low water-activity gels or sugar-acid-pectin gels. Such a gel is considered a threedimensional network of pectin molecules in which the solvent (water) encompassing the co-solutes (sugar 55-75% w/w, and acid pH 2.5-3.5) is immobilized, resulting in a system resisting deformation and showing a stress/strain relationship for small deformations. The high sugar concentration creates conditions of low water activity, which in turn promote chain-chain rather than chain-solvent interactions; whereas the acid lessens the negative charges on the carboxyl groups, thus diminishing electrostatic chain repulsion. The fact that sucrose can be replaced by other polyols, that less acid is necessary for pectin with higher DM and that a completely methoxylated pectin will gel without any acid, are considered as proof of these functions [START_REF] Voragen | Pectins. In: Stephen AM (Ed) Food Polysaccharides and their Applications[END_REF]. Junction zones formation is made possible through the smooth regions of pectin. To avoid turbidity, syneresis and precipitation, there must be junction-zone -terminating structural elements present in the chain, and "hairy regions" are thought to play such a role [START_REF] Ralet | Pectins[END_REF]. Gels formed under these conditions are stabilized by aggregated helices supported by hydrogen bonds and grouping of methyl-ester groups through hydrophobic interactions within a cage of water molecules. Recently, global structures of HM pectin in gels were visualized by atomic force microscopy (AFM) (Fishman et al. 2004(Fishman et al. , 2007)). Rods, segmented rods, rings, branched molecules, and dense circular areas of pectin were visible.

Many factors influence the conditions of gel formation and strength, among them DM is a key factor. DM controls the rate of gelation and the gelling temperature. In general, increasing the DM leads to a faster gelation and higher gelling temperature. Moreover, at constant pH and co-solute concentrations, the final gel strength increases with increasing DM. As the DM of HM-pectin decreases, a lower pH is required for gelation, although the apparent pk a increases due the decrease of DM [START_REF] Rao | Pectins: structure, functionality, and uses[END_REF]. DM correlates with the gel setting rate and gel texture under otherwise similar conditions, which means that very highly esterified pectin gels quicker at higher temperature than HM pectin of lower DM. Very highly methylated pectin will also form a more elastic and brittle gel texture compared to pectin of lower DM (Herbstreith and Fox KG Corporate Group 2003).

HM-pectin is also used in the confectionary industry for making fruit jellies and jelly centers, in fruit juices and fruit drink concentrates as a stabilizer and/or to provide mouthfeel. It is also used in fermented and directly acidified dairy drinks [START_REF] Ralet | Pectins[END_REF].

LM-pectin

Ionic-mediated gelation through divalent cations, of which the most relevant is Ca 2+ , is the classical mechanism of LMpectin gelation. The mechanism of Ca 2+ binding to the ionized carboxyl groups on the pectin chains is similar to the egg-box proposed for alginate. The Ca 2+ ions occupy the electronegative cavities in a two-fold buckled ribbon structure of the GalA residues [START_REF] Rao | Pectins: structure, functionality, and uses[END_REF].

Because of the electrostatic nature of the bonds, LMpectin is very sensitive to intrinsic parameters that can modify the environment of the carboxyl groups, such as the nature, distribution and amounts of substituents along the galacturonic backbone. Thus, the gel forming ability increases with decreasing DM. Furthermore, LM-pectin with a blockwise distribution of free carboxyl groups are very sensitive to low Ca 2+ levels (Kohn et al. 1983;[START_REF] Thibault | Interactions of mono-and divalent counterions with alkali-and enzyme-deesterified pectins in salt-free solutions[END_REF][START_REF] Ralet | Enzymatically and chemically de-esterified lime pectins: characterisation, polyelectrolyte behaviour and calcium binding properties[END_REF]. For LM blockwise pectin at low level of Ca 2+ , the gel structure will be less elastic, rather pasty with lower breaking strength compared to a gel prepared with an optimum level of Ca 2+ (Herbstreith and Fox KG Corporate Group 2003;[START_REF] Dixon | block sequences in pectin homogalacturonan by enzymatic fingerprinting with exo-and endo-polygalacturonase II from A. niger[END_REF]). An overdose of Ca 2+ will lead to pectin precipitation, also called pre-gelling. This is reversible only to a limited extent, even when the gel is once more heated above its setting temperature and cooled down without destruction (Herbstreith and Fox KG Corporate Group 2003). The traditional application of LM-pectin is in jams with soluble solids below 55% (lowcalorie jams, jelly preserves and conserves). This is the limit for HM-pectin. The heat reversibility of LM-pectin gels may be utilized in bakery jams and jellies for glazing purpose. LM-pectin also finds application in the production of fruit preparations for yogurt and fruit/milk desserts [START_REF] Ralet | Pectins[END_REF].

Amidated LM-pectin can gel under the same conditions as LM-pectin. It has a lower gelling temperature than nonamidated pectin of the same DE. Amidated LM-pectin accounts for the major part of today's use of LM-pectin. Compared to non-amidated LM-pectin, the gels are less prone to syneresis and their texture is easier to control due to functional saturation with Ca 2+ ions in most applications [START_REF] Rolin | Commercial pectin preparations[END_REF]. Amidated pectin needs less Ca 2+ to gel and is less prone to precipitation at high Ca 2+ levels, suggesting that its gelation cannot be fully explained by the "egg-box model". Indeed, blocks of amide groups along the chain promote association through hydrogen bonding [START_REF] Racapé | Properties of amidated pectins. II. Polyelectrolyte behavior and calcium binding of amidated pectins and amidated pectic acids[END_REF][START_REF] Alonso-Mougan | Rheological behaviour of an amide pectin[END_REF][START_REF] Rolin | Commercial pectin preparations[END_REF].

System parameters

At a pH of roughly 3.6 (depending on pectin type), around half of the carboxyl groups of pectin are dissociated. Repulsion between the charged groups contributes to solubility and decreases the tendency for gelation. At low pH, fewer charges are present and solubility declines, whereas at a high pH, more charges are present and solubility increases. If Ca 2+ salt is added, Ca 2+ ions may form bridges between molecules (LM-pectin mechanism) and this increases the viscosity or causes gelation. Protons compete with Ca 2+ especially at low pH. In the absence of Ca 2+ , the viscosity is inversely related to pH. That is why pectin of very low DM can gel at pH values below 2.5 [START_REF] Löfgren | Effects of calcium, pH and blockiness on kinetic rheological behavior and microstructure of HM pectin gels[END_REF].

In the presence of monovalent salts, such as NaCl, less Ca 2+ is needed for pectin to pass sol-gel transition points.

More Ca 2+ ions are indeed able to establish junction zones, while the charge of the polymer is increasingly screened by monovalent ions. The combined effect of pH and sugars promotes gelation at lower Ca 2+ levels. pH and co-solute effects on chain-solvent interactions counterbalance the decrease in the number of carboxyl groups available for Ca 2+ binding and chain-chain interactions are promoted [START_REF] Voragen | Pectins. In: Stephen AM (Ed) Food Polysaccharides and their Applications[END_REF].

In the pH range where gelation of HM-pectin usually occurs (~2.0-3.7), gel strength, setting temperature and setting rate increase with the reduction in pH, when other conditions, such as total solids content and ionic strength, remain unaltered. This is due to the enhancement of macromolecular interaction resulting from the reduction of the pectin charges. Generally, the upper limit of pH for HMpectin gelation is raised if, either the DM, total solid concentration or pectin concentration, increases. pH is a factor that is not so critical in the development of LM-pectin gels (2.0-6.0). However, it has a significant role in the final properties of the gels. A decrease in pH leads to different kinetics of gel formation and to a decrease in shear modulus, due to the decrease in the number of ionized carboxyl groups necessary for ionic complexation and gel formation. At a low pH, more Ca 2+ is needed to induce gelation than at a neutral pH. Compared to a salt-free solution, less Ca 2+ is necessary to form gels when the ionic strength increases. However, gels in salt-free solution are formed more rapidly, but the final modulus is lower [START_REF] Rao | Pectins: structure, functionality, and uses[END_REF]. When pH is below 3.5, there is the predominance of non-dissociated acid groups, which leads to more hydrogen binding in the gel network. This gives rise to a more rigid, non-shear-reversible gel network. When pH is above 3.5, there is a predominance of ionized acid groups, which favours Ca 2+ cross-linking, leading to the formation of a more spreadable, shear reversible gel network. With LM-pectin, as the soluble solids increase, the requirement for Ca 2+ decreases and the Ca 2+ bandwidth decreases [START_REF] Ralet | Pectins[END_REF].

The affinity of pectin for Ca 2+ increases with decreasing average DM and increasing length of unsubstituted galacturonan stretches. The affinity of HM-pectin for Ca 2+ is generally not high enough to lead to sufficient chain association for gelation to occur. Generally, increasing the concentration of sugar increases the gel strength, gelling temperature and gelling rate. The minimum concentration of sugar or polyol required for gelation depends on its ability to sufficiently stabilize hydrophobic interaction. For LM-pectin, the presence of sugar or other co-solutes is not necessary, but there is an increase in gelling temperature and gel strength and a decrease in syneresis as the total soluble solids increase [START_REF] Rao | Pectins: structure, functionality, and uses[END_REF].

ACID-DAIRY-DRINKS -A GROWTH SECTOR WITH A SIGNIFICANT POTENTIAL

Acid dairy drinks (ADD) are worldwide products existing in many variations, e.g. fruit milk drinks, yoghurt drinks, soy milk, butter-milk, whey drinks, kefir among others. These beverages can be described as an acidified protein liquid system with stability and viscosity similar to natural milk. Such drinks are usually composed of an acid dairy phase (fermented base) or a neutral base (milk, soy milk) with an acidic medium (fruit phase) [START_REF] Boulenguer | Comparison of the stabilization mechanism of acid dairy drinks (ADD) induced by pectin and soluble soybean polysaccharide (SPP)[END_REF].

According to DMI Dairy Management Inc TM (2007), drinkable yoghurt stands out as the fastest growing seller, not just in dairy, but in the food and beverage industry as a whole. China topped the list of producers with a whopping 49% year-over-year growth rate. Annual sales of drinkable yoghurt grew by 18.4% to $7.76 billion from mid-2005 to mid-2006 (DMI Dairy Management Inc TM 2007). Numerous opportunities for functional ingredients, such as Omega-3, phytosterols and probiotics in drinkable yoghurt, have made the products an attractive area for innovation.

Stabilizing properties (pectin-protein interactions at interfaces)

A substantial portion of pectin today is used for the stabilization of low-pH dairy drinks, including fermented drinks and mixture of fruit juice and milk. The drinks may be heattreated in order to increase their shelf life. Low viscosity and homogenous appearance are preferred characteristics. Casein, however, is prone to aggregation at low pH, particularly when subjected to heat treatment. Thus, in the absence of a stabilizer, high viscosity, whey exudation and sandy mouth feel are likely quality defects in these types of drinks [START_REF] Rolin | (Ed) Polysaccharides[END_REF]). In the late 1950s, it was proven that addition of HM-pectin to acidified milk drinks prevented the formation of sediment. Casein in milk, at its natural pH of approximately 6.6, is in the form of stable sub-micron particles, often called micelles [START_REF] Ye | Complexation between milk proteins and polysaccharides via electrostatic interaction: principles and applications -a review[END_REF]. At this pH, caseins are negatively charged. They are mutually repellent, which prevents precipitation. During acidification, electrostatic repulsion decreases and casein particles tend to aggregate. At the isoelectric point (pH 4.6), casein particles are uncharged and exhibit the weakest hydration. Below the isoelectric point, casein particles exhibit a net positive charge.

The detailed changes of the micelles above the isoelectric point can be summarized as followed:

x Between pH 5.8 and 5.5, the zeta potential decreases, leading the micelles to form clusters (particle size change from 180 to 1300 nm at pH 5.5).

- Below pH 5, aggregation of the casein is irreversible. (B) At pH > 3.5, pectin is negatively charged due to the presence of carboxylic functions. At pH 6.6, both polymers are negatively charged and repel each other. At pH ~ 4, pectin electrostatically stick to the positively charged areas of casein particles producing a highly hydrated coating, which prevents casein aggregation. Such pectin-stabilized particles are often depicted as "fuzzy golf balls".

-- - -+ - -- - -+ - -- - -+ - -- - -+ - -- - -+ - -- - -+ - + - - ++ + -- - ++ - + + - ++ + + - + ++ + -- - ++ + -+ - ++ - + - - ++ + -- - ++ - + + - ++ + + - + ++ + -- - ++ + -+ - ++ - -- - -+ - -- - -+ - -- - -+ - -- - -+ - -- - -+ - -- - -+ - - - - - - -- - - - - - - - - - - - - - + + - - ++ + + - - + - + + - + + + + - + ++ + - - ++ + -+ - ++ + -- - - -- - - - - - - - - - - - - - - - - - - -- - -
x Between pH 5.5 and 5, a re-organization of the different kinds of caseins occurs in the micelle by solubilization of Į and ȕ casein. Micelles are then associated in multi-strands and are no longer spherical.

x Below pH 5, Ca 2+ is completely soluble, the aggregation of casein is irreversible and a three-dimensional network is formed by the cluster of aggregated strands [START_REF] Boulenguer | Comparison of the stabilization mechanism of acid dairy drinks (ADD) induced by pectin and soluble soybean polysaccharide (SPP)[END_REF]. A mechanism of stabilization by pectin, under acidic conditions, was proposed in which the adsorption of the pectin on the casein micelle surface throughout carboxylicrich zones of HG domains is involved. The highly methyllated (uncharged) pectin segments would form entropy-rich loops that extend into the solution. These loops result in the repulsive interaction between the micelles at low pH in the same way as ț-casein chains do at milk pH (Rao and Lopes da Silva 2006) (Fig. 5). The stabilization of casein with pectin is only effective in the pH interval 3.2-4.5. By extension, pectin is not sufficiently dissociated at a pH below 3.5. It then either does not efficiently anchor or there is weak repulsion between "hairs" in an interpenetration zone. At a pH above 4.5, casein does not possess enough positively charged areas and there is no longer an attraction between pectin and casein [START_REF] Rolin | (Ed) Polysaccharides[END_REF]. In more concentrated acidified milk systems, it was suggested that stability is associated with the existence of a network of pectin-coated casein micelles, but a large fraction of pectin does not interact directly with acidified milk gel (large casein micelles). It was shown that less than 20% of the pectin added directly interacts with casein particles [START_REF] Syrbe | Polymer science concepts in dairy systems-An overview of milk protein and food hydrocolloid interaction[END_REF]. The remaining 80% is involved in a network with casein-pectin complexes, but plays no role in stabilizing the final product. This excess fraction seems however necessary to produce a stable system (Janhøj et al. 2008).

Recently, it was shown that (i) stabilization in ADD might be caused by a combination of depletion interaction between pectin coated casein micelles and a pectin network, (ii) that 50-90% of all pectin is bound to casein and (iii) that stability is not affected by the remaining non-bound fraction [START_REF] Boulenguer | Comparison of the stabilization mechanism of acid dairy drinks (ADD) induced by pectin and soluble soybean polysaccharide (SPP)[END_REF][START_REF] Tromp | On the mechanism of stabilisation of acidified milk drinks by pectin[END_REF].

Pectin dosage is a determinant factor in acidified milk drink stabilization. Too little pectin destabilizes the product compared to no pectin addition. If a series of milk drinks is prepared with different pectin additions, the viscosity first increases until a certain concentration is reached. A further increase in pectin amount causes a sharp decline in viscosity. A point of minimum viscosity is then reached, beyond which further addition of pectin causes a new increase in viscosity. The tendency for sediment formation grossly follows viscosity until the point of minimum viscosity. It is believed that the de-stabilization at low pectin dosages is because the adsorbing pectin molecules tend to wrap around casein particles when the surface is not crowded with pectin. Electrostatic repulsion is at a minimum because pectin has balanced the initial casein charge rather than increased numeric net charge. At full stabilization, only those pectin molecular areas, which interact strongly with casein, are anchored at the casein particles surface, whereas those areas, which are less strongly attached, are forced away from the surface [START_REF] Rolin | (Ed) Polysaccharides[END_REF]. Viscosity overshoot and final viscosity reduction become particularly pronounced when the casein particle size is low. It is striking that, independent of casein particle size, the maximum of low shear viscosity occurs at about half the pectin concentration at which the viscosity minimum (and product stability) is observed. This could point to bridging by weakly adsorbed polymers, expected to be the most pronounced at about 50% surface coverage. In contrast to the results at low shear rates, the limiting high-shear viscosity increased steadily with pectin concentration. This was interpreted as an increase in particle volume by the absorbed pectin layer, matching the results on the increased sediment volume after centrifugation. Pectin addition also changes the flow behaviour of ADD from shear-thinning and thixotropic to quasi-newtonian. This means that the system undergoes a transition from a flocculated state with partial surface coverage into a freeflowing state, where surface coverage is completed and particle attraction minimized. This conclusion is corroborated by microscopy and particle size analysis [START_REF] Rolin | (Ed) Polysaccharides[END_REF].

In industry, the pectin dosage required for optimum acidified milk stabilization depends on the formulation and production technology of the product. The stability of acidified milk drinks is evaluated on the basis of the viscosity, the amount of sediment after defined centrifugation and by microscopic examination of the protein particles (Herbstreith and Fox KG Corporate Group 2003).

Important parameters are:

x pH value of the drink (optimum range 3.9-4.1)

x protein content and particle size (1-2 ȝm~ smooth, 10-20 ȝm~ chalky, 40-60 ȝm~ grainy)

x fermentation conditions during yoghurt preparation (temperature, time, bacteria culture used to produce uniform-sized protein particles)

x conditions during direct acidification using juice or acid (direct acidification makes large protein particles)

x heat treatment during the production process (the more intense the heat treatment, the greater the risk of thermal agglomeration of protein particles).

x homogenization (10-20 MPa, to destroy caseinate gel)

x heat treatment of the finished products (it has adverse effect because of the weakest bound molecules dislodge from the complex)

x Addition of Ca 2+ (more Ca 2+ reacts with more pectin) [START_REF] Syrbe | Polymer science concepts in dairy systems-An overview of milk protein and food hydrocolloid interaction[END_REF][START_REF] Boulenguer | Comparison of the stabilization mechanism of acid dairy drinks (ADD) induced by pectin and soluble soybean polysaccharide (SPP)[END_REF]Herbstreith and Fox KG Corporate Group 2003;[START_REF] Lucey | Cultured dairy products: an overview of their gelation and texture properties[END_REF][START_REF] Tromp | On the mechanism of stabilisation of acidified milk drinks by pectin[END_REF][START_REF] Sedlmeyer | Effect of protein composition and homogenisation on the stability of acidified milk drinks[END_REF][START_REF] Mosteller | Drinkable yogurts and smoothies[END_REF][START_REF] Sejersen | Zeta potential of pectin-stabilized casein aggregates in acidified milk drinks[END_REF][START_REF] Ye | Complexation between milk proteins and polysaccharides via electrostatic interaction: principles and applications -a review[END_REF]Janhøj et al. 2008). Dilution drastically hampers the stabilization of ADD. In fact, except for Ca 2+ enriched drinks, water-dilution modifies the ionic strength, which induces a decrease in stability [START_REF] Ye | Complexation between milk proteins and polysaccharides via electrostatic interaction: principles and applications -a review[END_REF]. A high Ca 2+ concentration inhibits stabilization since it strongly enhances caseinate self-association [START_REF] Syrbe | Polymer science concepts in dairy systems-An overview of milk protein and food hydrocolloid interaction[END_REF]. ADD milk solid non-fat (MSNF) can vary from 1 to 8.5% in commercial application [START_REF] Boulenguer | Comparison of the stabilization mechanism of acid dairy drinks (ADD) induced by pectin and soluble soybean polysaccharide (SPP)[END_REF].

Types of pectin used for acid dairy drink (ADD) stabilization

ADDs are commonly stabilized by HM-Pectin [START_REF] Syrbe | Polymer science concepts in dairy systems-An overview of milk protein and food hydrocolloid interaction[END_REF][START_REF] Boulenguer | Comparison of the stabilization mechanism of acid dairy drinks (ADD) induced by pectin and soluble soybean polysaccharide (SPP)[END_REF]Herbstreith and Fox KG Corporate Group 2003;[START_REF] Lucey | Cultured dairy products: an overview of their gelation and texture properties[END_REF][START_REF] Tromp | On the mechanism of stabilisation of acidified milk drinks by pectin[END_REF][START_REF] Sejersen | Zeta potential of pectin-stabilized casein aggregates in acidified milk drinks[END_REF][START_REF] Ye | Complexation between milk proteins and polysaccharides via electrostatic interaction: principles and applications -a review[END_REF]Janhøj et al. 2008). LM-pectin with more numerous carboxyl groups should associate more strongly with the positively charged casein particles than HM-pectin. However, LM-pectin exhibits lower stabilization properties than HM-pectin. Tighter binding of pectin molecules could be the reason, leading to a flatter configuration and less polymeric stabilization, but without detailed information on the molar mass and the distribution of carboxyl residues, all this remains speculation [START_REF] Syrbe | Polymer science concepts in dairy systems-An overview of milk protein and food hydrocolloid interaction[END_REF]. HM-apple pectin is especially suited for this stabilization mechanism when a high viscosity ADD is assumed. If a low-viscosity end product is required, HM-citrus pectin is mainly used. Only HM-pectin within a very specific range of esterification (approx. 68-72%) is suited for the stabilization of ADDs. For optimum stabilization, pectin requires a high molar mass and defined Ca 2+ reactivity (Herbstreith and Fox KG Corporate Group 2003).

CONCLUSION

Pectin is a high value functional food ingredient widely used as a gelling agent and stabilizer. Food scientists and plant scientists therefore share a common goal to better understand the structure and functionalities of pectic polymers at the molecular level. The basic properties of pectin have been known for nearly 200 years, but recently there has been tremendous progress in our understanding of the very complex fine structure of pectic polymers and pectinolytic enzymes. This has been made possible by synergies between plant and food research and by the application of a range of state-of-the-art techniques including enzymatic fingerprinting, mass spectrometry, NMR, molecular modelling, and monoclonal antibodies. With this increased knowledge, there are increased opportunities for novel applications. Producers are beginning to develop a new generation of sophisticated designed pectins with specific functionalities. However, it will be important that these advances are carefully managed, so that pectin maintains its deserved reputation as a natural product.

Fig. 1

 1 Fig. 1 Schematic representation of the structural domains of pectin. Structures are drawn with the reducing terminus to the right. Homogalacturonan and homogalacturonan-derived domains are shown in the first column; rhamnogalacturonan I and attached neutral sugars side-chains are shown in the second column. The symbols of the building units are shown in the accompanying legend and the predominant linkages are explained in the text. Adapted from Vincken et al. (2003).

Fig. 2 Fig. 3

 23 Fig.2Schematic representation of the smooth and hairy model of pectin. In this "smooth and hairy regions" model[START_REF] Schols | Complex pectins: Structure elucidation using enzymes[END_REF] the pectic backbone consists of alternating homogalacturonan (HG) (smooth regions), xylogalacturonan and rhamnogalacturonan-I (RG-I). Rhamnogalacturonan-II (RG-II) is considered an integral part of HG domains. Arabinan (A) and arabinogalactan I and II (AG-I, AG-II) make up the "hairy" part of the macromolecule.

Fig. 4

 4 Fig. 4 Industrial pectin production.

  Fig. 5 Schematic representation of pectin stabilizing properties in acidified dairy drinks. (A)Casein in milk at its natural pH (~ 6.6) is in the form of stable sub-micron particles that are globally negatively charged. During fermentation, acidification occurs and casein particles become globally positively charged. Below pH 5, aggregation of the casein is irreversible. (B) At pH > 3.5, pectin is negatively charged due to the presence of carboxylic functions. At pH 6.6, both polymers are negatively charged and repel each other. At pH ~ 4, pectin electrostatically stick to the positively charged areas of casein particles producing a highly hydrated coating, which prevents casein aggregation. Such pectin-stabilized particles are often depicted as "fuzzy golf balls".

Fishman ML, Chau HK, Coffin DR, Hotchkiss AT (2003) A comparison of lime and orange pectin which were rapidly extracted from albedo. In: Voragen AGJ, Schols HA, Visser RGF (Eds) Advances in Pectin and Pectinase Research, Kluwer Academic Publishers, Dordrecht, NL, pp 107-122 Fishman ML, Chau HK, Hoagland PD, Ayyad K (2000) Characterization of pectin, flash extracted from orange albedo by microwave heating, under pressure. Carbohydrate Research 323, 126-138 Fishman ML, Chau HK, Hoagland PD, Hotchkiss AT (2006) Microwaveassisted extraction of lime pectin. Food Hydrocolloids 20, 1170-1177 Fishman ML, Cooke PH, Chau HK, Coffin DR, Hotchkiss AT (2007) Global structures of high methoxyl pectin from solution and in gels. Biomacromolecules 8, 573-578 Fishman ML, Cooke PH, Coffin DR (2004) Nanostructure of native pectin sugar acid gels visualized by atomic force microscopy. Biomacromolecules 5, 334-341 Food and Agricultural Organization of the United Nation (2003) Mediumterm prospects for agricultural commodities projection to the year 2010. FAO Corporate Document Repository. Available online: http://www.fao.org/ docrep/006/y5143e/y5143e00.HTM Glahn P (1995a) Composition containing dry pectinate salt-including food, cosmetic and super absorbent compositions. EP 656176-A1, June 7, 1995 (European patent) Glahn P (1995b) New composition comprising pectin has specific degree of esterification and ratio of calcium-sensitive pectin to sum of calcium-sensitive and non-calcium sensitive pectin. EP 664300-A1, July 26, 1995 (European patent) Grasladen H, Bakoy OE, Larsen B (1988) Determination of the degree of esterification and the distribution of methylated and free carboxyl groups in pectins by 1 H-N.M.R. spectroscopy. Carbohydrate Research 184, 183-191 Guillotin SE, Mey N, Ananta E, Boulenguer P, Schols HA, Voragen AGJ (2006) Chromatographic and enzymatic strategies to reveal differences between amidated pectins on molecular level. Biomacromolecules 7, 2032-2037 Hellìn P, Ralet M-C, Bonnin E, Thibault J-F (2005) Homogalacturonans from lime pectins exhibit homogeneous charge density and molar mass distributions. Carbohydrate Polymers 60, 307-317 Herbstreith and Fox KG Corporate Group (2003) The specialists for pectin. Available online: http://www.theingredients.co.uk/PDFs/specialist%20in%20pectin.pdf Hourdet D, Muller G (1991) Solution properties of pectin polysaccharides III: Molecular size of heterogeneous pectin chains. Calibration and application of SEC to pectin analysis. Carbohydrate Polymers 16, 409-432 Iisakka K (2003) Nutraceuticals and functional foods demand for ingredients. Available online: http://www.biomilling.com/pdf/NutraCos1103.pdf Ishii T, Matsunaga T (2001) Pectic polysaccharide rhamnogalacturonan II is covalently linked to homogalacturonan. Phytochemistry 57, 969-974 Ishii T, Matsunaga T, Pellerin P, O'Neill MA, Darvill AG, Albersheim P (1999) The plant cell wall polysaccharide rhamnogalacturonan II self-assembles into a covalently cross-linked dimer. The Journal of Biological Chemistry 274, 13098-13104 Janhøj T, Frost MB, Ipsen R (2008) Sensory and rheological characterization of acidified milk drinks. Food Hydrocolloids 22, 798-806 Jauneau A, Roy S, Reis D, Vian B (1998) Probes and microscopical methods for the localization of pectins in plant cells. International Journal of Plant Sciences 159, 1-13 Joye DD, Luzio GA (2000) Process for selective extraction of pectins from plant material by different pH. Carbohydrate Polymers 43, 337-342 Kalorama Information (2007) Medical industry offers food ingredient companies more than one billion reasons to think healthy. Available online: http:// www.kaloramainformation.com/about/release.asp?id=1023 Kertesz ZI (1951) The pectic substances. Interscience Publishers, New York. Kohn R, Markovic O, Machova E (1983) Deesterification mode of pectin by pectin esterase of Aspergillus foetidus, tomatoes and alfalfa. Collection of Czechoslovak Chemical Communications 48, 790-797 Komavilas P, Mort AJ (1989) The acetylation at O-3 of galacturonic acid in the rhamnose-rich portion of pectins. Carbohydrate Research 189, 261-272 Laurent MA, Boulenguer P (2003) Stabilization mechanism of acid dairy drinks (ADD) induced by pectin. Food Hydrocolloids 17, 445-454 Limberg G, Körner R, Buchholt HC, Christensen TMIE, Roepstorff P, Mikkelsen JD (2000a) Analysis of different de-esterification mechanisms for pectin by enzymatic fingerprinting using endopectin lyase and endopolygalacturonase II from A. niger. Carbohydrate Research 327, 293-307 Limberg G, Körner R, Buchholt HC, Christensen TMIE, Roepstorff P, Mikkelsen JD (2000b) Quantification of the amount of galacturonic residues


Camila Gomez

Geneviève Conejero

Veronique Cheynier

Nancy Terrier

Agnes Ageorges

Charaterization of new MYB genes potentially regulating anthocyanin synthesis in Vitis vinifera

de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.


T Cordonnier

A Caron

C Chauvin

P Dreyfus

J.-L Dupouey

C Ginisty

J.-D Mathias

F De Morogues

N Robert

X Rochel

From metaphor to action: implementing integrated and viable forest ecosystem management in landscapes

Objectives

The FORGECO project proposes to work within the framework of a comprehensive and integrative analysis of forest management from plot level up to the landscape level. This analysis is supported by a bottom-up participative approach in tandem with the development of decision-making tools. The project is rooted on knowledge and experience on forest silviculture and harvesting measures in tandem with their ecological and socio-economic effects. This expert approach serves to the construction and evaluation of intensification forest management scenarios.

Tools

In order to allow a spatio-temporal integration of the information and to support a decision-making process, the project relies on the development of a set of tools. This toolkit has the particularity to be generic enough to be applied according to different needs and requirements.

Two case-studies

The two sites selected (Northern Vercors and Orléanais Val-de-Loire) will provide a heterogeneous, but comprehensive reality of the forest situation in France, in order to develop and test the set of generic tools proposed to contribute to the replicability of the method.

Forest

  by the French National Research Agency and supported by the competitiveness cluster Alpine conifer domain. Dominated by Silver fir, Norway spruce and European beech species Atlantic domain. Dominated by Scots pine, Corsican pine, Sessile oak and Silver birch species

1

  Cemagref Grenoble, Unité EMGR ; 2 Engref Agroparistech, UMR METAFORT ; 3 INRA Avignon, Unité URFM ; 4 INRA Nancy, Unité EEF ; 5 Cemagref Nogent, Unité EFNO ; 6 Cemagref Clermont, Unité LISC ; 7 FCBA ; 8 IFN ; 9 Université Nancy 2, CERPA

	« « P Pr ro od du uc ce e m mo or re e, , p pr ro ot te ec ct t m mo or re e: : a a l la an nd ds sc ca ap pe e a ap pp pr ro oa ac ch h i in n a ag gr re ee em me en nt t w wi it th h m mu ul lt ti if fu un nc ct ti io on na al l f fo or re es st t m ma an na ag ge em me en nt t » »

Draft agreement signed in 2007 by ONF,

FPF, FNCOFOR and FNE


Magalie Catherine C Benjamin
email: catherine.benjamin@rennes.inra.fr.magalie.houee@rennes.inra.fr

Houée Bigot

Magalie Houée-Bigot

Measuring competition between non food and food demand on world grain markets: is biofuel production compatible with pressure for food production?

à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d'enseignement et de recherche français ou étrangers, des laboratoires publics ou privés.

Introduction

The flow of agricultural products between countries 1s conditioned by several factors including domestic and trade policy tools for the main competing exporters countries, and macroeconomic variables (such as real income per capita, rate of population growth, etc).

Important structural changes are occurring on world agricultural markets that will have an impact on the long term competitiveness of countries and regions. These changes include developments in biofuels production linked to policy incentives, and rapid growth in income and population numbers in some developing countries (such as lndia and China).

An important issue is to identify the factors that are going to modify the balance between the supply and demand for agricultural products in the long term. ln this paper, we will take the example of arable crops. These markets allow an interesting analysis since they are directly concemed with the evolution of biofuels. One important question is thus to measure the competition between food demand and non food demand.

The recent launch of public schemes in favor of the production of biofuels in many countries (for instance in the United States, in the European Union and in China) is likely to have a profound impact on policy on the equilibriums of agricultural markets for commodities linked to biofuels. lt is an acknowledged fact that biofucls have a positive effect in helping to reduce emissions of greenhouse gases. These plant-derived fuels represent new outlets for certain agricultural commodities. Although they are more expensive to produce than traditional fuels, there is considerable support from the authorities for the production of biofuels. However, the achievement of these goals, which represent a real breakthrough, will be no easy matter, and will require trade-offs to be made. On the basis of the sectors in place today, one vital requirement if this policy is to be effectively implemented, will be the management of competition in the food sector for the use of farmland.

The objective of this study is to evaluate the effect of these policies on the world markets.

Furthermore, we will study the impacts of these policies and the consequences of changes in some developing countries. The contribution made by this research is that it takes into account not only the price effects caused by the impact of these policies promoting biofuels but also the effects on areas created by the farmland resource constraint (limited areas of farmland are available). To achieve these aims, we use a multi-market partial equilibrium mode! representing the main countries operating on arable crop markets. From a tool which generates medium-term annual projections for world cereal and oilseed markets, assuming that agricultural policies remain unchanged. lt can also be used to assess the respective roi es of traditional operators and emerging countries on world agricultural markets.

The WEMAC mode! is also a simulation tool that can be used to simulate the effects of alternative policy scenarios on cereal and oilseed markets. These scenarios include alternative agricultural, domestic and trade policies, changes in agriculture and external conditions such macroeconomic shocks. The results of the simulation indicate the impact of these alternative scenarios on the equilibrium of world cereal and oilseed markets.

Specification details of the WEMAC mode!: The current country and commodity coverage

The whole mode! consists of a set of country or regional sub-models with linkages established across countries and commodities. The structure of each regional sub-model consists of the following behavioral equations: production (harvested area, yield), demand (food use, feed The mode! is characterized by a number of key features with respect to existing models, which should be highlighted from the start. First, the behavioral equations are estimated on the basis of historical data, rather than being calibrated. One key specificity is the econometric estimation of behavioural equations. One of the shortcomings linked to reference partial equilibrium models when forecasting changes in agricultural commodity markets is undoubtedly the "degree of subjectivity" involved in the adoption of behavioural equation parameters. These models are often called "empirical" models, meaning that the parameters either corne from a review of available literature or are calibrated on what experts have said [START_REF] Van Tongeren | Global models applied to agricultural and trade policies: a review and assessment[END_REF]. Secondly, as one aim of the WEMAC mode) is to provide quantitative evaluations of policy reforms, special attention is paid to modeling domestic and trade policy tools for the main producing countries, separating the effect of prices and that of other policy instruments. One of the major characteristics of current WEMAC modelling is that rather than being limited to an aggregate representation of the European Union as a whole, it actually provides information on each major European country, providing country-level estimates for France, Germany, Italy, Spain and the United-Kingdom.

Empirical analysis and Results of simulation

We have implemented two kinds of scenarios : the first one named "the non food demand scenario" and the second one called "the food demand scenario". ln the second scenario, we examine two points: the affect of a false appreciation of stocks in China and then the effect of a decrease of the economic growth in lndia.

Results of simulation are compared to the baseline. The baseline assumes a continuation of policies that are in place and policy changes that had been announced within existing The Argentine currency should continue to weaken in relation to the dollar, leading to more competitive exports (OECD, 2005). The leveling off (and even decrease) of maize exports from the United States would be due to two points; firstly, the increase in the utilization of cereals for livestock feed and secondly, the development of non-feed/food demand.

The world maize price is expected to rise between 2005 and 2015, as a result of the strong increase in consumption in relation to production. Y ear on year variations would be relatively low. The world maize price is expected to reach $121.95/t in 2015.

-Non food scenario

The non food scenario corresponds to the implementation of the mandate of incorporation in the United States (284 million hectolitres of biofuels in 2012). Two alternatives are studied: in the first case (variant A), we suppose constant arable crops area and in the second (variant B), we suppose an increase in arable crops area of 3 million hectares.

(insert table 1)

On the American market, the support for the biofuels would increase the production of corn of about 3% in the first case and about 5% in the case of an increase in arable crops area. The increase in corn production arises from the rise in the harvested area: +2. 7% in the variant A and +5.45% in the variant B. The corn consumption would increase of more than 8%: 8.13% in the variant A and 9.59% in the variant B. The corn consumption would increase more in the variant B than in the variant A because of the effect on domestic prices. ln fact, the growth of corn price would be lower in the variant B (see below). Impacts on corn supply and demand would send back directly on trade. Corn exports would strongly decrease -21.65% in the first alternative and -13.62% in the second alternative.

(insert table 2)

The effects on domestic prices are the same than those on world prices. The increase in corn consumption would lead to a rise in corn price ( + 15 .92% in the variant A and +9 .15% in the variant B). Soft wheat and soybean domestic prices would increase in the first case due to the The deceleration of the growth would strongly decrease the lndian corn imports, thus involving a considerable effect on the world price. The food scenario shows that a deceleration of the growth in India would involve a fall in the world price of common wheat of I 1 %.

In addition, this scenario also shows the impact of an error of measure in China. We analyse results on corn market. We suppose an appreciation of the supply of corn in China: increase of5%.

(Insert table 6) (Insert table 7)
The appreciation of the offer of corn in China, translated here by an increase in the offer of corn of 5%, would involve a reduction in the corn imports of China. Corn net imports would reach l.6 million tons in 2015 instead of 9 million tons in the baseline. Impacts on Chinese market would decrease corn world price of 5.15%.

Results of these different scenarios on the cereals world prices are surnmed up in this table.

(lnsert table 8)

In the non food scenario, cereals world prices would increase of about +5% for wheat and + 17% for corn. In the food scenario, soft wheat world price would decrease of -11 % and corn world price would decline of -5%. Effects of food scenario could be as strong as those of non food scenario.

These results of simulations show that even if the incentives to the production of biofuels have strong impacts on the world markets, changes on the assumptions of growth of emergent countries, for example, are also of great importance since the world markets of the field crops are affected as much. two points : the effect of an erroneous assessment of stocks in China and then the impact of an fall in economic growth in lndia.

We compare the results of the simulation to the baseline. The baseline assumes a continuation of policies that are in place and policy changes that had been announced within existing The nonfood scenario corresponds to the implementation of the mandate of incorporation in the United States (284 million hectolitres of biofuels in 2012). Two alternatives are studied: in the first case, we suppose a constant arable crop area and in the second, we suppose a 3 million hectare an increase in the arable crops area. On the American market, support for biofuels would increase the production of corn by about 3% in the first case and by about 5%

in the case of an increase in the arable crop area. Corn consumption would increase by more than 8% (between 8 and 10% depending on the two alternatives). Corn exports would decrease sharply by-19% in the first alternative and by -11 % in the second alternative. The effects on world markets would be a rise in the prices of corn ( + 16% in the first case and + 10% in the second), a rise in the prices of corn of 3% in the first case and a decrease of 1 % in the second case. ln the first case, increase in corn production would be the result of the increase in the corn area which would be achieved at the expense of other crops. ln the second case, the arable crop area increases and so the increase in the corn makes no difference to the wheat area.

The food scenario shows that a deceleration of the growth in India (2.25 per annum instead of 5.5%) would involve a fall in the world price of common wheat of 11 %. Indeed the deceleration of the growth would strongly decrease the Indian corn imports, thus involving a considerable effect on the world price. ln addition, this scenario also shows that an error of appreciation of the offer of corn in China, translated here by an increase in the offer of corn of 5%, would involve a reduction in the corn imports of China and a fall in the world price of corn of more than 5%.

These results of simulations show that even if the incentives to the production of biofuels have strong impacts on the world markets, changes on the assumptions of growth of emergent

  use, stocks), price linkages (prices transmission mechanism between domestic and world prices), trade flows (import and export equations). The behavioral equations are completed by a set of accounting identities to represent market balances. At the world level and for each commodity, a balanced situation between global imports and global exports is imposed; this constraint allows us to specify the world price. The country coverage includes ail the major producing and consuming countries of arable crops: Argentina, Brazil, Canada, China, European Union (EU-25), lndia, United States, Ukraine, Russia and a ' North Africa and Middle East' block. Countries which are not explicitly modeled are included in an endogenous aggregated block, 'Rest of the world. The mode! is based on econometric estimates of behavioral equations. Most of the equations in the mode! are estimated using annual data from the period 1970-2001. The data cornes from the USDA's PS&D database and EUROSTAT for the European Union. The structure of the WEMAC mode! and its characteristics are given in detail in the following text box.

  programs in early 2005 (like the Farm Act of 2002 in the United States, and the 2003 CAP reform). Thus, the baseline projections assume trade policies as agreed in the Uruguay Round Agreement on Agriculture. The baseline offers an assessment of arable crop markets covering cereals and oilseeds over the period 2005 to 2015. The mode! generates projections over a ten year period with specific assumptions conceming key macro economic variables as well as agricultural and trade policies. country with minimal trade barriers is chosen as a residual supplier and in general, the residual supplier is the United States.

  from the United States, traditionally the world's leading maize exporter, would fall over the period 2005-2015, to the benefit of Argentina. Maize exports from Argentina are expected to rise by more than 5.8 million tons between 2005 and 2015, to reach 19.5 million tons in 2015. Adjustments in market shares in favor of South American countries are linked to the assumption about the dollar-peso exchange rate.

  programs in early 2005 (like the Farm Act of 2002 in the United States, and the 2003 CAP reform). Thus, the baseline projections assume trade policies as agreed in the Uruguay Round Agreement on Agriculture. The baseline offers an assessment of arable crop markets covering cereals and oilseeds over the period 2005 to 2015.

Table l .

 l U.S. maize market, comparison EPA scenario to the baseline (results in 2015).

	(Thousand metric ton)	Baseline	Food scenario
			lndia
	Production	89266	88647
			(-0.69%)
	Domestic use	98410	92063
			(-6.45%)
	Net import	9142	3479
			(-61.94%)
	(Thousand metric ton)	Baseline	EP A scenario	EP A scenario
			Variant A	Variant B
	Harvested area	26029	26738	27449
			(+2.72%)	(+5.45%)
	Production	260720	268542	275375

Table 5 .

 5 Food scenario in lndia: effects on cereals world price (results in 2015).

	(U.S.$/t)	Baseline	Food scenario
			India
	Soft Wheat	151.95	134.69
			(-11.36%)
	Corn	121.95	120.94
			(-0.83%)
	Soybean	249.94	249.84
			(-0.04%)

Table 6 .

 6 Food scenario in China: effects on corn market in China (results in 20 15).

	(Thousand metric ton)	Baseline	Food scenario
			China
	Production	152866	160509
			(+5.00%)
	Domestic use	161491	161748
			(+0.16%)
	Net import	9035	1650
			(-81.74%)