Edible films, coatings and biodegradable packagings produced from biological materials offer numerous advantages over other conventional synthetic packaging materials. Potential applications of edible films are numerous (internal moisture or solute barriers of heterogeneous foods, individual protection of food pieces, encapsulation of food additives etc ...). Advantages, types, formation and properties of edible films with examples are reviewed in detail. Biodegradable packaging, made from entirely renewable natural polymers could contribute to solving environmental pollution and creating new markets for agricultural products. Different approaches are discussed (physical mixing of starch or co-processing of more than 50% starch with synthetic polymers, thermoplastic extruded starch etc ...) two techniques, since it is inexpensive, widely available and relatively easy to handle. 1-USE OF BIOPOLYMERS IN PACKAGING 1-1-Synthetic polymer/biopolymer mixtures Synthetic polymers become more susceptible to microbial attack when biopolymers are incorporated, i.e. biodegradability of the synthetic polymer is accelerated by adding components that can be assimilated by microorganisms. Presently, the main marketed products of this type are starch-based. Other types of biopolymers such as cellulose, lipids and vegetable proteins are not widely used ans some have been investigated only GONTARD & GUILBERT: BIO-PACKAGING, IFfEC 92 3 recently (e.g. cellulose/polyurethane mixtures 95 , gluten/synthetic resin mixtures 6 , vegetable protein/vinylic compound mixtures 36 , casein or lipid/synthetic polymer mixtures 108). 1-1-1-Filled material (first generation) The first commercial "biodegradable" plastics were developed using a technique involving extrusion mixing of granular native starch (5-2 0 %) and prooxidative and auto-oxidative additives with the synthetic polymer. This technique has been marketed by several firrns: the St Lawrence Group (Canada) under the "Ecostar" trademark; Archer baniels Midland (USA) as "Polyclean"; Polychim (France) as "Ecopolym", and Amylum as "Amyplast". Starch granules are uniforrnly dispersed in the polyethylene matrix without chemical interaction. Microbial enzyme-induced biodegradation of starch reduces the mechanical properties of the material and increase the interface between the polymer and the surrounding atmosphere (oxygen, water etc ...). This stimulates profound chemical degradation (auto-oxidation) of the synthetic phase. Poor starch/polyethylene compatibility weakens the rnechanical properties of the material, thus limiting the percentage of starch that can be added. This compatibility has been enhanced by sililation (increased hydrophobicity) of the surface of starch granules. The formed film can therefore contain up to 43% starch (St-Lawrence Corn Starch Company, Canada; Spartech, USA). Biodegradability of these rnaterials is highly

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An experimental method based on the controlled chymosin-induced kappa-casein hydrolysis of milk was proposed to modify micellar reactivity. Milk samples with a degree of kappa-casein hydrolysis of 19, 35, and 51% were obtained. The physicochemical properties of partially converted casein micelles were determined. The net negative charge of casein micelles was reduced with increasing degree of kappa-casein hydrolysis and a small but significant decrease in hydrodynamic diameter and micellar hydration were noted. Dynamic low amplitude oscillatory rheology was used to monitor the rheological properties of acid milk gels (GDL) made with partially chymosin-hydrolyzed milks in comparison with those of strictly acid and rennet gels. An increase in the gelation pH value was observed with increasing the degree of kappa-casein hydrolysis. The moduli values (G' and G'') reached 2 h after the point of gel were, for all degrees of hydrolysis tested, significantly higher than those of strictly rennet and acid gels. Comparison of changes in delta G'/delta t with time indicated differences in gel formation that could be related to the increased values of G' obtained for acid gel made with chymosin-treated milk. At a given time after gelation (2 h), increasing the degree of kappa-casein hydrolysis in milk led also to an increase in the loss tangent and the serum holding capacity of acid milk gels suggesting a correlation between these two parameters.

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In this work, the efficiency of starch acetylation to reduce water sensitivity of hydrophilic materials was investigated. Starch acetate was either included in foamed starch trays and/or used to coat these trays, wheat gluten based films or paper sheets. The water sensitivity of these foamed trays (quantity and kinetics of water uptake) is shown to decrease when starch acetate content of the foam increases. The coating of the hydrophilic trays with starch triacetate is detailled. The biodegradability of the coating was also unambigously demonstrated. Whatever the nature of the foam, the coating allowed in all cases to slow down the water uptake but best results were obtained in the case of a coated foam prepared with a starch‐starch acetate blend. The coating of wheat gluten films was tested with disappointing results because of chemical incompatibility between wheat gluten and starch acetate. In the case of paper sheet coating, the efficiency in water sensitivity reduction increased with the thickness of the coating film. However, the water sensitivity of this coated paper remained higher than paper coated with polyethylene (with a similar coating thickness).

Several proteins, lipids and waxes were tested as edible coatings on sweet corn. Only zein, a natural constituent of corn, gave a continuous adhesive and stable coating with satisfactory sensory properties. After 8 days at 10 °C, the population of L. monocytogenes was 10-fold lower on coated sweet corn than on non-coated sweet corn indicating a barrier effect of zein coating. Sorbic acid was incorporated in the coating at a concentration required to inhibit L. monocytogenes growth (approximately 1 mg sorbic acid/g of sweet corn). The inhibitory concentration was the same for both coated and non-coated sweet corn. Zein coating therefore did not improve the preservative effect of sorbic acid.

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