Edible films o r coatings have provided an interesting and often essential complementary means f o r controlling the quality and stability of numerous food products. There are many potential uses of edible films (e.g. wrapping various products, individual protection o f dried fruits, meat and fish, control of internal moisture transfer in pizzas, pies, etc.) which are based on t h e films properties (e.g. organoleptic, mechanical, gas and solute barrier). Polysaccharide (cellulose, starch, dextrin, vegetable and other gums, etc) and protein (gelatin, gluten, casein, etc) based films have suitable mechanical and organoleptic properties, while wax (beeswax, carnauba wax, etc) and lipid or lipid derivative films have enhanced water vapour barrier properties. The film-forming technology, solvent characteristics, plasticizing agents, temperature effects, solvent evaporation rate, coating operation and usage conditions o f the film (relative humidity, temperature) can also substantially modify the ultimate properties o f the film.

Cereal Chem. 75(1):1-9Advantages, types, formation, and properties of agricultural packaging materials based on proteins, with examples, are reviewed in detail. Proteins have long and empirically been used to make biodegradable, renewable, and edible packaging materials. Numerous cereal and vegetable proteins (such as corn zein, wheat gluten, and soy proteins) and animal proteins (such as milk proteins, collagen, gelatin, keratin, and myofibrillar proteins) are commonly used to form agricultural packaging materials. Two technological processes have been investigated to make materials based on proteins: the "wet (or solvent) process" based on dispersion or solubilization of proteins in a solvent medium, and the "dry process" based on the thermoplastic properties of proteins under low water content conditions. The macroscopic properties (including solubility in water, mechanical properties, and barrier properties) of agricultural packaging materials based on proteins are dependent mainly on the structure of the macromolecular three-dimensional network and on interactions between proteins, plasticizers, and cross-linking agents.

Biopackaging materials based on fish myofibrillar proteins have been developed. The effects of protein concentration, pH, temperature and storage time before casting on the apparent viscosity of the film forming solution (FFS) were evaluated using experimental design methodology. The first objective was to determine a feasible experimental range for film-forming. The pH and protein concentration had strong interactive effects on FFS viscosity. During FFS storage before casting, partial degradation of high molecular weight protein components led to decreased viscosity, allowing thin layer casting. In the experimental range for filmforming, none of the conditions affected film functional properties. Standard conditions were determined at: pH 3.0,2.Og protein/lOOg FFS, 25°C and 6 hr storage. The functional properties of the standard biopackaging were slightly better than those that determined for known protein-based films, with tensile strength close to those of low density polyethylene films.

At low relative humidity (RH), an edible wheat gluten film presents very low oxygen and carbon dioxide permeabilities [1.24 and 7.4 amol/(Pa m s), respectively, at 25 °C]. For higher than 60% RH, O2 and CO2 permeabilities increase exponentially [to 1290 and 36 700 amol/(Pa m s), respectively, at 95% RH], presumably due to the plasticizing effect of water molecules. Pectin, chitosan, pullulan, and myofibrillar protein films are also very permeable to O2 and CO2 at high RH. The selectivity ratio (CO2/O2 permeability) of all films tested at high RH was very high (from 10 to 28) as compared to conventional synthetic films (4 to 6). Keywords: Edible film; gas permeability; relative humidity