Transglutaminase decreases water vapor permeability and solubility of different hydrocolloid edible films

Edible film is a thin layer of edible coating which provides a barrier against mass transfer between food and its environment. As the materials used for edible film production are generally biodegradable, edible film can be used as a packaging alternative to synthetic plastics because of its minimal environment contamination. Components used for the preparation of edible films are classified into three categories: hydrocolloids (such as proteins or polysaccharides), lipids (such as fatty acids, acylglycerols or waxes) and composites (made by combining substances from the two previous categories) (Krochta, J.M. & Johnston, C.D.M. 1997. Food Technol., 51:61-74). It has been generally accepted that the hydrocolloid films provide an effective barrier to oxygen, carbon dioxide and lipids but not to water vapor. Moreover, they exhibit high water solubility depending on the hydrophilic nature of their components (Pol et al. 2002. J. Food Sci., 67, 212-217). It is well known that structure of film matrix is influenced by electrostatic, dipole-dipole, hydrophobic interactions as well as by hydrogen and covalent bonds. Hence, various experimental strategies have been carried out to decrease the water vapor permeability and solubility of hydrocolloids films, i.e. the use of particular crosslinking agents through either chemical or enzymatic reactions. Transglutaminase (TGase, E.C. 2.3.2.13) catalyzes the formation of -(-glutamyl)-lysine cross-links into proteins via an acyl transfer reaction. The -carboxamide group of glutamine acts as acyl donor and the -amino group of lysine serves as acyl acceptor to form intra/intermolecular isopeptide bonds (Zhu et al. 1995. App. Microbiol. Biotch., 44: 227-282). In the present study we report the production, in the absence or presence of TGase, of protein-polysaccharide films. Ovalbumin, soy and whey proteins, high- and low-methoxyl pectin, chitosan or fruit purees from strawberry, apricot and feijoa, were used as protein and polysaccharide sources respectively. Our results showed that films containing TGase cross-linked proteins exhibit improved water vapor barrier properties and are less soluble at different pHs compared to films obtained in the absence of TGase.