Wheat gluten films obtained by compression molding

Abstract

Edible films based on plasticized wheat gluten protein were prepared by intensive mixing followed by compression molding, a thermoplastic process involving relatively high temperature and high pressure. The effects of water and glycerol, which were selected as plasticizers for the wheat gluten, as well as the processing conditions (mixing time and molding temperature) on the physical and mechanical properties of the films were evaluated. The resulting films were characterized in terms of moisture sorption, total soluble matter, water vapor permeability, dynamic mechanical and tensile properties. It was found that plasticizer type and concentration had a dominating effect on mechanical properties and WVP, while other physical properties remain almost non-affected. Moreover, the effect of the added plasticizer (glycerol) on the film properties strongly depends on natural presence of water in commercial gluten (9% as is). On the other hand, the pressing temperature affected the final properties of the films more than the mixing time because the former influences the final cross-linking degree of the protein network. Moreover, processing temperatures higher than 100 ºC led to darker films that would be discarded by consumers if they were used as food packaging.