Transglutaminase cross-linked egg white protein films: Tensile properties and oxygen permeability

A methodology for preparing biodegradable films from egg white proteins was developed in this study. Film formation was based on the partial denaturation of egg white proteins by a preheating treatment at pH 10.5, followed by enzymatic polymerization of the proteins at 50 degrees C, pH 8.2, using a Ca2+-independent microbial transglutaminase. SDS-PAGE confirmed the cross-linking of protein and showed that the polymerization reaction increased with increasing preheating temperature (from 60 to 80 degrees C) before the enzyme treatment. Films plasticized with higher glycerol content possessed higher equilibrium moisture content, indicating higher film hydrophilicity. The moisture sorption isotherms were well described by the GAB equation. Tensile properties of the films were dependent on relative humidity (RH) and glycerol content. Oxygen permeabilities of the films were low under low RH conditions but increased strongly as RH increased. Films with reduced glycerol content were better oxygen barriers but were more sensitive to RH variation.