Effect of cross-linking using aldehydes on properties of glutenin-rich films

The effect of cross-linking agents glutaraldehyde (GTA), glyoxal (GLY) and formaldehyde (FA) on relevant properties of films based on a glutenin-rich fraction from commercial wheat gluten was studied. The gliadin-rich fraction was separated from glutenin-rich fraction using 70% (v/v) aqueous ethanol solution. The 70% ethanol-insoluble fraction (glutenin-rich fraction) was dispersed in 50% (v/v) aqueous ethanol at 40 °C and pH 5. GTA, GLY or FA was added in concentrations of 2, 4 and 8% (g/100 g dry protein) to the film-forming solution. Glycerol was used as plasticizer. Films were cast and dried at 23 °C and 40% RH (relative humidity) for 10 h. Mechanical and water vapour barrier properties, color, water sorption isotherms and glass transition temperature of control and cross-linked films were evaluated. Water vapour permeability values decreased by around 30% when FA, GTA or GLY were incorporated. The highest tensile strength values were obtained using FA, followed by GTA and GLY. Glass transition temperature of cross-linked films shifts to slightly higher values when cross-linking agents were used. Films treated with GTA and GLY were darker with a yellowish color. Addition of concentrations up to 2% of cross-linker did not modify the properties of the films. Water sorption behaviour of control and cross-linked films did not differ.