Water solubility, mechanical, barrier, and thermal properties of cross-linked whey protein isolate-based films

Water solubility, thermal properties, tensile strength, percent elongation, oxygen permeability (OP), and water-vapor permeability (WVP) of cross-linked glycerol plasticized whey protein isolate films were studied to determine the effect of cross-linkers (glutaraldehyde, formaldehyde, dialdehyde starch, carbonyldiimidazole, and UV irradiation) on film properties. With the exception of UV treatment, solubility of the films decreased (P < 0.05) upon treatment of the film-forming solutions with chemical cross-linkers. Tensile strength increased (P < 0.05), whereas percent elongation was not affected by cross-linking. Chemical cross-linking increased (P < 0.05) WVP and decreased (P < 0.05) OP of the films. UV treatment had no effect on WVP and OP. With the exception of UV-treated films, both onset temperature and degradation temperatures, as determined by differential scanning calorimetry, were increased upon cross-linking.