Formation of free-standing sterilized edible films from irradiated caseinates

gamma-Irradiation was used to produce free-standing sterilized edible films based on milk protein, namely, sodium caseinate and calcium caseinate. The nature of the counterion and also the protein and glycerol concentrations were examined. Irradiation of a solution based on calcium caseinate produced more cross-links than a solution based on sodium caseinate. As a consequence, films based on calcium caseinate showed a better mechanical strength. Glycerol was found to play a double role in enhancing the formation of cross-links within caseinate chains, accounting for the increase of the puncture strength, and acting as a plasticizer, being responsible for the improved film extensibility and viscoelasticity. Moreover, the effect of the irradiation on the mechanical properties was strongly dependent on the glycerol/protein ratio, i.e., the formulation of the films. Films of high quality and a satisfactory mechanical behavior were generated at glycerol/protein ratios of 0.5 and 0.67.