Formation of Sterilized Edible Films Based on Caseinates: Effects of Calcium and Plasticizers

gamma-Irradiation was used to produce free-standing sterilized edible films based on caseinate. The effects of calcium ions (Ca(2+)) and two plasticizers, namely propylene glycol (PG) and triethylene glycol (TEG), were investigated, as was the effect of the irradiation on both the gel formation and mechanical properties of the resulting films. gamma-Irradiation provoked formation of bityrosine, i.e., cross-links, accounting for the increase of the puncture strength of films. The presence of PG or TEG enhanced the formation of cross-links, leading to an improved mechanical strength of films. TEG was found to interact more favorably with the caseinate than PG, being responsible for the improved film extensibility. Addition of Ca(2+) caused the formation of gels. The breaking strength of gels was directly related to the concentration of Ca(2+), while the puncture strength of films was found to be almost independent of the calcium concentration. Moreover, a high irradiation dose seemed to affect the protein structure, accounting for the decrease of the breaking strength of gels and for the depreciation of the mechanical behavior of films.