Time-dependent crosslinking of whey protein based films during storage

Environmentally-friendly packaging based on whey protein offers the potential to replace petroleum-based oxygen barrier materials. Effective crosslinking of the whey protein is a prerequisite for this application. To quantify the effect of storage time on the post-crosslinking of whey protein isolate based films, swelling tests were conducted in order to determine the degree of swelling (DoS). In addition, the degree of crosslinking (DoC) and the crosslinking density (CLD) were calculated using existing models with new data from water vapour sorption isotherm measurements. The results showed that increasing storage time led to decreased swelling of whey protein isolate based films (p < .05) and increased DoC and CLD (p < .05). Comparison of the films on day 1 and day 21 showed that the crosslinking increased by a factor of 3 while the DoS reduced by almost half. The results of this study demonstrate that the storage time of whey protein isolated based films is a crucial factor for crosslinking.