Mechanical and structural properties of milk protein edible films cross-linked by heating and gamma-irradiation

The mechanical properties of cross-linked edible films based on calcium cas einate and two type of whey proteins (commercial and isolate) were investig ated. Cross-linking of the proteins was carried out using thermal and radia tive treatments. Size-exclusion chromatography performed on the crosslinked proteins showed that gamma-irradiation increased the molecular weight of c alcium caseinate, while it changed little for the whey proteins. However, h eating of the whey protein solution induced crosslinking. For both cross-li nked proteins, the molecular weight distribution was greater than or equal to 2 x 10(3) kDa. Combined thermal and radiative treatments were applied to protein formulations with various ratios of calcium caseinate and whey pro teins. Whey protein isolate could replace up to 50% of calcium caseinate wi thout decreasing the puncture strength of the films. Films based on commerc ial whey protein and calcium caseinate were weaker than those containing wh ey protein isolate. Electron microscopy showed that the mechanical characte ristics of these films are closely related to their microstructures.