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

The mechanical properties of cross-linked edible films based on calcium caseinate and two type of whey proteins (commercial and isolate) were investigated. Cross-linking of the proteins was carried out using thermal and radiative treatments. Size-exclusion chromatography performed on the crosslinked proteins showed that gamma-irradiation increased the molecular weight of calcium caseinate, while it changed little for the whey proteins. However, heating of the whey protein solution induced crosslinking. For both cross-linked 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 proteins. Whey protein isolate could replace up to 50% of calcium caseinate without decreasing the puncture strength of the films. Films based on commercial whey protein and calcium caseinate were weaker than those containing whey protein isolate. Electron microscopy showed that the mechanical characteristics of these films are closely related to their microstructures.