Effect of heat treatment on the rheology and structure of combined acid and rennet gels
This research project investigates the effect of high temperature-short time (HTST) heat treatment on the complexation of milk proteins and the subsequent effect on combined acid- and rennet-gels, including the immediately formed coagulum and the further processed dairy product, cottage cheese. Relative to previous studies on lab heated milk, the soluble complexes in HTST-heated milk were of a smaller size and altered protein composition. Heat treatment resulted in earlier aggregation of casein micelles and formation of stiffer networks. This effect was reduced upon increasing the level of rennet, presumably because of the contribution of the rennet-destabilized complexes to the formation of the intermediate network. Large deformation measurements showed that heating affected not only the hardness but also the viscoelastic properties of the curd. Cottage cheese curd produced from the extensively heated milk had high stiffness, although the inclusion of whey proteins and higher moisture content resulted in a softer texture.