Investigation of the Colloidal Interactions at Play in Combined Acidification and Rennet of Different Heat-Treated Milks

Abstract

The properties of gels obtained by combined acidification and rennet were investigated for milks heated at different temperature-time regimes using a high temperature short time (HTST) pilot plant system. Increasing amounts of heat-induced whey protein complexes were found in the soluble phase as a function of heating time/temperature, and only in the most extensively heated milk (i.e., 85 degrees C/300 s), these complexes were in quantities comparable to those reported in previous studies. Two levels of rennet were studied, and at the gelation pH, the amount of CMP released was 11 +/- 1% and 26 +/- 5% in the low and high rennet experiments, respectively. These two levels of rennet caused profound changes in the gelation behavior and in the structure development of the network. When a small amount of rennet was used, different heating temperature-time regimes did not affect the first stage of renneting. Increasing the extent of milk heat treatment and/or the level of rennet increased the pH of gelation and the stiffness of the gels. This work is the first to compare the effect of heating (using a pilot plant setup) and amount of rennet on the destabilization and interaction of casein micelles during aggregation by combined rennet and acidification.