RELATIONSHIP BETWEEN RHEOLOGICAL PROPERTIES AND DEGREE OF KAPPA-CASEIN PROTEOLYSIS DURING RENNETING OF MILK

Simultaneous measurement of viscosity and degree of proteolysis of kap pa-casein, alpha, in skim milk at three different concentrations of re nnet and three different concentrations of casein showed that viscosit y was a function of alpha until the former reached its minimum value. Then the relation between viscosity and alpha depended on the enzyme c oncentration. This is considered to be caused by casein micelles start ing to aggregate at this point. The minimum in viscosity was found whe n alpha was between 0.6 and 0.7, indicating that casein micelles start ed aggregating at a lower degree of proteolysis than was believed earl ier. The rate of gel firming was found to depend on the concentration of added rennet even after kappa was completely proteolysed. The resul ts demonstrated that both proteolysis of kappa-casein and aggregation of casein micelles must be taken into account when modelling the renne ting reaction.