Relationship between rheological properties and degree of kappa-casein proteolysis during renneting of milk

Simultaneous measurement of viscosity and degree of proteolysis of kappa-casein, alpha, in skim milk at three different concentrations of rennet and three different concentrations of casein showed that viscosity was a function of alpha until the former reached its minimum value. Then the relation between viscosity and alpha depended on the enzyme concentration. This is considered to be caused by casein micelles starting to aggregate at this point. The minimum in viscosity was found when alpha was between 0.6 and 0.7, indicating that casein micelles started aggregating at a lower degree of proteolysis than was believed earlier. The rate of gel firming was found to depend on the concentration of added rennet even after kappa was completely proteolysed. The results demonstrated that both proteolysis of kappa-casein and aggregation of casein micelles must be taken into account when modelling the renneting reaction.