Effects of Calcium, Phosphate, and Bulk Culture Media on Milk Coagulation Properties

Monitoring enzymic milk coagulation by turbidity changes of undiluted milk is complementary to measurements of changes of curd firmness. Turbidity measurements are sensitive to initial stages of micelle aggregation and demonstrate that aggregation begins well before any visual observation of coagulation. A point is reached during aggregation in which a three dimensionally crosslinked network of casein micelles is formed, and following this, coagulation can be observed visually or rheologically. Coagulation time initially decreased upon calcium addition and reached a minimum at .05 M calcium. At high calcium (.4 M), coagulation time was severely retarded. Curd firming rate increased and reached a maximum at .01 M calcium. At higher calcium curd firmness was reduced. Turbidity after coagulation decreased on calcium addition suggesting that calcium affects extensiveness of the gel network. Addition of phosphate 30 min prior to enzyme addition also reduced coagulation time with minimum at .01 M phosphate. When bulk culture media were added, pH of the media had a greater effect on coagulation time than did added phosphates.