About rennet properties of milk

Effects of the variability of milk on ability to rennet coagulation were studied. Titratable acidity (°T) and active acidity (pH), calcium levels in skim milk were determined. The rennet coagulation was assessed by the cup of the VNIIMC and by the time of curd appearance. The rennet, bovine pepcine and chicken pepcine we used as coagulants. Correlation between active and titratable acidities and results received with the cup of the VNIIMC was evaluated. The pH value appeared to be the most stable index (the average 6.69 and standard deviation 0,05). Maximum variations were observed in the results received with the VNIIMC cup (2,85 and 0,7 correspondingly). It was shown that activity of the rennet powder, bovine pepcine and chicken pepcine greatly depends on the concrete milk sample and is not compensated by the pH correction. For the enzymes tested natural level of calcium in milk in the range from 113 to 134 mg % (deviation is approximately by 20%) is not connected by dependence with time of rennet coagulation. Complex preparations containing rennet, bovine and chicken pepcines are more sensitive to the change of milk as compared with rennet: the relative impact of some separate components of the complex preparations can become stronger or weaker in various milks. The conclusion was made that physical-chemical indices (acidity and calcium level) do not allow foresee rennet properties of milk. It is impossible to expect standard behavior of the milk clotting enzyme preparations of varying compositions in the random samples of natural milk.

rennet coagulation, active acidity, titratable acidity, the cup of VNIIMC, rennet powder, bovine pepcine, chicken pepcine