Differential Thermal Inactivation Analysis of Calf Rennets

A differential thermal inactivation method is used to determine the relative proportions of chymosin and bovine pepsin in commercial calf rennet extracts. The stability of these enzymes is investigated under various conditions of elevated pH, temperature, and ionic strength. Chymosin is thermally inactivated by a first order process and at a much slower rate than pepsin. An algorithm is presented for calculating the ratio of enzymes from three measurements of milk clotting activity. The rate constant of chymosin inactivation can also be determined. The method is rapid and suitable for testing in-process samples. It also provides accuracy comparable to the reference method, which requires dialysis of the rennet followed by separation of the proteins.