Differential Assay for Milk Coagulants in Mixtures with Porcine Pepsin

Abstract

An assay procedure is described for measuring milk-clotting activities of rennin, bovine pepsin, or microbial coagulant in mixtures with porcine pepsin. The total milk-clotting activity of a mixture is determined in reconstituted nonfat dry milk (Berridge substrate) at pH 6.3. A sample of mixture is incubated for 30min at pH 7.3 and 30C. The reaction is stopped by dilution with pH 6.3 acetate solution and then is assayed for residual milk-clotting activity in the Berridge substrate. The treatment at pH 7.3 completely destroys milk-clotting activities of veal and porcine pepsin components while the milk-clotting activities of rennin, adult bovine pepsin, or microbial coagulants are not affected under these conditions. A pepsin-free rennin is a standard. The method is applicable to a wide range of porcine pepsin concentrations.