Quantification of milk-clotting enzymes in 40 commercial bovine rennets, comparing rocket immunoelectrophoresis with an activity ratio assay

Summary The enzymes chymosin, bovine pepsin A and bovine pepsin B in 40 commercial rennets were assayed by rocket immunoelectrophoresis, using monospecific antibody preparations against the 3 enzymes. Concentrations found were chymosin, 0–1208 mg/l; bovine pepsin A, 359–3818 mg/l; bovine pepsin B, 0–320 mg/l. Bovine pepsin B was found to be a minor enzymic component in bovine rennets, representing maximally 2·9 % of the milk-clotting activity or 9·7 % of the weight of the enzymes. The sensitivity for the quantification of the 3 enzymes was 0·5–1·0 mg/l. The coefficient of variation was 3·7 %. The sum of the immunochemical data converted into milk-clotting activities was in good agreement with the directly observed milk-clotting activity, indicating that there was no immunochemical overestimation due to the presence of non-enzymic active antigens. A high correlation was found between the enzymic composition determined immunochemically and by activity ratio assay.