A rapid evaluation of chymosin and pepsin activities in bovine rennets

The two main milk-clotting enzymes in bovine rennets, chymosin and pepsin, have different milk-clotting activity. Therefore it is important to know the enzymatic composition, which is usually determined by an IDF reference method, though it requires considerable time. In this study an easier and more rapid HPLC procedure than the reference IDF method was proposed to determine the relative activities of chymosin and pepsin in a rennet preparation. By knowing the % pepsin peak area, obtained from HPLC separation, it was possible to calculate the relative pepsin activity from an experimental equation. This suggested equation (R-2 = 0,9993) was previously obtained by processing the data concerning the relative clotting activity of pepsin (n rennet samples = 82), determined by the IDF official method, and its % peak area determined by HPLC method. The proposed procedure, validated by analysing an independent test set, resulted well correlated with the official IDF method (R-2 = 0,9836) and it could be applied for routine characterisation of bovine rennets. Other interesting information about the rennet origin (calf or adult bovine) could be obtained from the HPLC chromatographic profile, as the ratio among the four bovine pepsin fractions varied according to the age of the animal.