Affinity between chymosin and individual caseins at varying pH-values

Abstract

The primary action of rennet during cheese manufacture is to coagulate the caseins of the milk. In the process, some of the renneting enzymes are retained in the curd and contribute to the ripening of the cheese. To study to what extent chymosin, the major renneting enzyme, was bound to the different caseins, a defined amount of chymosin was incubated at varying pH (5.2–7.2) in the wells of microtitre plates coated with αs-, β- or κ-casein. The amount of retained chymosin after incubation was calculated from the amount added minus the amount of free chymosin, which was measured by an ELISA method. It was found that the adsorption of chymosin increased with lowering pH and that the adsorption onto κ- casein was less pH-dependent than onto αs- and β-casein. It is suggested that interactions between hydrophobic areas of chymosin and the caseins, in addition to electrostatic forces due to pH, are involved in the adsorption of chymosin by the caseins.