AFFINITY BETWEEN CHYMOSIN AND INDIVIDUAL CASEINS AT VARYING PH-VALUES

The primary action of rennet during cheese manufacture is to coagulate the caseins of the milk. In the process, some of the renneting enzyme s are retained in the curd and contribute to the ripening of the chees e. To study to what extent chymosin, the major renneting enzyme, was b ound to the different caseins, a defined amount of chymosin was incuba ted at varying pH (5.2-7.2) in the wells of microtitre plates coated w ith alpha(s)-, beta- or kappa-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 t he adsorption onto kappa-casein was less pH-dependent than onto alpha( s)- and beta-casein. It is suggested that interactions between hydroph obic areas of chymosin and the caseins, in addition to electrostatic f ords due to pH, are involved in the adsorption of chymosin by the case ins. (C) 1998 Elsevier Science Ltd. All rights reserved.