Association of chymosin with artificial casein micelles as influenced by micelle composition and pH

The flavour of cheese develops partly due to retained milk-clotting enzymes in curd during cheese ripening. In this paper, the influence of the casein micelle composition, and the pH of the micelle solution on the amount of chymosin adsorbed onto casein micelles, are studied. After incubation of chymosin with artificial casein micelles of four compositions and at four pH values, the amounts of chymosin remaining in the supernatant were measured with an Enzyme Linked Immunosorbent Assay (ELISA) and a Milk Clotting Test (MCT). Results confirmed earlier findings, i.e. the lower the pH, the higher the adsorption of chymosin onto casein micelles. The beta/kappa-casein micelles adsorbed more chymosin than alpha(s)/kappa-casein micelles of the same ratio of individual caseins and pH value. Micelles of beta/kappa- or alpha(s)/kappa-casein of a ratio 12:1 were more influenced by pH than those of 3:2. Micelles of ratio 3:2, except at pH 5.2 for alpha(s)/kappa-casein, adsorbed more chymosin than those of ratio 12:1 at all pH values studied. (C) 1997 Elsevier Science Limited.