INFLUENCE OF KAPPA-CASEIN AND BETA-LACTOGLOBULIN GENETIC-VARIANTS ON THE HEAT-STABILITY OF MILK

Heat coagulation time-pH curves at 140 degrees C were obtained for 43 blended skim milli samples from Holstein cows to determine the effects of genetic variants of kappa-casein and beta-lactoglobulin on milk heat stability. The blended milli samples were similar in terms of protein content and milk salts, but were genotypically different for kappa-casein (AA, AB) and beta-lactoglobulin (AA, AB, BB). Type A curves were obtained for all milks. Maximum heat stability was affected by the kappa-casein genotype (AB > AA, P < 0.01) but the influence of the beta-lactogloloulin genotype was only significant when the kappa-casein AA genotype was present (beta-lactoglobulin AA > BB, P < 0.0001). Minimum heat stability was significantly higher P < 0.0001) for milk genotyped kappa-casein AB:beta-lactoglobulin BB. The effects of milk genotyped kappa-casein BB on maximum and minimum heat stability were determined by analysing individual milks: kappa-casein BB:beta-lactoglobulin AB (n = 8) and reconstituted milks: kappa-casein BB:beta-lactoglobulin AA, AB and BB (n = 17). Type B curves were obtained on three occasions for individual kappa-casein BB:beta-lactoglobulin AB milk and on five occasions in the case of reconstituted milks with kappa-casein BB:beta-lactoglobulin AA, AB and BB. This suggests a relationship between the type B curve and the kappa-casein B genetic variant. Comparison of the mean values of heat stability at the pH of maximum heat stability of each individual and reconstituted milk genotype suggested that the best genotype for kappa-casein in terms of heat stability was BB.