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 he at stability. The blended milli samples were similar in terms of prote in content and milk salts, but were genotypically different for kappa- casein (AA, AB) and beta-lactoglobulin (AA, AB, BB). Type A curves wer e obtained for all milks. Maximum heat stability was affected by the k appa-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). Minimu m heat stability was significantly higher P < 0.0001) for milk genotyp ed kappa-casein AB:beta-lactoglobulin BB. The effects of milk genotype d kappa-casein BB on maximum and minimum heat stability were determine d by analysing individual milks: kappa-casein BB:beta-lactoglobulin AB (n = 8) and reconstituted milks: kappa-casein BB:beta-lactoglobulin A A, 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 til e type B curve and the kappa-casein B genetic variant. Comparison of t he mean values of heat stability at the pH of maximum heat stability o f each individual and reconstituted milk genotype suggested that the b est genotype for kappa-casein in terms of heat stability was BB.