INTERACTIONS IN HEATED SKIM MILK BETWEEN GENETIC-VARIANTS OF BETA-LACTOGLOBULIN AND KAPPA-CASEIN

Bovine skim milk samples with different phenotypes of kappa-casein (AB and BB; kappa-cn) and beta-lactoglobulin (AA, AB, and BE; beta-lg) we re heat-treated at 90 degrees C for different times (1-10 min). The re sidual native whey proteins in the ultracentrifugal supernatants were determined by fast performance liquid chromatography using a MonoQ HR5 /5 column at pH 6.2, and the loss of native beta-lg was recorded. The rate of heat-induced loss of native beta-lg, expressed as the inverted half-life (1/t(1/2)) of the reaction, was calculated. The reaction di d not follow true first- or second-order kinetics, varying between the different genetic combinations. The highest 1/t(1/2) values were foun d in milk from cows homozygous for kappa-cn B or beta-lg B. The same w as true after adjustment for differences in casein number. Both the be ta-lg and kappa-cn genetic variants were found to significantly influe nce the heat-induced aggregation reaction; with beta-lg having the gre atest effect. Statistical analysis showed that the two loci for beta-l g and kappa-cn accounted for more than half of the phenotypic variance in the experimental groups.