Interactions in Heated Skim Milk between Genetic Variants of β-Lactoglobulin and κ-Casein

Abstract

Bovine skim milk samples with different phenotypes of κ-casein (AB and BB; κ-cn) and β-lactoglobulin (AA, AB, and BB; β-lg) were heat-treated at 90 °C for different times (1-10 min). The residual 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 β-lg was recorded. The rate of heat-induced loss of native β-lg, expressed as the inverted half-life (1/t 1/2 ) of the reaction, was calculated. The reaction did not follow true first- or second-order kinetics, varying between the different genetic combinations. The highest 1/t 1/2 values were found in milk from cows homozygous for κ-cn B or β-lg B. The same was true after adjustment for differences in casein number. Both the β-lg and κ-cn genetic variants were found to significantly influence the heat-induced aggregation reaction; with β-lg having the greatest effect. Statistical analysis showed that the two loci for β-lg and κ-cn accounted for more than half of the phenotypic variance in the experimental groups.