Interactions between different genetic variants of beta-lactoglobulin and kappa-casein A during heating of skim milk
Allmere, T.; Andren, A.; Bjorck, L.
Journal of Agricultural and Food Chemistry 45(5): 1564-1569
ISSN/ISBN: 0021-8561 Accession: 008893897
Milk samples (5 mL) from cows, homozygous for kappa-casein A and either homozygous A (n = 14) or B (n = 12) or heterozygous AB (n = 14) for beta-lactoglobulin (beta-lg), were heated at 90 degree C for 0-10 min, followed by ultracentrifugation at 1000000g. The native whey proteins in the supernatant were thereafter analyzed by fast performance liquid chromatography (FPLC), and the decrease of whey proteins was recorded. The reaction orders for the heat-induced loss of beta-lg were found to be 0.53, 0.65, and 0.91 for beta-lg A, beta-lg A+B, and beta-lg B, respectively, in milk containing the A variant of kappa-casein. The rate of heat-induced loss, expressed as the half-life (t-1/2) of the reaction, was found to be 340 and 270 s for beta-lg A and B, respectively, in milk from homozygous cows. In milk from heterozygous cows (beta-lg A+B), this value was 330 s. After correction for the casein number, the t-1/2 value for beta-lg B was still notably lower than for beta-lg A. The results, therefore, showed that the concentration of beta-lg B decreased more rapidly than beta-lg A in skim milk containing kappa-casein A, probably due to differences in hydrophobicity between the genetic variants of beta-lg.