Interactions between Different Genetic Variants of β-Lactoglobulin and κ-Casein A during Heating of Skim Milk

Abstract

Milk samples (5 mL) from cows, homozygous for κ-casein A and either homozygous A (n = 14) or B (n = 12) or heterozygous AB (n = 14) for β-lactoglobulin (β-lg), were heated at 90 °C for 0-10 min, followed by ultracentrifugation at 100000g. 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 β-lg were found to be 0.53, 0.65, and 0.91 for β-lg A, β-lg A+B, and β-lg B, respectively, in milk containing the A variant of κ-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 β-lg A and B, respectively, in milk from homozygous cows. In milk from heterozygous cows (β-lg A+B), this value was 330 s. After correction for the casein number, the t 1/2 value for β-lg B was still notably lower than for β-lg A. The results, therefore, showed that the concentration of β-lg B decreased more rapidly than β-lg A in skim milk containing κ-casein A, probably due to differences in hydrophobicity between the genetic variants of β-lg.