Effect of pH on heat-induced casein-whey protein interactions: A comparison between caprine milk and bovine milk

Abstract

Skim caprine and bovine milk, adjusted to pH 6.5-7.1 were heated at 90 degrees C for 10 min. The distribution of caseins, alpha-lactalbumin (alpha-LA) and beta-lactoglobulin (beta-LG) between micellar and serum phases of both types of milk were determined. Depending on milk pH, the involvement of kappa-casein (kappa-CN) ranged from similar to 8 to 52% and from similar to 65 to 70% of total kappa-CN in bovine and caprine milk, respectively. alpha(S2)-Casein and beta-casein were only a part of micelle-bound complexes at all pH values in caprine milk. Denatured bovine beta-LG and alpha-LA were involved in both soluble and micelle-bound heat-induced protein complexes. Conversely, denatured caprine beta-LG was mainly associated with casein micelles (98-86% at pH 6.5-7.1) and was found in soluble complexes at higher pH (6-12% at pH 6.9-7.1). All denatured caprine alpha-LA was micelle-bound at all pH values. This knowledge could be very useful for understanding, controlling and modification of technological-functional properties of caprine milk.