Formation of soluble and micelle-bound protein aggregates in heated milk.

The formation of heat-induced aggregates of kappa-casein and denatured whey proteins was investigated in milk-based dairy mixtures containing casein micelles and serum proteins in different ratios. Both soluble and micelle-bound aggregates were isolated from the mixtures heated at 95 degrees C for 10 min, using size exclusion chromatography. Quantitative analysis of the protein composition of the aggregates by reverse phase high-performance liquid chromatography strongly suggested that primary aggregates of beta-lactoglobulin and alpha-lactalbumin in a 3 to 1 ratio were involved as well as kappa-casein, and alpha(s2)-casein in micellar aggregates.

Role of the soluble and micelle-bound heat-induced protein aggregates on network formation in acid skim milk gels.

Gel formation was monitored by low amplitude rheometry during acidification at 40 degrees C with 1.5% glucono-delta-lactone in combined milk systems containing soluble and/or micelle-bound heat-induced (95 degrees C/10 min) aggregates of denatured whey proteins and kappa-casein and in heated dairy mixes with varying micellar casein/whey protein ratio (CN/WP). Both soluble and micelle-bound aggregates increased gelation pH and gel strength.

Covalent Modification of Emulsified beta-Casein Resulting from Lipid Peroxidation.

Competitive displacement of adsorbed protein from emulsion droplets by the surfactant Tween 20 has been used to determine the influence of the oil phase and aging on the behavior of beta-casein, the displaced protein being analyzed by reverse-phase high performance liquid chromatography HPLC. Unlike soluble beta-casein or the protein displaced from tetradecane droplets where aging had no effect on the appearance of the HPLC profile, the protein displaced from a soya oil emulsion interface was observed to change. As the soya oil emulsion aged, the retention time of the protein decreased.