Effect of Calcium, N-Ethylmaleimide and Casein upon Heat-Induced Whey Protein Aggregation

Abstract

Low- and high-speed centrifugation, Sephadex gel-filtration and polyacrylamide gel electrophoresis were employed to further investigate the nature and extent of protein aggregation produced by heating whey and skimmilk systems.Results indicated that protein aggregation in heated whey systems is a multi-reaction process involving a) denaturation of whey proteins through thiol-disulfide group, hydrogen and hydrophobic bond reactions; b) aggregation to form intermediate-sized protein particles which were excluded from Sephadex G-100 and G-200 gels and sedimentable at 144,000g but not sedimentable at 1,000g, primarily through thiol-disulfide group reactions; and c) gross aggregation of the above protein particles in the presence of calcium ions to sizes sufficient to be sedimentable at 1,000g.n-Ethylmaleimide prevented heat-induced, irreversible whey protein denaturation and interaction of whey proteins with casein by thiol-disulfide group reactions, but did not interfere with the ability of whole casein to stabilize the whey proteins against gross aggregation. Therefore, it is proposed that in addition to the more specific thiol-disulfide group reaction between β-lactoglobulin and κ-casein, denatured whey proteins are stabilized against heat-induced gross aggregation in skimmilk by complexing with casein micelles through calcium-dependent linkages.