Relation of Heat-induced Changes in Protein-salt Constituents to Astringency in Milk Systems

Abstract

Selected milk systems were heated at varying levels and subsequently examined for astringent flavor response, as well as by high speed centrifugation, Sephadex gel filtration, polyacryl-amide gel electrophoresis, electron microscopy, and chemical analyses, to determine changes in the size, shape, and composition of protein-salt aggregate particles present. Astringency was produced by heating various skimmilk, whey, and ultrafiltrate systems. Astringency development in whey and ultrafiltrate systems was accompanied by aggregation and formation of large protein-salt and salt particles, respectively. Heating skimmilk to produce astringency resulted in the association of calcium phosphate and whey proteins with the caseinate system without noticeably altering the size, shape, or electron density of the caseinate-phosphate micelles. Although particle size is not the sole factor related to astringency, it appears that milk components associated with astringency development must attain critical colloidal dimensions, to impart the astringent response. The effective size and chemical nature of heat-altered whey protein-salt constituents and their association with the caseinate-phosphate micelles are indicated as the primary origin of astringent flavor in milk.