Section 6
Chapter 5,552

Heat stability of milk role of beta lactoglobulin in the ph dependent dissociation of micellar kappa casein

Singh, H.; Fox, P.F.

Journal of Dairy Research 54(4): 509-522


ISSN/ISBN: 0022-0299
Accession: 005551668

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On heating casein micelle systems containing .beta.-lactoglobulin (.beta.-lg) at 90.degree.C for 10 min, .beta.-lg complexed with casein micelles at pH < 6.9, probably as a result of interaction with .kappa.-casein via sulphydryl-disulphide interchange, and co-sedimented with the micelles on ultracentrifugation. Complex formation with .beta.-lg appeared to prevent the dissociation of micellar .kappa.-casein on heating. However, at pH .gtoreq. 6.9, .kappa.-casein/.beta.-lg complexes dissociated from the micelles on heating, thus enhancing the release of micellar .kappa.-casein. High concentrations of .beta.-lg (.gtoreq. 0.8%) induced coagulation at pH 7.3, essentially by promoting the dissociation of micellar .kappa.-casein. It appeared that .alpha.s1-, .alpha.s2-, .beta.- and .kappa.-caseins dissociated from serum protein-free casein micelles to equal extents, but the presence of .beta.-lg specifically enhanced the dissociation of .kappa.-casein at pH values .gtoreq. 6.9. Micelle hydration increased slightly when casein micelles, were heated in the presence of .beta.-lg at pH 6.7, while at pH 7.3 .beta.-lg decreased the degree of hydration of casein micelles. Formation of a complex between .beta.-lg and .kappa.-casein appeared to stabilize the micelles in the pH range 6.5-6.7, possibly via increased micellar charge or degree of hydration or by preventing the dissociation of .kappa.-casein.

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