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Heat stability of milk: further studies on the pH-dependent dissociation of micellar κ-casein

Published online by Cambridge University Press:  01 June 2009

Harjinder Singh  and
Patrick F. Fox
Harjinder Singh
Affiliation:
Department of Dairy and Food Chemistry, University College, Cork, Irish Republic
Patrick F. Fox
Affiliation:
Department of Dairy and Food Chemistry, University College, Cork, Irish Republic
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Summary

Whey protein complexed and became co-sedimentable with casein micelles after heating milk at ≥ 90°C for 10 min at pH ≤ 6·9 while at higher pH values (7·3) whey proteins and κ-casein-rich protein dissociated from the micelles on heating. κ-Casein-deficient micelles were more sensitive to heat, Ca2+ or ethanol than whey protein-coated or native micelles and were readily coagulable by rennet. Isolated κ-casein added to skim milk before preheating (90°C for 10 min) did not associate with the micelles at pH ≥ 6·9. Sodium dodecyl sulphate increased the level of both non-sedimentable N (NSN) and N-acetylneuraminic acid (NANA) and shifted the NSN-pH and NANA-pH curves to more acidic values while cetyltrimethylammonium bromide had the opposite effect. It is suggested that the pH-dependent dissociation in micellar κ-casein, which appears to be reversible, depends on the surface charge on the micelles; at a certain negative charge, disruption of hydrophobic and electrostatic forces could result in the dissociation of κ-casein from the casein micelles.

Type
Original Articles
Information
Journal of Dairy Research , Volume 53 , Issue 2 , May 1986 , pp. 237 - 248
Copyright
Copyright © Proprietors of Journal of Dairy Research 1986

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