Effect of heat-induced interaction between kappa -casein and beta -lactoglobulin on chymosin action

Koh, J.H.; Kim, Y.K.

Korean Journal of Dairy Science 16(3): 241-252


ISSN/ISBN: 0253-2980
Accession: 002602146

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Coagulation time, curd firmness and non-protein N (NPN) released by chymosin action were measured in skim milk, casein micelle, and casein micelle/ beta -lactoglobulin ( beta Lg) and kappa -casein/ beta Lg mixtures. The samples were treated with chymosin following heat treatment at 65 to 95 degrees C for 30 min with and without subsequent cooling to 4 degrees C for 48 h. In skim milk, coagulation was delayed and curd firmness and NPN release decreased with increase in heating temperature especially between 75 and 85 degrees C. Heating temperature had a similar influence on release of NPN from the casein micelle/ beta Lg and kappa -casein/ beta Lg mixtures but did not influence NPN release from casein micelle. When casein micelle/ beta Lg mixture was heated at 85 degrees C, the rate of NPN release gradually decreased during the 1st 15 min but showed little further decrease over the next 15 min; the amount of NPN released decreased with increase in the proportion of beta Lg in the mixture. Adjustment of pH from 5.8 to 6.8 after heating at 85 degrees C for 30 min increased the amount of NPN released by chymosin action from casein micelle/ beta Lg mixture.