The Two-Stage Coagulation of Milk Proteins in the Minimum of the Heat Coagulation Time-pH Profile of Milk: Effect of Casein Micelle Size

¹ Department of Food Chemistry, University College, Cork, Ireland

Milks with casein micelles larger or smaller than control milk were prepared by differential centrifugation. The heat stability of these modified milks increased markedly throughout the pH range 6.4 to 7.1 with decreasing casein micelle size. Within the region of the minimum in the heat coagulation time-pH profile, the control milk coagulated by a two-stage process, but the modified milks, because of their narrower casein micelle size distribution, coagulated by a single-stage process at the pH of minimum stability. The content of -CN and protein hydration increased as the size of the casein micelles decreased, and the level of glycosylation of -CN and protein surface hydrophobicity increased as a function of micelle size. The effect of casein micelle size on the heat stability of milk is likely to be related to changes in the above physico-chemical properties.

Key Words: milk • heat stability • casein micelle size

Submitted on July 6, 1999
Accepted on October 6, 1999