THE TURBIDITY OF RENNETED SKIM MILK

The turbidity of skim milk dispersions was measured in a spectrophotometer at four different wavelengths and at various dilutions. After adding rennet to milk the transmission (~exp(-turbidity)) of the samples decreases gradually. This decrease in transmission, which depends on the volume fraction of the micelles and the wavelength of the light used, is caused by the interactions between the micelles. During the renneting the interactions change from repulsive to attractive and can be characterized by the second osmotic virial coefficient. Before the rennet is added to the milk the casein micelles can be characterized as hard spheres for which B′2 = 4VHS, where VHS is the (excluded) volume of a hard sphere. Renneting causes the casein micelles to lose their colloidal stability and B′2 decreases strongly. The micelle interaction can be described by the so-called adhesive hard sphere model, also called the “sticky" sphere model. A theory is presented which quantitatively describes the changes in transmission on renneting in the initial stages. © 1993 Academic Press, Inc.