The effect of ultra high-pressure homogenization (UHPH) on rennet coagulation properties of unheated and heated fresh skimmed milk

The effect of ultra-high pressure homogenization at a pressure of 179 MPa on the renneting of milk has been studied. The homogenization has a small effect on the diameters of casein micelles, because of the loss of some of their surface κ-casein. This modification of the structure leads to a slightly decreased rennet coagulation time. Interactions between the casein micelles in homogenized and unhomogenized milk samples started at a degree of proteolysis of the κ-casein of about 65–70%, although aggregation of the micelles did not start until over 90% proteolysis. Homogenization improved the coagulation properties of heated milk only slightly; however, it was shown that the removal of stabilizing repulsions between the casein micelles in the heated milk seemed to proceed in the same way as in unheated milk. The removal of the κ-casein has the same effect in heated and unheated milk samples, and the casein micelles are destabilized; it is only in the final aggregation step that the two milks differ.