High-pressure-induced changes in the rennet coagulation properties of bovine milk

The mechanism of high-pressure (HP)-induced changes in rennet coagulation properties of milk, particularly the role of whey protein-casein micelle associations, was studied. Treatment at 100 or 250 MPa reduced the rennet coagulation time (RCT) of raw skimmed bovine milk, compared with untreated milk. Treatment at 400 MPa had little effect, but at 600 MPa, RCT increased considerably. HP-induced increases in RCT did not occur in serum protein-free milk or milk treated with the sulphydryl-oxidising agent KIO3, which prevents association of denatured β-lactoglobulin with casein micelles. Treatment at 5 or 10 °C at 250-600 MPa resulted in shorter RCT than treatment at 20 °C. In milk without KIO3, coagulum strength was highest after treatment at 250 or 400 MPa, whereas in milk with KIO3 it was highest after treatment at 400 MPa. These results indicate the significance of HP-induced association of whey proteins with casein micelles for rennet coagulation properties of milk.