High pressure treatment of bovine milk: effects on casein micelles and whey proteins

Effects of high pressure (HP) on average casein micelle size and denaturation of (alpha)lactalbumin ((alpha)-la) and (beta)-lactoglobulin ((beta)-lg) in raw skim bovine milk were studied over a range of conditions. Micelle size was not influenced by treatment at pressures <200 MPa, but treatment at 250 MPa increased micelle size by ~25%, while treatment at [gt-or-equal, slanted]300 MPa irreversibly reduced it to ~50% of that in untreated milk. The increase in micelle size after treatment at 250 MPa was greater with increasing treatment time and temperature and milk pH. Treatment times [gt-or-equal, slanted]2 min at 400 MPa resulted in similar levels of micelle disruption, but increasing milk pH to 7u0 partially stabilised micelles against HP-induced disruption. Denaturation of (alpha)-la did not occur [less-than-or-eq, slant]400 MPa, whereas (beta)-lg was denatured at pressures >100 MPa. Denaturation of (alpha)-la and (beta)-lg increased with increasing pressure, treatment time and temperature and milk pH. The majority of denatured (beta)-lg was apparently associated with casein micelles. These effects of HP on casein micelles and whey proteins in milk may have significant implications for properties of products made from HP-treated milk.