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 α-lactalbumin (α-la) and β-lactoglobulin (β-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 ≥ 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 ≥2 min at 400 MPa resulted in similar levels of micelle disruption, but increasing milk pH to 7.0 partially stabilised micelles against HP-induced disruption. Denaturation of α-la did not occur ≤400 MPa, whereas β-lg was denatured at pressures > 100 MPa. Denaturation of α-la and β-lg increased with increasing pressure, treatment time and temperature and milk pH. The majority of denatured β-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.