High pressure-induced changes in ovine milk. 2. Effects on casein micelles and whey proteins

In this study, effects of high pressure (HP) on the casein micelles and whey proteins of ovine milk were examined. Treatment at 100-400 MPa for 30 min did not denature α-lactalbumin, but treatment at 600 MPa denatured ∼70% of this protein. Denaturation of β-lactoglobulin occurred >100 MPa, reaching >90% after treatment at 400 MPa; most denatured β-lactoglobulin was associated with the casein micelles. Treatment of milk at 100 or 400 MPa did not affect average casein micelle size, but treatment at 250 increased it by ∼40% whereas treatment at 600 MPa reduced it by ∼45%; the HP-induced reduction of micelle size at 600 MPa was partially reversible on subsequent storage at 5 or 20°C. As a result of HP-induced disruption of casein micelles, the L*-value of milk decreased with pressure; reduction of the L*-value was irreversible on subsequent storage at 5°C, but partially reversible at 20°C. HP treatment affected the proteins of ovine milk in a manner analogous to in bovine, buffalo and caprine milk, although some inter-species differences in the pressure at which specific effects occur are apparent.