High pressure-induced changes in the creaming properties of bovine milk

Creaming of raw whole bovine milk at refrigeration temperatures is generally regarded as an undesirable phenomenon; traditionally, creaming is prevented by homogenising the milk. The effects of high pressure (HP) processing on the creaming of raw whole bovine milk were examined in this study. HP treatment at pressures ≤250 MPa increased the rate and level of creaming, whereas treatment at ≥400 MPa reduced both of these parameters. On treatment at 200 or 600 MPa, creaming increased or decreased, respectively, with increasing treatment time. At 400 MPa, HP-induced changes in the rate and level of creaming were strongly treatment time-dependent. Treatment at 100-600 MPa for 0-60 min had little effect on milk fat globule size, whereas the viscosity of skimmed milk increased with increasing pressure and treatment time. The amount of milk protein associated with the milk fat globules was increased by HP treatment, the extent of the increase being maximal at 200 MPa. Although increased viscosity and the level of protein associated with the fat globules may partially explain the reduced rate and level of creaming, HP-induced aggregation and denaturation of agglutinins and lipoproteins are likely to have significant effects on HP-induced changes in the creaming characteristics of milk.