Effect of high pressure homogenization on the milk fat globule membrane and its relation with the emulsion stability of milk

Abstract

Milk with 1.5 or 3.0% milk fat was heated at 65'C for 30 min or 85'C for 20 min and homogenized at 0, 30, 60, and 90 MPa. Cream was separated form the homogenized milk using centrifugation at 10,500 x g for 30 min and 20'C with addition of 2 8.6 g sucrose/ I 00 g milk to increase the difference in densities between the fat and serum phases. Homogenization pressure and heat treatment significantly affected the volumesurface average diameter of fat globules, which decreased with homogenization pressure and heating temperature. Emulsion stability of milk increased with increased homogenization pressure and heat treatment, but was not affected by the milk fat concentrations used. Homogenization of milk increased the milk fat surface area and plasma proteins were adsorbed at the oil-water interface. The amount of protein load per surface area (Mg/M2) increased with homogenization pressure and decreased with heat treatment. No significant differences in the composition of the proteins forming the MFGM of homogenized milk were found due to homogenization pressure or fat concentration, but significant differences were found due to heat treatment. The MFGM proteins in homogenized milk were composed by native membrane proteins, caseins and, (x-lactalbumin and P- lactoglobulin. Caseins were adsorbed preferentially over whey proteins at the low heat treatment, but at the higher heat treatment, a-lactalbumin and P-lactoglobulin was adsorbed at higher ratios. Changes in the ratios of individual casein proteins forming the MFGM in homogenized milk with respect of their ratios in unhomogenized milk suggested a rearrangement of the casein components at the oil-water interface during homogenization.