RECOMBINED MILK - FACTORS AFFECTING THE PROTEIN COVERAGE AND COMPOSITION OF FAT GLOBULE SURFACE-LAYERS

The effects of protein concentration, colloidal calcium phosphate (CCP ) content, homogenisation parameters and preheat treatments on the pro tein coverage and composition of fat globule surface layers in recombi ned milk were investigated. As the protein concentration (protein to f at ratio) was increased from 50 to 200 mg/mL fat, there was a marked i ncrease in the protein load. However, at concentrations above 200 mg/m L fat, the protein load showed little change. Caseins adsorbed in pref erence to whey proteins at all protein concentrations, the preference being greater at low concentrations. Decreasing the CCP content of ski m milk prior to homogenisation, which caused some disaggregation of ca sein micelles, decreased the protein load and altered the proportions of individual caseins at fat globule surface. A decrease in protein lo ad was observed as the homogenisation pressure was increased but the p roportions of adsorbed proteins were not significantly affected. Prehe ating reconstituted skim milk at temperatures above 70 degrees C, prio r to homogenisation, resulted in an increase in the proportion of beta -lactoglobulin adsorbed at the fat surface, which led to a small incre ase in the protein load. Decreasing the pH at preheating below 6.7 als o increased the proportion of adsorbed beta-lactoglobulin.