CHANGES IN STRUCTURE OF THE BOVINE-MILK FAT GLOBULE-MEMBRANE ON HEATING WHOLE MILK

The effects of heat-induced interactions between milk fat globule membrane components and skim milk proteins in whole milk on the structure of the membrane were examined by isopycnic sucrose density gradient centrifugation and by using Triton X-100 as a membrane probe. Skim milk components were incorporated into all the lipoprotein fractions separated by density gradient centrifugation. High density complexes, higher in density than those found in the natural milk fat globule membrane, were formed during the heat treatment. Losses of natural membrane polypeptides from the medium and low density lipoproteins were observed on heating. Heating whole milk also altered the rate of release of membrane components by detergent, with decreases in protein released and an increase in phospholipid constituents released. Studies on washed cream indicated that some of the changes in the membrane on heating whole milk occurred due to the heat treatment alone, independent of the interactions with skim milk proteins.