High Molecular Weight Fraction Participating in the Agglutination of Fat Globules in Cow's Milk

To elucidate the mechanism of creaming in cow's milk, the creaming ability of various experimental milk systems was investigated, using milk samples reconstituted from 2 types of cream and skim milk, which were prepared by centrifuging (5, 000rpm for 15 minutes at 4°C) or standing (for 17 hours at 4°C), respectively. The skim milk prepared by centrifuging (C-skim milk) and the cream prepared by standing (S-cream) showed a high agglutinating ability for milk fat globules. The ability of the ultrafiltrates prepared from both types of skim milk was found to be higher than that of original C-skim milk or skim milk prepared by standing (S-skim milk). The content of immunoglobulin M (IgM) in S-cream was confirmed to be higher than that in cream prepared by centrifuging and both types of the skim milk. Heating S-cream or C-skim milk remarkably reduced their creaming abilities. The high molecular weight fraction (P1 fraction) eluted near the void volume on the gel filtration of whey was suggested to accelerate agglutination of milk fat globules. The polypeptide pattern of P1 fraction showed a marked resemblance to that of milk fat globule membrane reported by several researchers. In addition, the P1 fraction, especially that obtained from S-cream, was found to contain a substance(s) that became white fluff at 5°C, disappeared on warming to 40°C for 30 minutes and reappeared by cooling.