A method for isolation of milk fat globules

The traditional procedure for isolating milk fat globules involves repeated cycles of centrifuging to obtain globules and redispersion of them in fresh buffer to eliminate other milk components. We have evaluated a simpler, less manipulative method whereby globules are centrifuged out of the milk and through an overlying buffer layer. Human milk samples ranging from 0.1 to 35 ml were centrifuged at 1500 X g for 20 min after deposition under a suitable quantity of buffer. This yielded purified globules, in less time, which could be dispersed more satisfactorily than those by the traditional procedure. Protein, phospholipid and cholesterol contents of globules by the two methods were quite similar. A lower protein content (10.4 vs 13.2 mg/g of lipid) was characteristic of globules prepared by the multiple wash method. However, large differences could not be seen in gel electrophoresis patterns of the proteins. By using plastic centrifuge tubes, tube freezing and cleavage just below the globule layer enables clean separation of globule and nonglobule phases for analysis of milk component distributions. Macro (5 to 35 ml of sample) and micro (200 microliter or less) versions of the method are described. Limited trials showed that the method can be applied satisfactorily to cow's and goat's milks, but for highly pure globules a deeper buffer column than that used with human milk is required because of their much higher casein content.