Incidence and characteristics of cell pieces on human milk fat globules.

For biochemical and nutritional purposes, milk fat globules of a species are assumed to be more or less uniform. The incidence of organelle-containing cytoplasm (crescents) on human milk fat globules was determined by fluorescence microscopy employing acridine orange. The percentage of globules with crescents in 20 predominantly morning samples from 17 donors ranged from 1 to 38% with three-quarters falling between 3 and 8%. However, analysis of morning and night samples from eight donors showed a significant nocturnal rise in the proportion of globules with crescents. Values for night samples were, on average, twice those for morning samples. Crescents deteriorate in human milk. These changes begin in the breast, with marked disintegration occurring in milk during 36-h storage at 2 degrees C. Crescents were isolated from globules by churning and separated from the released membrane by selective centrifugation. SDS-polyacrylamide gel electrophoresis showed that crescents contribute bands which render the globule protein pattern more complex. The significance of crescents in globule secretion, globule membrane preparation, infant nutrition and as a source of mammary cell components is discussed.