Morphological characteristics of Human Milk with different preservation method

Abstract

To examine effects of cold and frozen storage on human milk morphologically, human milk stored in cold and frozen states was examined by light and transmission electron microscopy (TEM). Human milk collected by hand expression from the same person was stored at 4°C, -2°C, or -18°C for 3 hours (controls), 3 days, 6 days, or 1 month. For light microscopy examination, one drop of human milk (20 μm in size) warmed to 37°C was dropped into 2% osmium solution on a slide glass. For TEM examination, human milk was centrifuged and the yellow portion of the upper layer was collected. In control samples, lipid balls composed of lipid droplets were observed as small granules stained black with osmium. Relatively large lipid balls appeared in human milk samples stored at 4°C for 6 days and at -2°C for one month. Many lipid balls, of increased size, were observed in human milk stored frozen, regardless of the storage period. TEM revealed lipid balls in control samples to be spherical, varying in size from approximately 2 to 6 μm, and to be surrounded by lipid droplets and limiting membranes enclosing the droplets. Although lipid droplets and limiting membranes were destroyed in some lipid balls, these balls appeared to be well preserved in human milk stored at -2°C for one month. On the other hand, in human milk stored frozen, limiting membranes were destroyed and lipid droplet size was increased in most of the lipid balls.