The fat globule size distribution in human milk.

The size distribution of fat globules in human colostrum and milk was measured using a conductometric method. The number-, surface- and volume-frequency functions were analyzed and various parameters related to the stability of the polydisperse fat emulsion were calculated. The shape of the distribution curves suggests the presence of sub-populations of differently sized particles. A postulated sub-population of small globules with a size frequency maximum below 1 micrometer comprises 70-90% of the number of globules but only a few percent of the fat volume. A sub-population of medium-sized globules with a size frequency maximum around 4 micrometer comprises the largest amount of the fat. A shoulder in the distribution curves around 8-12 micrometer indicates a third population of large globules. They contribute about 0.01% to the number of fat globules but represent 1-4% of the milk fat. The height but not the position of the maximum of the sub-distributions changed throughout lactation. This affected the size-related parameters such as the overall mean globule diameter. The volume/surface average diameter increased from about 1.8 micrometer in colostrum to 4.0 micrometer after 4-5 months of lactation. The range of globule size is similar in human and cow's milk and milk of some other species. Compared to cow's milk human milk contains more small fat globules, especially at the earlier stages of lactation.