Introduction: The fucosyloligosaccharides of human milk protect against several agents of pediatric disease. As with other glycoconjugates, milk oligosaccharides are synthesized by glycosyltransferases. We previously observed (J Nutr Biochem 6:582, 1995) variations in milk 3-fucosyltransferase activity among individuals and within individuals over the period of lactation, and speculated that these could result in differences in fucose-containing oligosaccharides of milk.

Aims: The first aim was to develop a sensitive, reliable assay for the routine identification and quantitation of human milk oligosaccharides, and the second was to compare the oligosaccharide profiles in random human milk samples from 50 women to assess the natural variation in a healthy population.

Methods: Oligosaccharides were isolated from the breastmilk samples, reduced with sodium borohydride, and the acidic and neutral oligosaccharides separated by ion exchange chromatography. The neutral oligosaccharides were then perbenzoylated, resolved by reversed-phase HPLC, and detected at 229 nm.

Results: The twelve most prominent oligosaccharide peaks were identified by coelution with authentic standards. They consisted of tri- to octasaccharides. Significant variations in oligosaccharide profiles of individual samples were seen, reflecting the known distribution of fucosyltransferase-dependent blood group types. The relative amount of 3-linked fucosyloligosaccharides in individual samples relates to the 3-fucosyltransferase activity of that sample.

Conclusions: A significant amount of heterogeneity exists in human milk oligosaccharides, some genetically based, that may affect the ability of human milk to protect breast-feeding infants from specific pathogens. Supported by HD 13021.