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Background. Human milk oligosaccharides help to protect infants against microbial toxins and pathogens. Variation in the structures or concentrations of protective oligosaccharides during lactation could result in different levels of protection.

Objective. The pattern of human milk oligosaccharides was measured over the course of lactation.

Methods. Neutral oligosaccharides from ninety samples of milk taken serially from twelve lactating individuals were perbenzoylated, resolved, and quantified by reversed-phase HPLC.

Results. Twelve compounds ranging from tri- to octasaccharides were identified. Oligosaccharides fell into either one group, typified by 2′-fucosyllactose and lacto-N-fucopentaose-I, representing Fucα1,2Gal fucosyltransferase activity, or into a second, typified by 3-fucosyllactose, lacto-N-fucopentaose-III, and lacto-N-difucohexaose-II, representing the activity of Fucα1,3/4Glc(GlcNAc) fucosyltransferase. In the majority of the oligosaccharide profiles of the milk samples, the products of 2-Fuc-T dominated early in lactation, but products of 3/4-Fuc-T increased steadily as lactation proceeded. In others the products of 3/4-Fuc-T dominated until near the end of lactation, at which time products of 2-Fuc-T became apparent.

Discussion. Structures and concentrations of oligosaccharides in human milk vary greatly between individuals and over the course of lactation for each individual. Generally the concentrations of the larger, more complex oligosaccharides are highest in the first weeks of lactation, after which they decline rapidly. Supported by HD13021.

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