Human milk contains a high concentration of diverse soluble oligosaccharides, carbohydrate
polymers formed from a small number of monosaccharides. Novel methods combining
liquid chromatography with high resolution mass spectrometry have identified
approximately 200 unique oligosaccharides structures varying from 3 to 22 sugars. The
increasing complexity of oligosaccharides follows the general pattern of mammalian evolution
though the concentration and diversity of these structures in homo sapiens are
strikingly. There is also diversity among human mothers in oligosaccharides. Milks from
randomly selected mothers contain as few as 23 and as many as 130 different oligosaccharides.
The functional implications of this diversity are not known. Despite the role of
milk to serve as a sole nutrient source for mammalian infants, the oligosaccharides in milk
are not digestible by human infants. This apparent paradox raises questions about the
functions of these oligosaccharides and how their diverse molecular structures affect
their functions. The nutritional function most attributed to milk oligosaccharides is to
serve as prebiotics - a form of indigestible carbohydrate that is selectively fermented by
desirable gut microflora. This function was tested by purifying human milk oligosaccharides
and providing these as the sole carbon source to various intestinal bacteria. Indeed,
the selectively of providing the complex mixture of oligosaccharides pooled from human
milk samples is remarkable. Among a variety of Bifidobacteria tested only Bifidobacteria
longum biovar infantis was able to grow extensively on human milk oligosaccharides as
sole carbon source. The genomic sequence of this strain revealed approximately 700
genes that are unique to infantis, including a variety of co-regulated glycosidases, relative
to other Bifidobacteria, implying a co-evolution of human milk oligosaccharides and the
genetic capability of select intestinal bacteria to utilize them. The goal of ongoing
research is to assign specific functions to the combined oligosaccharide-bacteria-host
interactions that emerged from this evolutionary pressure.
Copyright / Drug Dosage
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