Chemistry Reference
In-Depth Information
gangliosides and sialoglycoproteins is significantly higher in breast-fed than in
formula -fed infants; this may be due to a difference between human milk and
infant formula with respect to their content of sialic acid (Wang et al., 2003).
When piglets were supplemented with increasing amounts of sialic acid as
casein glycomacropeptides for 35 days, there were proportionate increases in
protein-bound sialic acid concentrations in the frontal cortex and improve-
ments in learning (Wang et al., 2007). These observations support the notion
that the sialic acid of milk oligosaccharides and also of sialoglycopeptides can
be absorbed and utilized despite the fact that most milk oligosaccharides are
considered to be indigestible within the small intestine.
It would be of interest to investigate whether, and to what extent, other
monosaccharides, such as fucose, that are constituents of the neutral milk
oligosaccharides, can similarly be absorbed and used as biosynthetic precur-
sors. Rudloff et al. (2006) recently fed
13
C galactose to breast-feeding women
and determined the amount of
13
C incorporated into lactose and both neutral
and acidic oligosaccharides, notably LNT and fucosyl LNT. Incorporation of
13
C was also observed in the fraction containing difucosyl LNT, fucosyl LNH
and difucosyl LNH (Rudloff et al., 2006). These results should make it
possible to feed
13
C-enriched milk oligosaccharides to infants, thus facilitat-
ing studies on their metabolic fate.
8.6.
Bifidobacterium Growth Stimulation by Human Milk
Oligosaccharides
As noted above, although a small fraction of human milk oligosaccharides is
known to be absorbed intact, it is now generally accepted that the major part
survives passage through the small intestine and enters the colon. At this
location, they are believed to act as prebiotics, stimulating the growth of
bifidobacteria, and as soluble receptor analogues that inhibit the attachment
of pathogenic microorganisms to the colonic epithelial cells. Bifidobacterium
longum ssp. infantis has recently been shown to ferment purified human milk
oligosaccharides in vitro as a sole carbon source, whereas another gut com-
mensal, Lactobacillus gasseri, did not; this supports the hypothesis that human
milk oligosaccharides selectively amplify specific bacterial populations in the
infant intestine (Ward et al., 2006; Ninonuevo et al., 2007). There is evidence
that the metabolic activity of the bifidobacteria reduces the colonic pH, which
has the additional effect of inhibiting the proliferation of pathogenic organisms
such as Shigella flexneri and Escherichia coli (Gopal and Gill, 2000). It has
recently been shown that this strain is able to grow on human milk oligosac-
charides as the only carbon source (Ward et al., 2007). The degradation of these
oligosaccharides was studied during the growth of B. longum ssp. infantis
