Chemistry Reference
In-Depth Information
Mouth
Mouth:
no breakdown by saliva / dental flora
Stomach:
no acid hydrolysis
Small intestine:
no enzymatic hydrolysis
no absorption
Colon:
fermentation by bifidobacteria /
lactobacilli
Figure 4.3
the digestibility of gos. (from nauta and schoterman, 2009. With permission.
10
)
of the small and large bowel. Some members of the microbiota play a role in the
modulation of mucosal and systemic immune functions with an impact extending
that of the intestine.
A healthy microbiota is considered one that is predominantly carbohydrate
fermenting (saccharolytic) and that is comprised of significant numbers of bifido-
bacteria and lactobacilli. Both species have been linked to increased resistance to
infections and diarrheal disease, stimulation of immune system activity, protection
against colon cancer, and the synthesis of various vitamins. The products of the sac-
charolytic fermentation, principally SCFAs, have a positive impact on colon physiol-
og y.
21
The metabolism of peptides and proteins (putrefaction) by other anaerobes
also produces SCFAs, but, in addition, generates potentially toxic substances (e.g.,
biogenic amines and sulfides, ammonia, phenols, thiols, and indols) that can increase
the risk of colon cancer.
An important factor influencing the composition of the microbiota is nutrition, as
exemplified by the differences between breastfed and standard formula-fed infants.
Whereas breastfed infants have a microbiota dominated by bifidobacteria (up to 95
percent), standard formula-fed infants have a more complex (and less stable) flora,
which more resembles the adult gut.
19
The latter also have higher fecal levels of poten-
tially harmful bacterial metabolic by-products.
22
These differences are, most likely,
due to the supply of human milk oligosaccharides (HMOs) present in breast milk.
19
GOS have been shown to positively influence both the composition and activity
of the microbiota. Through their effect on the microbiota, GOS also affect the activ-
ity of the immune system. In addition, GOS have various other effects that positively
