Chemistry Reference
In-Depth Information
5.9.4.3.
Fermentation of Lactose Derivatives by the Intestinal Microbiota
In addition to modifying population dynamics, prebiotic lactose deri-
vatives also modify the activity of the microbiota by providing a source of
readily fermentable carbohydrate. It may be this dietary fibre-like character-
istic of modifying the fermentative activity of the existing microbiota that is
the important factor in providing a number of health benefits to consumers.
The proposed health effects of prebiotics believed to be largely contingent on
modifications to the metabolic activity of the microbiota include reductions
in risk factors for colon cancer, increased mineral absorption, improved lipid
metabolism and increased resistance to intestinal pathogens.
5.9.4.4.
Colon Cancer
The intestinal microbiota has a number of biochemical activities relevant
to colon cancer risk that relate to the composition and activity of different
bacterial populations. Hence, lactose-derivative prebiotics may have a role in
reducing risk factors for colon cancer. Proposed mechanisms include supplying
the colonic epithelium with SCFA (particularly butyrate); suppression of
microbial protein metabolism, bile acid conversion and other mutagenic and
toxigenic bacterial reactions; and immunomodulation (Figure 5.8).
A number of studies on humans and animals have shown that the
consumption of lactulose (Terada et al., 1992; Ballongue et al., 1997; De Preter
et al., 2004) and GOSs (Rowland and Tanaka, 1993; Kawakami et al., 2005)
improves the colonic environment in terms of reducing the levels of mutagenic
enzyme activities (e.g.,
-glucuronidase and azoreductase) and bacterial meta-
bolites (e.g., secondary bile acids, phenols and indoles) that are purportedly
associated with risk of colon cancer. However, the quantitative importance of
these markers to eventual cancer development remains to be established.
Protection by prebiotics against the development of pre-neoplastic
lesions and tumours in rodent models of colon carcinogenesis has also been
reported for lactulose (Rowland et al., 1996; Challa et al., 1997), while in a
human feeding study, administration of lactulose reduced the recurrence of
colonic adenomas in patients who had had surgery to remove adenomas
(Ponz de Leon and Roncucci, 1997). However, these results are very pre-
liminary and a great deal more research is required to discern if the consump-
tion of lactulose has a protective function against colorectal cancer.
5.9.4.5.
Mineral Absorption
Encouraging results have been reported for the impact of fermentable
carbohydrates, including GOSs and lactulose, on increasing mineral absorption
from the gut. The precise mechanisms of prebiotic-mediated improvements in
