Chemistry Reference
In-Depth Information
6.2 rs As PrEbIoTICs
A prebiotic is “a selectively fermented ingredient that allows specific changes,
both in the composition and/or activity in the gastrointestinal microflora that confers
benefits upon host well-being and health,” whereas synergistic combinations of pro-
and prebiotics are called synbiotics (Gibson and Roberfroid, 2008). Nondigestible
oligosaccharides (particularly inulin, its hydrolysis product oligofructose, (
trans
)
galacto-oligosaccharides, and resistant starch) meet the criteria for prebiotic clas-
sification. These fibers have shown a positive impact on the intestinal microflora.
Other indirect health effects of prebiotics, mediated by the intestinal microflora, may
include prevention of diarrhea or obstipation, modulation of the metabolism of the
intestinal flora, cancer prevention, positive effects on lipid metabolism, stimulation
of mineral adsorption, and immunomodulatory properties.
In the large intestine, RS is fermented by intestinal bacteria to produce SCFAs,
particularly butyrate (Binder and Ramakrishna, 1998; Cummings et al., 1996;
Topping et al., 2003). Some data suggest that the colonic microflora may adapt to
produce more butyrate if given time and the proper substrate (Silvi et al., 1999). The
fermentation of these RS led to
in vitro
SCFAs levels (acetate, propionate, butyrate)
of 2,000 to 2,500 μmol/g feces dry weight with butyrate contents of 30 to 60 mol%
(Schmiedl et al., 2000).
In human studies, RS2 and RS3 from HACS results in selective colonic microflora
activity as well as increased fecal butyrate concentrations (Brown et al., 1997, 1998;
Wang et al., 2002; Jacobasch et al. 2006; Finocchiaro et al., 2009). Thus, RS can be
considered a prebiotic because it promotes health of the host through fermentation.
Jacobasch et al. (2006) demonstrated that RS3 (Novelose
®
330 starch) was well
fermented in the cecum and proximal colon in rats, whereas the degradation of
hydrothermally treated RS3 (hydrothermally treated Novelose) took place beyond
the cecum and increased continuously through the colon to favor SCFA production
in the distal colon. Corresponding to the high rate of hydrothermally treated RS3 fer-
mentation in the distal colon, the SCFA concentrations in the feces and the growth of
bacteria increased significantly, resulting in a nearly twofold increase in wet content.
An exchange of 10 percent starch with a butyrogenic RS3 in the diet was proved to
be sufficient to provide enough substrate for bacterial fermentation in the distal colon
and rectum. As SCFA concentration increased, the pH decreased in the large bowel.
Consumption of RS3 lowered the pH in the cecum and proximal colon to 6.5 to 6.6
from 7.5 (control diet) and intake of hydrothermally treated RS3 lowered the pH in
the distal part of the colon to 6.3.
Wang et al. (2002) demonstrated that different amylomaize starches could gener-
ate desirable variation in gut microflora in mice. In this study the effects of HACS
and modified (carboxymethylated and acetylated) HACS on the composition of
colonic bacteria and the production of volatile fatty acids was investigated in mice.
All starches tested showed the increases in indigenous bifidobacteria in mice fed
although 40 percent unmodified HACS showed the highest numbers. High-amylose
cornstarch increased
Lactobacillus
numbers in the mice colon and acetylated HACS
