Chemistry Reference
In-Depth Information
11.2 PrEbIoTICs AND FErMENTATIoN
Gibson and Roberfroid have refined their original definition of a prebiotic whereby
“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.”
3
The original definition of a prebiotic
took into account only the associated microbial changes in the colon;
4
however, the
current proposed definition considers the additional health benefits associated with
the targeted stimulation of particular microorganisms. Any substrates or food com-
ponents that are not digested may enter the colon intact and be a potential prebiotic.
However, to be classified as a prebiotic, three criteria must be met. These include (1)
resistance to gastric acidity, digestion, and absorption; (2) fermentation by intestinal
microflora; and (3) selective stimulation of the growth and/or the activity of those
intestinal microflora that contribute to the health and well-being of the host.
5
To date, much of the interest in prebiotics has been focused on nondigestible
oligosaccharides, specifically inulin-type fructans, such as inulin and oligofructose,
which meet all three criteria for classification as prebiotics. Inulin-type fructans
are oligo- or polymers of d-fructose joined by β(2-1) bonds with an α(1-2) linked
d-glucose at the terminal end. Oligofructose is referred to those with degrees of
poly-merization (DP) between 3 to 10, and inulin to those with a DP between 10 and
65.
6
Other possible candidates, such as gluco-oligosaccharides, isomalto-oligosac-
charides, lactosucrose, polydextrose, soybean oligosaccharides, and xylo-oligosac-
charides, are being investigated for their prebiotic activity.
5
The nondigestible and fermentable nature of inulin-type fructans has been shown
to selectively stimulate the growth of specific bacteria that are beneficial to health,
especially bifidobacteria and lactobacilli, which have defined metabolic functions.
7
In
studies involving patients with ileostomies, inulin and oligofructose have been shown
to be resistant to hydrolysis and 88 and 89 percent, respectively, are recovered in the
effluent in the intact unhydrolyzed form.
8,9
Furthermore, inulin and oligofructose are
not recovered in the feces suggesting they are completely fermented in the colon.
10,11
This is supported by studies using various
in vitro
fermentation systems, with mixed
or pure cultures of human fecal microflora, demonstrating that the fermentation of
both inulin and oligofructose result in the selective stimulation of bacterial growth,
specifically bifidobacteria.12-14
12-14
In a study by Gibson et al.,
15
intake of 15 g/day of
oligofructose or inulin for 15 days resulted in a significant increase in bifidobacte-
ria from 8.8 to 9.5 log
10
/g stool and 9.2 to 10.1 log
10
/g stool, respectively. The total
bacterial counts remained unchanged indicating that the increase in bifidobacteria
resulted in a shift in the balance of microflora in the large intestine, where decreases
in bacteroides, clostridia, and fusobacteria were observed.
15
Numerous human stud-
ies with varying dose, substrate, duration, and subject population have also resulted
in similar outcomes of increased fermentation and bifidobacteria.15-22
15-22
Furthermore,
increases in breath hydrogen excretion, as an indirect marker of colonic fermenta-
tion, have also been observed with intake of oligofructose and inulin.
11,15,23
It has
