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Prebiotic effect of yacon (Smallanthus Sonchifolius) on intestinal microbiota,
mucosal immune system and in the prevention of intestinal infections
María Eugenia Bibas Bonet1, Eva María Velez1, Oscar Meson1 and Gabriela Perdigón1.2
1- Instituto de Microbiología. Facultad de Bioqca , Qca y Farmacia. UNT
2- CERELA-CONICET
In the last decades, there has been an increasing interest in the relation between colonic
function and health. There are literatures suggesting that large amounts of unrefined
plant foods, especially all starchy foods rich in dietary fibre, may offer protection
against several diseases of the large intestine.
Dietary carbohydrates that escape digestion in the small intestine undergo bacterial
fermentation in the colon. This process affects the microbial ecology of the
gastrointestinal tract and influences gut metabolism and function.
Prebiotics are non-digestible but fermentable oligosaccharides that are specifically
designed to change the composition and activity of the intestinal microbiota with the
prospect to promote the health of the host. Their fermentation results in the acidification
of the colonic contents and the formation of short chain fatty acids which serve as fuels
in different tissues and may play a role in the regulation of cellular processes. Prebiotics
specifically stimulate the growth of endogenous microbial population groups such as
bifidobacteria and lactobacilli which are perceived as being beneficial to human
health.The concept of prebiotics arose from the observation that inulin and
fructooligosaccharides selectively stimulate the growth of bifidobacteria. Other nondigestible oligosaccharides (NDO) including xylooligosaccharides,
galactooligosaccharides and isomaltooligosaccharides have also been tested for their
prebiotic effect. The majority of candidate prebiotics are oligosaccharides but also
include polysaccharides. To serve as a bacterial substrate in the colon, a prebiotic may
not be hydrolyzed or absorbed in the upper part of the gastrointestinal. Some studies
reported also potential immune-modulating properties to the prebiotics.
Smallanthus sonchifolius (yacon), originating from South America, has become popular
in Japan and in New Zealand for its tubers which contain beta-1,2-oligofructans as the
main saccharides. The plant is also successfully cultivated in Central Europe,
particularly in the Czech Republic.
However, additional studies are needed to show that prebiotics and specially yacon can
directly or indirectly stimulate intestinal host defenses.
We evaluated the prebiotic property of yacon root flour and its influence on the
intestinal microbiota and the gut immune system using a mice model, after a long-term
daily consumption. We analyzed the intestinal microbiota mainly focus in bifidobacteria
population. The effect on total IgA in intestinal fluid, the number of IgA +, Th1+ and
Th2+ cell populations, the cells producing IL12, IL10, IL4 and IFN measured in the
lamina propria of the small and large intestine, as well as the number of mast cell were
evaluated. Histological studies of the gut, to evaluate possible modifications in this
tissue due to the long term of yacon administration, and the protection against
Salmonella infection were also analyzed.
The results show the prebiotic effects of yacon root flour, stimulating the growth of
bifidobacteria and lactobacilli in the large intestine of the mice. In the intestinal immune
system, we observed an increase in total IgA, in the number of IgA+ cells, mast cells,
IL4, IL10 and IFN producing cells, and no effect in the number of Th1 and Th2
populations.
Long term of yacon root flour administration maintained the intestinal homeostasis
without inflammatory effects, regulated mainly through IL-10 and IL-4 regulatory
cytokines.
As regard the protective effect against Salmonella enterica serovar Typhimurim
infection, we observed that there was not a correlation between the number of IgA+
cells and the secretion of specific antibodies against the pathogen. The TLR4+,
CD206+, IL6+ and MIP 1+, TNF
were increased in the lamina

propria of the small intestine, as well as the phagocitic activity of the peritoneal
macrophages. We demonstrated that fructooligosaccharides from Yacón roots prevent S.
Typhimurium infection up to 30 days of administration through non-specific immunity
with increased total s-IgA, expression of TLR4 and CD206 receptors, IL6+ and MIP1α
+ cells, that would improve immunological barrier mechanisms against S. Typhimurium
infection.