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Basic concepts / Prebiotics
Prebiotics
"Among the natural nondigestible oligosaccharides that fulfill the criteria of a colonic food, fructooligosaccharides are the only products presently recognized and used as food ingredients that meet all the criteria allowing classification as prebiotics(1)." ]
FOS can be used as a natural sweetener, and many food and beverage companies are adding FOS to yogurt, cereal, cookies, fortified juice and water, as well as to bread.
Prebiotics have important functions in the body. Their main function is to stimulate the growth of beneficial bacteria in the large intestine(1). In particular, research has confirmed that prebiotic FOS selectively stimulates the proliferation of bifidobacteria(2,3).
On the other hand, the presence of undigestible carbohydrates induces a change in the global bacterial metabolic activity in the colon that results on rising carbohydrate fermentation.
Prebiotics increase beneficial native bacteria number and/or increase carbohydrate fermentation.]
The principal substrates for colonic bacterial growth are dietary carbohydrates which have skipped digestion in the upper gastrointestinal tract. These may originate from either from the diet or to the endogenous secretions, and include both carbohydrates and proteins(1)
Whilst the products of gut proteolysis ( protein fermentation) may be generally thought as toxic or potentially harmful for the host health, those products of saccharolytic digestion (carbohydrate fermentation) should be considered benign (Figure 1)(2).
It is thus beneficial to increase the carbohydrate fermentation and to suppress the protein fermentation(2). However, this fact does not necessarily correlate with an increase in number of the possible beneficial bacterial groups.
" A prebiotic is a non digestible food ingredient that beneficially affects the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improves host health"(1).
| This concept was introduced by Gibson in 1995. He also described that " In order for a food ingredient to be classified as a prebiotic, it must: | |
| 1. | be neither hydrolyzed nor absorbed in the upper part of the gastrointestinal tract; |
| 2. | be a selective substrate for one or a limited number of beneficial bacteria commensal to the colon, which are stimulated to grow and/or are metabolically activated; |
| 3. | consequently, be able to alter the colonic flora in favour of a healthier composition; |
| 4. | induce luminal or systemic effects that are beneficial to the host health".(1) |
A prebiotic substrate is selectively fermented by beneficial species of the indigenous gut flora, but will not promote increases in the number of potential pathogens(1). Thus, oral consumption of prebiotics can be an alternative or complementary method to probiotic supplementation in the efforts done to increase the number of bifidobacteria and lactobacillus in the colon, creating a healthier microflora composition(2).
Most prebiotics are non-digestible oligosaccharides (NDOs). NDOs are s hort-chain carbohydrates that are not digested in the small intestine and they reach the large intestine unaltered. Fructo-oligosaccharide (FOS), inulin, oligofructose, trans-galacto-oligosaccharide, isomalto-oligosaccharide, xylo-oligosaccharides, lactulose, manno-oligosaccharides (beneficial effects described in animals) and gluco-oligosaccharide are some examples of potential prebiotics. FOS are chain polymers of the sugar fructose that are naturally occurring in a variety of foods such as onion, garlic, oats, chicory root, barley, Jerusalem artichoke, leeks, and rye(1).
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