What are Prebiotics?
Gibson & Roberfroid first used the term Prebiotic in 1995 (J. Nut.) to designate “Non-digestible nutritional ingredients that beneficially affect the host, selectively stimulating the growth and activity of one or more beneficial bacteria in the colon, improving the host’s health”.
The main action of Prebiotics is to stimulate the growth and/or activate the metabolism of some group of beneficial bacteria in the intestinal tract. In this way the Prebiotics act in an intimate relationship with the Probiotics, constituting the “food” of the probiotic bacteria.
The use of products denominated Prebiotics in association with Probiotics presents greater beneficial action than the growth promoting antibiotics, notably not leaving residues in products of animal origin and not inducing the development of drug resistance, since they are essentially natural products.
General characteristics of Prebiotics:
- They should not be metabolised or absorbed during their passage through the short intestine;
- They should serve as the substrate for one or more beneficial intestinal bacteria (these will be stimulated to grow and/or become metabolically active);
- They should possess the capacity to alter the intestinal microflora so as to favour the health of the host;
- They should induce beneficial effects systemically or in the host’s intestinal lumen.
Prebiotic substances
Some sugars, absorbable or otherwise, fibres, sugar alcohols and oligosaccharides are within this concept of prebiotics. Of these, the oligosaccharides – short-chain polysaccharides consisting of 3 to 10 inter-connected simple sugars - have received more attention due to the innumerable prebiotic properties attributed to them.
The fructooligosaccharides are polysaccharides that have demonstrated excellent prebiotic effects, selectively “feeding” some species of Lactobacillus and Bifidobacterium and thus reducing the amounts of other bacteria such as Bacteroides, Clostridium and Coliforms.
Arabinose, galactose, mannose and principally lactose, are other carbohydrates used as Prebiotics in poultry. Lactose, added to the feed together with a Probiotic, reduces colonisation by salmonellas.
Sources of Oligosaccharides
The prebiotics can be found in the natural form in the seeds and roots of some vegetables such as chicory, onion, garlic, artichoke, asparagus, barley, rye, soybeans, chick peas and lupine beans, and can be extracted by cooking or by the action of enzymes or alcohol. Synthetic oligosaccharides are also available, obtained by the direct polymerisation of some disaccharides from the yeast cell wall or by the fermentation of polysaccharides. The synthetic oligosaccharides have presented better results as prebiotics, showing less side effects.
How the Prebiotics act
As already mentioned, prebiotic substances act by feeding and stimulating the growth of various beneficial intestinal bacteria, whose metabolisms act, reducing the pH by increasing the amount of organic acids present in the caecum. On the other hand, they act by blocking binding sites (principally D-mannose), immobilising and reducing the binding capacity of some pathogenic bacteria onto the intestinal mucous. It has been speculated that the oligosaccharides can also act by stimulating the immune system via the indirect reduction of intestinal translocation by pathogens, which would result in infections after reaching the blood stream.