PREBIOTICS

Prebiotics are food ingredients, particularly, certain dietary fibres or oligosaccharides that cannot be digested other than by some specific bacteria and are involved in selectively stimulating the growth and / or activity of good bacteria (i.e. probiotics) to benefit he health of the host.

Although different authors give different definitions for prebiotics, the classical definition of prebiotics was given by Gibson and Roberfroid, who in the year 1995, defined prebiotics as non digestible food components, usually oligosaccharides, which evade digestion by mammalian enzymes, in the upper regions of the gastro intestinal tract, reach the colon in an intact state and are metabolized by the beneficial members of the indigenous microbiota.

Later, Gibson and MacFarlance, in the year 1994, clarified that selective fermentation of prebiotics by such microorganisms must result in a healthier composition of the gut microflora and induce luminal or systemic effects, beneficial to the host.

PREBIOTICS and THEIR TYPES

Prebiotics could also be termed as colonic foods, i.e. foods that pass the large intestine (i.e. colon) and which serves as substrates for the endogenous bacteria colonizing colon, thereby indirectly providing the host with the much need energy, metabolic substrates and essential nutrients. Generally resistant starch and non starch polysaccharides are classified as “colonic foods” but not as prebiotics, as they are not metabolized and utilized by the available prebiotic bacteria which are limited in number.

However, some non digestible oligosaccharides are classified as both colonic foods and prebiotics. Fructo-oligosaccharides, transgalactosylated disaccharides and soybean oligosaccharides are the only products recognized widely and are used as food ingredients that meet all the requisites of prebiotic classification.

Classification of some naturally occurring and synthetic prebiotics and their sources are given below in the table as described by Rosenberg.

Sl.No	Classification	Origin / Manufacturing Procedure
I	Disaccharides
1	Lactulose	Lactose synthetic
2	Lactitol	Lactose synthetic
II	Oligosaccharides
1	Fructo- oligosaccharides	Legumes, vegetables, extracts/ hydrolysis of cereals.
2	Soybean oligosaccharides	Extraction / hydrolysis of soy bean
3	Xylo-oligosaccharides	Plant sources
4	Trans Galacto-oligosaccharides	Lactose synthetic
III	Polysaccharides
1	Inulin	Extracts obtained from legumes, vegetables and cereals.
2	Resistant starches	Extracts obtained from legumes, vegetables and cereals.