Prebiotics

Prebiotics are  defined as “selectively fermented  ingredients that allow specific changes, both in the composition and or activity in the gastrointestinal microflora that confer benefits upon host well-being and health [Roberfroid 2007]. Prebiotics are also defined as non-digestible to low-digestible food ingredients that benefit the host organism by selectively stimulating the growth or activity of one or more than but limited number of probiotic bacteria in the colon (Crittenden & Playne, 1996; Dimer & Gibson, 1998; Zimmer & Gibson, 1998; Manning & Gibson, 2004). This role is played by Fermentable carbohydrates, which are not digested or poorly digested in the small intestine and stimulate, preferentially, the growth of bifidobacteria and some Gram-positive bacteria, belonging to the probiotic bacteria administered to humans play this role. Complex carbohydrates traverse through the small intestine to the lower gut where they become available for some colonic bacteria but are utilized by only certain microbial types out of the majority of the bacteria present in the colon. Lactulose, galactooligosaccharides (GOS), Fructooligosaccharides (FOS), inulin and its hydrolysates, maltooligosaccharides, and resistant starch are the prebiotics commonly used in human nutrition. The main end products of carbohydrate metabolism by the way of fermentation by enzymes of Probiotic origin are short-chained fatty acids, namely acetate, butyrate and propionate, which are further used by the host organism as an energy source. In practice, the most common oligosaccharides are inulin and its hydrolysates and oligofructans.

The majority of studies have so far focused on inulin, FOS and GOS [Macfarlane et al., 2006;  Macfarlane et al. 2008]. These saccharides have now a long history of safe use and are generally regarded as safe, although there is some concern over increased gas production with some compounds, particularly when ingested in higher amounts or during the first few days of intake. They can be found in chicory, topinambuco, onion, garlic, asparagus, artichoke, leek, bananas, tomatos and many other plants.

Prebiotic oligosaccharides can be produced in three different ways: by extraction from plant materials, microbiological synthesis or enzymatic synthesis, as well as by enzymatic hydrolysis of polysaccharides (Crittenden & Playne, 1996; Gulewicz et al., 2003). In practice, combined mixtures of probiotics and prebiotics are often used because their synergic effects are conferred onto food products. For this reason, such mixtures are called synbiotics. In conclusion,  prebiotics are dietary substances (mostly consisting of nonstarch polysaccharides and oligosaccharides poorly digested by human enzymes) that nurture a selected group of microorganisms living in the gut. They favor the growth of beneficial bacteria over that of harmful ones.