Probiotics are defined as oral probiotics are living micro-organisms which, upon digestion in certain numbers, exert health benefits beyond inherent basic nutrition. In addition to this, according to FAO/WHO, probiotics are;
‘Live microorganisms which when administered in adequate amounts confer a health benefit on the host’
The three main aspects of the definition are:

• the micro-organisms (bacteria) are alive
• the bacteria are administered orally
• the bacteria should be capable of reaching the intestine alive, in order to have an influence on the microbial balance

This means that probiotic bacteria should be resistant against acid (stomach), bile, capable of growing under anaerobic conditions and be non-toxic. These criteria limit the number of bacterial species and strains to the following groups of bacteria: Lactobacillus, Streptococcus and Bifidobacterium species, although some other species can be used in some cases (such as yeasts and Bacillus species in animal nutrition). All three genera are part of the lactic acid bacteria and are naturally present in the intestine as well as in many fermented (mainly acid) dairy products.

Prebiotics are defined as:

Non digestible food ingredients, that beneficially affect the host by selectively stimulating the growth and/or activity of one or a limited number of bacteria in the colon, and thus improve host health.

Most potential prebiotics are carbohydrates, but the definition does not exclude non-carbohydrates to be used as a prebiotic. In theory, any antibiotic that would reduce the number of potentially harmful bacteria and favour health promoting bacteria or activities, can be considered a prebiotic.

The definition does not emphasize a specific bacterial group. Often, however, it is assumed that a prebiotic should increase the number and/or activity of bifidobacteria and lactic acid bacteria, as these groups of bacteria are claimed to have several beneficial effects on the host. A product that stimulates (or claims to stimulate) bifidobacteria is considered a bifidogenic factor. Some prebiotics may thus also act as a bifidogenic factor and vice versa, but the two concepts are not identical.

Prebiotics are specifically targeted to act on the flora in the large intestine.
The following effects of prebiotics have been claimed:

• relief of constipation
• reduce intestinal pH
• restore intestinal bacterial balance
• effect blood cholesterol level
• reduce risk on colorectal cancer
• effects on the immune system

Commercial prebiotics
Most commercial prebiotics are oligosaccharides and dietary fibres. Selected non-digestible oligosaccharides will increase the carbohydrate fermentation and thus be effective for most of the claims described above. However, it should be kept in mind that not all oligosaccharides will have a beneficial effect. To have an effect a (mixture of) oligosaccharide(s) should be thoroughly tested in animals and humans.

At present, there are no oligosaccharides that selectively stimulate a certain group of bacteria. It has been claimed that several oligosaccharides selectively stimulate bifidobacteria and lactic acid bacteria, but experiments in vivo (in humans) and in vitro (laboratory) have shown that all commercial oligosaccharides are fermented by a large number of bacterial species in the intestine.

All commercial oligosaccharides, when effective, thus act by changing the metabolism, not by selectively stimulating a certain bacterial group.

References
http://en.wikipedia.org/wiki/Probiotics
http://www.food-info.net/uk/ff/prebiotics.htm
http://www.food-info.net/uk/ff/probiotics.htm
http://en.wikipedia.org/wiki/Prebiotic_(nutrition)

Back