A prebiotic is a selectively fermented ingredient that results in specific changes in the composition and/or activity of the gastrointestinal microbiota, thus conferring benefit(s) upon host health. (Gibson et al. 2010. Food Science and Technology Bulletin: Functional Foods 7 (1) 1–19.)
A huge and diverse range of bacterial species colonize the human body. The microbiota extend from mouth to anus and into the vaginal tract of women. They also reside on the skin. Many lines of research have demonstrated the significant role of the microbiota in human physiology. The microbiota are involved in the healthy development of the immune system, prevention of infection from pathogenic or opportunistic microbes and maintenance of intestinal barrier function. For a variety of reasons, normal native bacteria may not always perform these functions optimally. Probiotics or prebiotics have been studied and used to improve these functions.
To generalize, it is possible to categorize the gut microbiota components on the basis of whether they exert potentially pathogenic or health promoting aspects. Lactic acid producing genera such as the bifidobacteria or lactobacilli have a long standing association with health. These bacteria can be increased either by feeding appropriate strains as a probiotic or through the provision of prebiotic growth substrates.
The rapidly expanding research support and product availability for probiotics and prebiotics is evidence for their growing popularity. Probiotics and prebiotics are available commercially in many forms, including foods, dietary supplements, and clinical therapeutics with oral or non-oral delivery. To be effective, probiotics must be capable of being prepared in a viable manner and on large scale (e.g. for industrial purposes), whilst during use and under storage the probiotic should remain viable and stable. For most applications they should be able to survive in the intestinal ecosystem and the host animal should gain beneficially from harboring the probiotic. Clearly, the organisms used should be generally regarded as safe. Prebiotics must provide selective stimulation of the growth or activity of beneficial native bacteria. Since prebiotics are non-viable, stability is not a concern, but safe consumption levels must be established.