In recent times, the role of bioactive food components, including micronutrients, phytochemicals, zoochemicals, botanicals, prebiotics and probiotics have become an area of immense interest to health professionals and researchers. All these bioactive food components are referred to by the generic term ‘functional foods.’ Gibson and Roberfroid (1999) have defined functional food as “a dietary ingredient(s) that can have positive properties above its normal nutritional value.”
Among these functional components with accumulating scientific evidence of their health benefits are prebiotics and probiotics. A probiotic was defined, as early as 1974, by Parker, as “Organisms and substances, which contribute to intestinal microbial balance”. Later, Fuller (1989) redefined probiotics as: “A live microbial feed supplement which beneficially affects the host animal by improving its intestinal microbial balance.”
Currently, the term synbiotic is being used to denote: “A mixture of pro and prebiotics which beneficially affects the host by improving survival and implantation of live microbial dietary supplements in the gastrointestinal tract.”
Humans have not only approximately 1012 parenchymal cells, but also about 1012 bacteria on the skin, another 1010 in the mouth and 1014 in the gut. The gastro-intestinal tract (GIT) has more than 400 species, with a predominance of obligate anaerobes, largely Bacteriodes, Clostridium, Lactobacillus, E. coli and Bifidobacteria. Nutritional factors strongly influence the composition of the gut microflora.
Little is known about the way in which the probiotic organisms influence the gut flora and produce a beneficial effect on the host animal. Resistance to low pH, gastric juices, pancreatic juices and bile acids and ability to adhere to the intestinal epithelium may be useful features. These features may be strain-specific within a given species. Microbes in human probiotic preparations are largely lactic acid bacteria (LAB) such as Lactobacilli, Streptococci and Bifidobacteria. Among humans, in most situations, use of probiotics has resulted in increased fecal counts of bifidobacteria and lactobacilli, a decrease in fecal pH and a decline in those bacterial enzyme activities that are associated with the development of colon cancer.
Adhesion of bacteria to the gut epithelium does not ensure that an organism will permanently colonize the gut. Certain ingested probiotics do survive their passage through the GIT, but they are excreted from the colon to the feces, without over multiplication or death. Nevertheless, during their passage through the gut, they continue to be metabolically active, conferring their beneficial effects.
Experimental studies in humans show that bifidobacteria probiotics (strain unspecified) when given in fermented milk, survived to the extent of 23.5 10.4% of the administered dose. B. bifidum and L. bulgaricus have been found to be most resistant to stomach acid, with a half- life of approximately 140 minutes. The half-life of S. thermophilus and L. acidophilus was approximately 40 minutes.
The functional properties of probiotics include antimicrobial activity against pathogenic and non-pathogenic organisms and enhancement/balancing effect on immune response. Several studies indicate that some strains of LAB can enhance natural immunity when included in dietary formulations. It is evident from animal studies that immune enhancing effects include increased non-specific phagocytic activity against bacteria and enhanced myeloid and lymphoid cell cytokine production. Human studies indicate that LAB enhances peripheral blood phagocytic function and production of interleukins and interferons. Beneficial effects on natural immune function have been observed among the elderly on administration of Bif. lactis.
Besides, LAB has other characteristics, which are of advantage in clinical applications such as:
• Improved intestinal IgA responses
• Suppression of pathogen growth by secretion of bacteriocins
• No record of causing infection when administered as probiotics
• Low pathogenic potential
• Generally recognized as safe (GRAS) status
Due to these properties, probiotics show great promise for the management of many diseases including diarrhoeal disease, kidney disease, colon cancer, dental caries and infection with Helicobacter pylori, allergies and autism.
A number of research groups have studied the role of the microbiome and its effects on physiological systems and cellular metabolism using a variety of approaches focusing on (1) direct alterations of the microbiota, (2) treatment with prebiotics to select for growth of certain bacteria in the gastrointestinal (GI) tract and (3) treatment with probiotics to directly deliver beneficial bacteria to the GI tract.
Probiotics are being considered as one of the most efficient therapeutic tools for next generations. The reason behind this aspiration is their role in the maintenance of human health and treatment of various disorders ranging from bacterial infections, dermatitis, allergy, viral infections and many more. Role of probiotic microorganisms in development of innate immunity has been well characterized. Mechanism of action of probiotic function is not fully understood and under investigation in many cases. Few major mechanisms of action proposed through various studies are: production of antimicrobial compounds (Kelsall, 2008), Barrier function (Yan et al, 2006), competition for adherence (Johnson et al, 2007), immune modulation (Marn et al, 2003) and interference with quorum sensing signalling (Medellin et al, 2007).
The benefits of prebiotics on probiotic bacteria and ensuing physiological and systemic effects on health have increasing scientific evidence. However, the story is not as simple since both the structure and physicochemical properties of the non-digestible oligosaccharides or polyphenols impact the intestinal microbiota; further the beneficial effects of the probiotics seem strain specific. As nutritional factors strongly influence the composition of the gut microflora, the extent to which the food / biological matrix affect the prebiotics and probiotics, the processing and storage effects also need to be investigated.
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Dr. Usha Antony
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