Probiotic bacteria are important functional foods capable of improving consumer health. Although most probiotic bacteria are derived from human intestinal flora, they are not indigenous to all individuals. It is very likely that probiotic bacteria are seen as exogenous or foreign antigens by the gut immune system. In research on orally administered lactic acid bacteria, it was found that serum antibody responses were induced not only against the whole bacterial cell, but also against cytoplasmic components. Mucosal immune responses were induced against cytoplasmic antigens and may be of relevance in the development of mucosal vaccines using lactic acid bacteria. These bacteria also exert an adjuvant effect on the mucosal IgA response against not only pathogenic organisms, but also dietary antigens. Furthermore, they enhance systemic immune responses such as phagocytic activity and serum antibody production. These biological responses have been shown in human studies and have formed the basis for oral bacteriotherapy with probiotic bacteria. Since the immunopotentiating activity of lactic acid bacteria is strain-dependent, it is important that special efforts be directed to selection criteria used for the identification of biologically active strains with probiotic function.
Up to 80% of the body's immune system is localized in the gastrointestinal tract. This offer unique opportunities to modulate the immune response and prevent disease by eating right. Among the substances regarded as having positive effects are many thousand antioxidants, not only traditional vitamins but numerous flavonoids, carotenoids and similar plant-and vegetable produced antioxidants. Also health-promoting bacteria (probiotics) and numerous plant and vegetable fibres (prebiotics) are increasingly documented to have strong health-promoting influence. The intestine harbours about 300, 000 genes, to be compared to the about 60, 000 in the rest of the body. This is an indication of the enormous chemical activity going on in the intestine. One can anticipate that there are several times more enzymes active in the intestine than in the rest of the body. These enzymes release 100, 000 or more of substances, which are absorbed and hereby serving as health-promotors in the body. Among these are antioxidants, but also amino acids, polyamines, short chain and other long chain fatty acids, various carbohydrates etc. In addition do the microbial cells produce signal molecules, called bacteriokines, with which the microbes communicate both with the mucosal cells and the immune system. The world of fermentation products, often referred to as synbiotics are poorly investigated and understood. It is a priority task for this new millennium to explore and understand the production of synbiotics and their role both for human and animal health, well-being, performance and long life.
While a myriad of healthful effects have been attributed to the probiotic lactic acid bacteria, perhaps the most controversial remains that of anticancer activity. There is no direct experimental evidence for cancer suppression in humans as a result of consumption of lactic cultures in fermented or unfermented dairy products. However, there is a wealth of indirect evidence, based largely on laboratory studies, in the literature and this will be summarised in the present paper. Reports in the literature, regarding the anticancer effects of lactic acid bacteria, fall into the following categories: in vitro studies, in vivo studies in laboratory animals, epidemiological studies correlating cancer and certain dietary regimes and dietary intervention studies in human volunteers.
Yogurt supplemented with brewer's yeast cell wall (BYC) was administered to 24 constipated female volunteers, and the effect on the stool frequencies, fecal quantities, fecal characteristics, and fecal microflora were examined. Yogurt contained 6 g of BYC per 200 ml, and the other batch without BYC served as control diet. The volunteers ingested BYC-yogurt (BYC-Y) or control yogurt (CONT) every day for one week in a crossover experiment. Stool frequencies and fecal quantities of the subjects during the entire period of BYC-Y intake were found to be significantly higher than those under the CONT diet. It was observed that the proportion of Bifidobacterium in the fecal microflora significantly increased (p<0.05), and those of Clostridium perfringens and Streptococcus significantly decreased (p<0.05) with the ingestion of BYC-Y. The fecal water content and levels of short-chain fatty acids (SCFAs) in feces were also higher in subjects with BYC-Y intake than in CONT diet. Furthermore, because of the fermentation of SCFAs, BYC-Y administration significantly lowered fecal pH. A similar effect was observed with CONT intake; however, it was less evident than in the BYC-Y intake. These results indicate that the BYC-Y intake is effective to prevent the constipation. Furthermore, these findings suggest that the synergistic effects of beneficial bacteria in yogurt and BYC in improving the intestinal environment and bowel movement. These effects of BYC are related to such properties as fermentation, water-holding capacity, and swelling force in the large intestine.