Kefir – a complex probiotic
Edward R. Farnworth
Food Research and Development Centre, Agriculture and Agri-food Canada, St. Hyacinthe, Quebec, Canada J2S 8E3.
Kefir is a fermented milk drink produced by the actions of bacteria and yeasts contained in kefir grains, and is reported to have a unique taste and unique properties. During fermentation, peptides and exopolysaccharides are formed that have been shown to have bioactive properties. Moreover, in vitro and animal trials have shown kefir and its constituents to have anticarcinogenic, antimutagenic, antiviral and antifungal properties.
Although kefir has been produced and consumed in Eastern Europe for a long period of time, few clinical trials are found in the scientific literature to support the health claims attributed to kefir. The large number of microorganisms in kefir, the variety of possible bioactive compounds that could be formed during fermentation, and the long list of reputed benefits of eating kefir make this fermented dairy product a complex probiotic.
Many probiotic products have been formulated that contain small numbers of different bacteria. The microbiological and chemical composition of kefir indicates that it is a much more complex probiotic, as the large number of different bacteria and yeast found in it distinguishes it from other probiotic products. Since the yeasts and bacteria present in kefir grains have undergone a long association, theresultant microbial population exhibits many similar characteristics, making isolation and identification of individual species difficult. Many of these microorganisms are only now being identified by using advanced molecular biological techniques. The study of kefir is made more difficult, because it appears that many different sources of kefir grains exist that are being used to produce kefir.
The production of kefir depends on the synergistic interaction of the microflora in kefir grains. During the fermentation process, the yeasts and bacteria in kefir grains produce a variety of ingredients that give kefir its unique taste and texture. After fermentation, the finished kefir product contains many ingredients that are proving to be bioactive. At least one exopolysaccharide has been identified in kefir, although others may be present. Many bacteria found in kefir have been shown to have proteinase activity, and a large number of bioactive peptides has been found in kefir. Furthermore, there is evidence to show that kefir consumption not only affects digestion, but also influences metabolism and immune function in humans.