Medicinal value of liquid fermented milk products has been suggested for hundreds of years, and various studies have implied that individuals for whom fermented milks such as acidophilus milk, Bulgarian buttermilk, and kefir is a part of the diet as in some parts of Russia, live long lives (1). This value goes beyond the accepted high nutritional quality of unfermented milk. The fermentation process apparently adds therapeutic qualities to milk that are not found in the original milk. These properties are imparted by the cultures that have the ability to survive product manufacturing and storage procedures and the harsh environment in the gastric system and establish themselves in the intestinal tract. Through their activities in this environment they are able to perform functions that are of benefit to the consumer. Also, some metabolic products of their growth during the fermentation process add therapeutic value to the finished fermented product. For example, a pasteurized Japanese product (Ameal S) is produced by the fermentation of a milk-based medium with Saccharomyces cereviseae and Lactobacillus helveticus. The fermentation process produces two tripeptides, valine-proline-proline, and isoleucine-proline-proline, which have the ability to reduce blood pressure. In this product, live bacteria do not exist and are not important but the products of their growth are (48).
Much has been written about studies on the therapeutic value of fermented milks involving in vitro, animal, and human studies. Various benefits have been suggested, including the reduction in risk of gastrointestinal illnesses such as diarrhea, improved lactose digestion, enhancement of the immune function, decreasing Helicobacter pylori infection, reduction of cholesterol and certain allergies, anticarcinogenic action and so forth (49,50). As a result of this, commercial fermented milks with health claims have been developed in some countries and in Japan the Ministry for Welfare developed FOSHU (Foods for Specified Health Use) regulations in 1993 for such products (51).
Lactobacilli such as the types used in the manufacture of some liquid fermented milks described above have been linked to various therapeutic properties (12). Lactobacillus acidophilus, casei, and reuteri are believed to control the growth of undesirable microorganisms such as Escherichia coli and Salmonella spp. in the intestinal tract (50). A large amount of acid produced by these organisms is one method of such control, as is competitive exclusion, but these bacteria are also able to produce bacteriocins that are antagonistic against undesirable organisms. Lactobacillus acidophilus LB (52), Lactobacillus johnsonii LA1, and Lactobacillus casei YIT9209 (53) produce antimicrobial substances against Helicobacter pylori, which is a human gastric pathogen. The antibiotic reuterin produced by Lactobacillus reuteri is effective against a wide range of organisms including pathogens (50). Control of undesirable microorganisms that produce carcinogenic metabolites in the intestines may also result in anticarcinogenic effects by limiting the production of such metabolites (50).
Some lactic acid bacteria have been shown to stimulate immune functions by activating macrophages, increasing the levels of cytokines, and increasing immunoglobulin levels (especially those of IgA). Organisms identified in such functions include Lactobacillus johnsonii LA1, Lactobacillus GG, and Lactobacillus casei Shirota, among others (48).
The improvement of lactose digestion, for which Lactobacillus acidophilus has particularly been identified, is useful for individuals who are not able to digest lactose. Lactobacillus acidophilus, unlike yogurt bacteria, is able to survive and grow in the intestinal tract. Here the increased permeability of the bacterial cells allows for the permeation of lactose and subsequent hydrolysis by beta-galactosidase (50).
A reduction in serum cholesterol has also been linked to certain lactobacilli including acidophilus, johnsonii, and casei (50,54). This activity is believed to occur by the assimilation of cholesterol or via deconjugation of bile acids in the small intestine and subsequent excretion from the body. Bile acids are precursors for cholesterol; hence their removal from the body helps in reduction of cholesterol.
The therapeutic properties of traditional kefir have been identified as an increase in the excretion of urea and some nitrogen metabolism products (14) and the treatment of atherosclerosis, allergic disease, and gastrointestinal disorders (55). The polysaccharides are able to decrease the cholesterol content of blood and bind toxins. Anticancer effects of kefir have also been suggested (14). The inclusion of pre- and probiotics, as stated earlier, and colostrum products have expanded the therapeutic value of kefir.
Koumiss made from mare's milk has been used widely in Russia for many years for the treatment of tuberculosis (56,57), and chronic enteritis and gastrointestinal disorders (58). The first hospital specializing in koumiss therapy was established in 1858 in Samara, Russia. The intestinal microflora is apparently normalized with koumiss therapy and partly because of the intense yeast fermentation, the vitamin B12 absorption and levels in blood are raised (59). The dose for adults is 1.5 L per day and 0.4 to 0.8 L for children (1). Koumiss is readily digested and assimilated because of its lower casein content and a larger proportion of peptones and free fatty acids that are generated during fermentation.
Many of these therapeutic properties of fermented milks are strain specific—not all strains have all of the above characteristics. In the manufacture of fermented milk, therefore, it is important to use specific strains if health claims are made (60-62).
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