Fermented milk, lactic acid bacteria

Park, H. S. and Marth, E. H. 1972A. Behavior of Salmonella typhimurium in skimmilk during fermentation by lactic acid bacteria. J. Milk Food Technol. 35, 482-488. 

Kim, Y. J., and Liu, R. H. 2002. Increase of conjugated linoleic acid content in milk by fermentation with lactic acid bacteria. J. Food Sci., 67,1731-1737. 

Vutanen, T., Pihlanto, A., Akkanen, S., Korhonen, H. (2007). Development of antioxidant activity in milk whey during fermentation with lactic acid bacteria. Journal of Applied Microbiology, 102,106-115. 

Cells of microorganisms have constituted a portion of human food siace ancient times. Yeast-leavened baked products contain the residual nutrients from the yeast cells destroyed duriag bakiag (see Bakery processes and leavening agents). Cultured dairy products, such as yogurt, buttermilk, and sour cream, contain up to lO cells of lactic acid bacteria per gram (19) (see Milk and milkproducts). Other examples of fermented foods consumed siace early times iaclude fermented meats, fish, and soybean products. 

Lactose is mainly used as a fermentation substrate for lactic acid bacteria in dairy products, such as yogurt and cheese. These bacteria break down lactose into lactic acid, which solidifies the milk, and creates an acid environment that favors the benign lactic acid bacteria over those that are more harmful. 

Fermentation of lactose during the growth of micro-organisms in milk has a major effect on its redox potential. The decrease in the h of milk caused by the growth of lactic acid bacteria is shown in Figure 11.3. A rapid decrease in h occurs after the available 02 has been consumed by the bacteria. Therefore, the redox potential of cheese and fermented milk products is negative. Reduction of redox indicators (e.g. resazurin or... 

Fermented milks are cultured dairy products manufactured from whole, partly skimmed, skim, or slightly concentrated milk. Specific lactic acid bacteria or food-grade acids are required to develop the characteristic flavor and texture of these beverages. Fermented milks are either fluid or semifluid in consistency, with various proportions of lactic acid. Fermented products are regulated by federal standards in the United States, as stated in Table 2.2. Other fermented milks without established federal standards are regulated by state standards. Compositional standards for fermented milks have been proposed by the International Dairy Federation (Hargrove and Alford 1974). Typical analyses of various fermented milks, as well as of their condensed and dried counterparts, are given in Table 2.4. 

Cultured buttermilk is manufactured by fermenting whole milk, reconstituted nonfat dry milk, partly skimmed milk, or skim milk with lactic acid bacteria. Most commercial cultured buttermilk is made from skim milk. Mixed strains of lactic streptococci are used to produce lactic acid and leuconostocs for development of the characteristic diacetyl flavor and aroma. Buttermilk is similar to skim milk in composition, except that it contains about 0.9% total acid expressed as lactic acid. The percentage of lactose normally found in skim milk is reduced in proportion to the percentage of lactic acid in the buttermilk. According to White (1978), the fat content of buttermilk usually varies from 1 to 1.8%, sometimes in the form of small flakes or granules to simulate churned buttermilk, the by-product of butter churning. Usually 0.1% salt is added. 

Vitamins and Minerals. Milk is a rich source of vitamins and other organic substances that stimulate microbial growth. Niacin, biotin, and pantothenic acid are required for growth by lactic streptococci (Reiter and Oram 1962). Thus the presence of an ample quantity of B-complex vitamins makes milk an excellent growth medium for these and other lactic acid bacteria. Milk is also a good source of orotic acid, a metabolic precursor of the pyrimidines required for nucleic acid synthesis. Fermentation can either increase or decrease the vitamin content of milk products (Deeth and Tamime 1981 Reddy et al. 1976). The folic acid and vitamin Bi2 content of cultured milk depends on the species and strain of culture used and the incubation conditions (Rao et al. 1984). When mixed cultures are used, excretion of B-complex vita-... 

In the current industrial process, nisin is manufactured by fermentation of L. lactis subsp. lactis in a milk-based medium. Biosynthesis of nisin is coupled with the growth of lactic acid bacteria and the production of a significant amount of lactic acid (7). Lactic acid is an important chemical for food processing. It can also be used as a raw material in the production of the biodegradable polymer poly(lactic) acid (12). Unfortunately, lactic acid is not recovered in the current nisin process. 

The Finnish fermented milk drink Evolus is fermented with a L. helveticus strain and contains the same tripeptides as Calpis . The Evolus drink has been demonstrated to exert a significant reduction in blood pressure of mildly hypertensive human subjects upon daily intake of 150 ml during a 21-week intervention period (Seppo et al., 2003). A fermented low-fat hard cheese Festivo was developed in Finland (Ryhanen et al., 2001) with probiotic lactic acid bacteria and was found to produce during maturation, high amounts of ACE-inhibitory peptides derived from asi-casein. The peptides emerged at the age of three months and their level remained rather stable at least for six months. 

The flavor of the cream may be enhanced by culturing, adding food-grade lactic acid bacteria, or adding natural flavors obtained by distilling a fermented milk cream may also be added to the finished butter. In addition, color, derived from an FDA-approved source, may be used (61). 

Lactic acid bacteria are used to produce fermented milk products, and the exopolysaccharides produced by the bacteria influence the texture of the resulting products. More importantly, these exopolysaccharides are thought to have several health benefits. There is evidence they lower cholesterol, modulate the immune system, help prevent colon cancer, and fight ulcers [342,343]. There is thus interest in establishing stmcture-function relationships for these stmctures, as well as in metabolic engineering of lactic acid bacteria to produce capsular polysaccharides with the desired properties [342,343]. 

Lactic acid bacteria and bifidobacteria are preferred as protective and probiotic cultures, and have been used since the beginning of history as starter cultures. They have a long history of being safely used and consumed. LAB are widely used for fermentation of milk, meat, and vegetable foods. In fermentation of dairy products, lactose is metabolized to lactic acid. Other metabolic products, hydrogen peroxide, diacetyl, and bacteriocins may also play inhibitory roles and contribute to improving the organoleptic attributes of these foods, as well as their preservation (Messens and De Vuyst, 2002). 

Martini, M.C., Lerebours, E.C., Lin, W., and Harlander, S.K. Strains and species of lactic acid bacteria in fermented milks (yoghurts) effect on in vivo lactose digestion. Am. J. Clin. Nutr., 54,1041,1991. 

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