Microorganisms have been used to produce food for thousands of years. Yogurt, cheese, pickled vegetables, and other fermented foods are not only perceived as pleasant tasting, but the acids produced as a by-product of microbial metabolism inhibit the growth ofmany spoilage organisms as well as foodborne pathogens. Thus, fermentation historically has been, and continues to be today, an important method of food preservation, particularly when modern conveniences such as refrigeration are lacking.
The development of methods for isolating and culturing microorganisms has enabled the scientific study of the micro-bial processes involved in the production of fermented foods. In turn, this has resulted in changes, such as the careful selection of microbial strains, that have increased the efficiency of production and/or the quality of fermented food products. Nevertheless, some ancient processes, including the production of some fine cheeses and wines, are not fully understood, and still remain somewhat of an art.
Lactic Acid Fermentations by the Lactic Acid Bacteria
The tart taste of yogurt, pickles, sharp cheeses, some sausages, and other foods is due to the production of lactic acid by one or more members of a group of bacteria known as the lactic acid bacteria (table 32.1). This group of organisms, including members of the genera Lactobacillus, Lactococcus, Streptococcus, Leuconostoc, and Pediococcus, are obligate fermenters that characteristically produce lactic acid as an end product of their metabolism. Some also produce flavorful and aromatic compounds that contribute to the overall quality of fermented foods. ■ lactic acid bacteria, p. 275 ■ obligate fermenters, pp. 89,151
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