LACTIC ACID BACTERIA
1969; Elsevier BV; Linguagem: Inglês
10.1016/b978-1-4832-3135-8.50011-4
Autores Tópico(s)Probiotics and Fermented Foods
ResumoThis chapter presents the lactic acid bacteria that are represented by species of the Lactobacillaceae, which are well-known spoilage organisms in food such as dairy products. They are morphologically a heterogeneous group and are biochemically characterized by their main end product, lactic acid. These organisms are gram-positive, nonsporulating cocci or rods. Some are catalase positive and some catalase negative. A characteristic feature of the lactic acid produced by the Lactobacillaceae is that the optical activity of the acid depends upon the strain of organism. Two factors appear to be responsible for this final activity: (1) the stereospecificity of the lactate dehydrogenase involved and (2) the presence or the absence of a lactate racemase. In the lactic acid bacteria, energy can also be derived by citrate metabolism in the absence of carbohydrate fermentation or lactate production. The balance of products is markedly dependent upon pH. If the pH increases, more acetate and formate are obtained at the expense of lactate and carbon dioxide. The first step of citrate fermentation is the formation of pyruvate. The degradation of pyruvate is markedly pH-dependent. In the lactic acid bacteria, the fermentation of hexonic acids resembles the fermentation of glucose.
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