The production of L(+) and D(−) lactic acid in cultures of some lactic acid bacteria, with a special study ofLactobacillus acidophilusNCDO 2

Summary A study of the production of L(+) and D(−) lactic acid in cultures of DL forming lactic acid bacteria has shown that they can be divided into 2 groups. The first includes the thermobacteria andPediococcus cerevisiaein which the percentage of L(+) lactic acid is high initially but decreases as the cultures grow. The second includesLactobacillus plantarumand the heterofermentative lactobacilli and in cultures of these species the percentage of L(+) acid changes little during growth and is generally below 50% of the total. In a strain ofLactobacillus acidophilusit has been found that if the pH is kept constant during growth the proportion of L(+) lactic acid decreased. However, when acid production stopped the proportion of total acid which is the L(+) isomer is greater than the proportion at the same stage of development in cultures where the pH was not adjusted. Cells harvested from young cultures formed more L(+) acid than cells harvested from older cultures. There is some evidence that the composition of the medium can affect the ratio of L(+):D(−) lactic acid.