Effective lactic acid production by two-stage extractive fermentation

For effective microbial lactic acid production using Lactobacillus delbrueckii, two-stage extractive fermentation was examined. Extractants were screened from the viewpoints of a high distribution coefficient for lactic acid and less toxicity toward the microorganism. Even if the extractant showed some toxicity toward the microorganism, it was found that a reduction of toxicity was possible by back-extraction using oleyl alcohol. As a result, 40% Alamine 336 diluted with oleyl alcohol, and oleyl alcohol, were selected as the extractant and the back-extractant, respectively. After two-stage extraction by these extractants, the growth rate was improved by the removal of lactic acid. This method was then applied to continuous extractive fermentation using a jar-fermentor. During 4-h extraction, lactic acid accumulation in the broth was significantly suppressed, while the cell growth and glucose consumption rates were also found not to be reduced. After 24 h, the cell concentration attained an OD₆₆₀ of 14, which corresponded to a level 1.25 times higher than that of the control culture without extraction. Total lactic acid productivity was 1.4 times level compared with the control culture.