Utilization of sugar molasses for economical l(+)-lactic acid production by batch fermentation of Enterococcus faecalis

Lactic acid production from sugar molasses by batch fermentation of Enterococcus faecalis RKY1 was investigated in order to reduce the manufacturing cost of lactic acid. When the fermentation was carried out at pH 7.0, 95.7 g/l of lactic acid was obtained with a yield of 94.9% and productivity of 4.0 g/l h. Lactic acid fermentation using molasses was significantly affected by yeast extract concentrations. The maximum lactic acid productivity was obtained to 5.3 g/l h at 20 g/l of yeast extract. The final lactic acid increased with the increase of molasses concentrations, whereas the lactic acid productivity decreased probably due to substrate inhibition. When the medium containing 15 g/l of yeast extract was used, the maximum lactic acid concentration (134.9 g/l) and the maximum productivity (4.3 g/l h) were obtained at molasses concentrations of 333 g/l (equivalent to 170 g/l of total sugar) and 130 g/l (equivalent to 68 g/l of total sugar), respectively. In addition, l(+)-lactic acid content of lactic acid produced from molasses was above 98% in all cases experimented in this study.