Production of optically pure l(+)-lactic acid from various carbohydrates by batch fermentation of Enterococcus faecalis RKY1

Abstract

Lactic acid fermentations from various carbohydrates using Enterococcus faecalis RKY1 were investigated. Galactose was metabolized into formic and acetic acids as major products, whereas xylose, glycerol, whey, and starch were poorly utilized. When the cells were grown on fermentation medium containing glucose, fructose, and maltose, they produced lactic acid with a high yield through homofermentative pathway. During lactic acid fermentation with glucose, fructose, or maltose as a carbon source, the average volumetric productivities ranged between 5.2 and 6.0 g/l h −1 with the lactic acid yield of 0.96 g lactic acid/g carbon source. In addition, lactic acid produced from glucose, fructose, and maltose by E. faecalis RKY1 was almost optically pure l(+)-lactic acid (over 99% of total lactic acid produced). Therefore, E. faecalis RKY1 was found to be the excellent lactic acid bacterium for the production of optically pure l(+)-lactic acid with a high yield through the homofermentative pathway.