Abstract: A strain, LB-103, which is capable of producing high concentration of L-lactic acid with high optical purity was isolated from kimchi. The optical purity of the produced lactic acid was measured to be 100% by using L-/D-lactic acid enzymatic test kit. The strain was identified as Lactobacillus rhamnosus based on its morphological features, physiological and biochemical properties (VITEK 2 automated microbial identification system), and 16S rDNA sequence analysis. It was named L. rhamnosus DLF-15038. Then the fermentation medium for L-lactic acid production was optimized, and the results showed that yeast extract (10 g/L) and cottonseed meal (15 g/L) were used as nitrogen sources to maintain high L-lactic acid yield and simultaneously reduce the cost. The optimal concentrations of inorganic salts in the medium were as follows: CH3COONa 3 g/L, KH2PO4 2 g/L, MnSO4 0.3 g/L and MgSO4 0.2 g/L. Finally, fed-batch fermentation was performed under the optimized conditions in a 5-L fermentor. We obtained 165.15 g/L L-lactic acid after 72 h fermentation by using the strain DLF-15038, with a yield of 93.34% (g L-lactic acid/g glucose), and a productivity of 2.29 g/(L·h).

Key words: L-lactic acid, Lactobacillus rhamnosus, isolation, identification, cottonseed meal