Abstract:

Lactococcus lactis KLDS 4.0325, a strain isolated from home-made koumiss in Xinjiang, China, was studied for
L-lactic acid production. The optical purity of the produced lactic acid was estimated to be 100% L-lactic acid using L/D-lactic
acid enzymatic test kit. The Plackett-Burman design was used to evaluate the effects of medium components on lactate
production. On the basis of statistical regression analysis, yeast extract, sucrose and K2HPO4 were found to be the most
important factors. Subsequently, response surface methodology was employed to determine the maximum lactate production
at the optimum concentrations of key factors. The lactate production was found to correlate to the three parameters. The
optimal levels of medium components were determined as 2.5 g/L yeast extract, 102.9 g/L srucose and 7.9 g/L K2HPO4. The
predicted yield of lactate using the optimized medium was 86.3 g/L, and the actual experimental result was 86.6 g/L.

Key words: L-lactate, optical purity, Lactococcus lactis KLDS 4.0325, response surface methodology