Response surface optimization of D(-)-lactic acid production by Lactobacillus SMI8 using corn steep liquor and yeast autolysate as an alternative nitrogen source

The production of D(-) lactic acid from Lactobacillus LMI8 sp. was studied, using 2 low-cost nitrogen sources: corn steep liquor (CSL) and yeast autolysate (YA). A central composite design was used to determine maximal lactic acid production. The surface response method was used to evaluate the results of the experiments. The assays were performed in 250 mL Erlenmeyer flasks containing 100 mL of production medium maintained under refrigerated incubation at 200 rpm and a temperature of 37 ± 1°C for 48 h of fermentation. Lactic acid production was significantly affected by the isolated CSL as well as the interaction between CSL and YA. Maximal production of D(+) lactic acid was 41.42 g/L – a value located at the central point, which corresponded to 15 g/L of CSL and 5 g/L of YA. Key words: D(-)-Lactic acid, Lactobacillus, corn steep liquor, yeast autolysate, response surface methodology, medium optimization.