Optimization of d-lactic acid production by Lactobacillus coryniformis using response surface methodology Original Research Article

New low-cost media for lactic acid fermentation are desired to enhance the economics of the d-lactic acid production by Lactobacillus coryniformis. The aim of this work was to optimize the production of d-lactic acid from glucose by L. coryniformis in a reduced nutritional medium composed of corn steep liquors (CSL), yeast extract (YE) and peptone (P). Response surface methodology has been successfully used to modelling and optimizes the d-lactic acid production at variable fermentation times (20, 31, 44, 53, 72 and 96 h). The models predicted a maximum d-lactic acid concentration (58.9 g/l) at 96 h using 5 g CSL/l, 3.6 g YE/l and 10 g P/l. However, the maximum economic yield (10.14 $/$) was obtained at 96 h using 5 g CSL/l as a sole nutrient and the maximum economic productivity (0.22 $/h$) was obtained by reducing the fermentation time at 44 h.