Statistical optimization of cassava starch medium for D-lactic acid production using Leuconostoc mesenteroides ZL01

The purpose of this study was to investigate a D-lactic acid production process from cassava with high optical purity, high yield, and without by-products. In order to improve the lactic acid production capability of L. mesenteroides ZL01, the Plackett-Burman and Box-Behnken Design with Response Surface Methodology approach were employed to optimize the media composition. The lactic acid concentration in shake flask fermentation was 35.51 g/L using the optimized medium, which increased the production by 54.1% compared to 23.04 g/L using the unoptimized medium. In a 3-liter stirred bioreactor, substrate inhibition and product inhibition effects were found in the L. mesenteroides ZL01 lactic acid production using glucose as carbon sources. However, the use of cassava starch hydrolysate as a raw material can alleviate these two inhibitory effects. The inhibition of substrate was alleviated by fed-batch fermentation and the inhibition of lactic acid was alleviated by adjusting pH during fermentation, which further improved the production of lactic acid. Under the optimal fermentation process, 136.2 g/L lactic acid was produced with a yield of 1 g/g. This is the highest D-lactic acid concentration reported from L. mesenteroides fermentation, which provides a promising pathway for the production of D-lactic acid from cassava.