Effective D-lactic acid production from corncobs by simultaneous saccharification and fermentation using metabolically engineered Lactobacillus plantarum

A metabolically engineered Lactobacillus plantarum mutant, which could produce D-lactic acid from both glucose and xylose, was applied for the production of optically pure D-lactic acid from corncobs by simultaneous saccharification and fermentation (SSF). Using a corncob hydrolysate obtained by a combination of dilute acid treatment using 1.5% H2SO4 followed by enzymatic saccharification, the L. plantarum mutant completely assimilated both glucose and xylose in the corncob hydrolysate within 20 hours, resulting in the successful production of D-lactic acid with high optical purity in a batch culture. To improve the performance of D-lactic acid production from corncobs, SSF experiments from 100 to 250 g/L of acid-hydrolyzed corncobs using 1.5% H2SO4 were performed, and 49.7 to 101 g/L of D-lactic acid with 96.8-98.6% of optical purity was successfully produced. The D-lactic acid yield from corncobs (YL/C) was approx. 0.61 when 100-150 g/L of acid-hydrolyzed corncobs was used; however, the YL/C decreased to 0.49 as the concentration of acid-hydrolyzed corncobs because of insufficient acid hydrolysis of the corncobs. Therefore, by increasing the H2SO4 concentration to 3.5%, D-lactic acid production from corncobs significantly increased to 134 g/L with YL/C of 0.63 and 2.88 g/(L･h) of productivity from 250 g/L of acid-hydrolyzed corncobs.

High yield of ethanol production by the strain Fusarium sp. ZW-21 with corncob hydrolysate

The filamentous fungus strain Fusarium sp. ZW-21 was used for ethanol production with corncob hydrolysate. The fermentation conditions of ethanol production from corncob hydrolysate by the strain were investigated, and the effect of temperature, pH, nitrogen source, and surfactants on the ethanol production was investigated. The two factors yeast extract and polysorbate 80 were selected for further optimization by response surface methodology. The optimal conditions for ethanol production by the strain Fusarium sp. ZW-21 were 50 g/L sugar of corncob hydrolysate, 10.35 g/L yeast extract, 10 g/L KH2PO4, 0.5 g/L MgSO4·7H2O, 0.38 g/L polysorbate 80, pH 6.0, inoculum size of 1 mL/50 mL medium, and incubation temperature of 30 °C. The fermentation period was 5 d under oxygen-limited conditions, and the ethanol yield was 24.2 g/L.