High-efficient L-lactic acid production from inedible starchy biomass by one-step open fermentation using thermotolerant Lactobacillus rhamnosus DUT1908.

The purpose of this study was to establish a simplified operational process for lactic acid (LA) production from inedible starchy biomass by open fermentation using thermotolerant Lactobacillus rhamnosus DUT1908. One step simultaneous liquefaction, saccharification and fermentation (SLSF) was proposed to produce LA using aging paddy rice with hull (APRH) as feedstock. First, a robust microbial strain was obtained by adaptive laboratory evolution under high temperature stress. As a result, L. rhamnosus DUT1908 showed high thermotolerance up to 50 °C and high efficiency of substrate utilization. Then, the performance of this thermotolerant L-lactic acid producing strain was demonstrated. Finally, various fermentation strategies were compared for LA production from APRH, including simultaneous saccharification and fermentation (SSF) and SLSF. In one-step open SLSF process, 107.8 g/L lactic acid was obtained with a productivity of 3.4 g/(L.h) and a yield to theoretical glucose of 0.89 g/g. This is the highest yield and productivity of lactic acid reported on starchy residues, and provides an efficient route for the development of high value-added products.