Efficient open integrated lactic acid fermentation of undetoxified semi-hydrolysate of rice straw using thermophilic Enterococcus faecium QU 50

Lactic acid fermentation using lignocellulosic substrates has attracted massive interest. However, it encountered several problems, including high enzyme cost, inhibitors generated in pretreatment, carbon catabolite repression (CCR). In this work, we constructed open lactic acid fermentation of undetoxified hydrolysate of rice straw using thermophilic Enterococcus faecium QU 50. The lactic acid yield to enzyme loading was improved from 0.00500 g/U to 0.125 g/U by 2400% when semi-hydrolysate, produced by low enzyme loading, was used. The yield was further improved by 106% via recycling enzymes in repeated simultaneous saccharification and co-fermentation (RSScF). Furthermore, the overall productivity of lactic acid was increased by 16.4% in simultaneously repeated hydrolysis and fermentation (SRHF). Thus, this work provided a promising way to eliminate the defects of lactic acid fermentation from lignocellulose.