L-lactic acid production by simultaneous saccharification and fermentation of dilute ethylediamine pre-treated rice straw

Abstract

To effectively produce second-generation L-lactic acid (L-LA), for the first time, rice straw (RS) was pretreated by dilute ethylenediamine (EDA) and followed by fed-batch simultaneous saccharification and fermentation (SSF) under non-sterilized conditions. Specifically, the impact of pretreatment parameters included EDA concentration and pretreatment temperature on sugars and L-LA productions were evaluated. Results indicated that after pretreatment in 6% (w/v) EDA at 200 °C for 1 h and following the enzymatic hydrolysis, 42.25 g L−1 of total monomer sugars was generated. By batch SSF, the maximized 63.5 ± 3.0 g L−1and 296.8 g Kg−1 of L-LA can be obtained from the raw RS using Bacillus coagulans LA-15-2. Fed-batch SSF was further conducted and L-LA concentration of 92.5 g L−1 was obtained in the final fermentation broth. Correspondingly, L-LA productivity and yield reached 2.01 g L−1 h−1 and 578.1 g Kg−1of the pretreated RS, respectively. This study provided a novel environmental-friendly method for L-LA production, which successfully avoided the usage of large amount of inorganic alkali in lignocellulose pretreatment stage.