High-Titer L-lactic Acid Production by Fed-Batch Simultaneous Saccharification and Fermentation of Steam-Exploded Corn Stover

Steam explosion (SE) is an effective lignocellulose pretreatment technology for second-generation L-lactic acid (L-LA) production. In this study, targeted to produce high-concentration L-LA from corn stover (CS), the fed-batch simultaneous saccharification and fermentation (SSF) of acidic, SE-pretreated CS was developed and demonstrated in a 5 L scale bioreactor under non-strict conditions (without detoxification and sterilization). The results indicated that the fed-batch SSF, with a simple pH control, realized a higher tolerance of the strains to the toxic by-products of hydrolysate, in comparison to the conventional sequential hydrolysis and fermentation (SHF), allowing for 153.8 g L−1 of L-LA production, along with a productivity of 1.83 g L−1 h−1 in a system with a total of 40% (w/v) solid loading. The mass balance indicated that up to 449 kg of L-LA can be obtained from 1 t of dried CS. It exhibited obvious superiorities and laid down a solid foundation for the industrialization of second-generation L-LA production.