Strategies to improve the bioconversion of processed wood into lactic acid by simultaneous saccharification and fermentation

In the one-step conversion of wood into lactic acid by Simultaneous Saccharification and Fermentation (SSF), inhibition effects caused by hydrolysis- and fermentation-derived compounds on both enzymatic activity and fermentative ability of microorganisms appear when the operation is carried out under conditions leading to high productivities. The main effects inhibiting SSF have been assessed, and the results obtained in fed-batch experiments allowed the definition of strategies for improving the overall bioconversion process. As cellobiose caused significant inhibition of cellulases, the supplementation of media with beta -glucosidase resulted in improved kinetics and yields. The inhibition of both enzymatic activity and microbial metabolism by lactic acid was confirmed. Intermittent removal of lactic acid by passing the fermentation media through an anion-exchange resin column resulted in increased productivities and yields. Improved conversion of pretreated wood into lactic acid (67% conversion of cellulose into lactic acid, with maximum lactic acid concentration of 108g dm(-3) and a productivity of 0.94g dm(-3)h(-1)) was achieved combining multiple substrate addition, supplementation with fresh nutrients and enzymes and removal of lactic acid. (C) 2001 Society of Chemical Industry.