Production of lactic acid from lignocellulose in a single stage of hydrolysis and fermentation

Samples of a model lignocellulosic substrate (wood subjected to treatments of delignification and swelling) were hydrolyzed and fermented in a single stage to obtain lactic acid. The hydrolysis stage was carried out using commercial cellulases with or without addition of fresh cellobiase, and Lactobacillus delbrueckii NRRL B-445 was used for converting both glucose and cellobiose into lactic acid. Assays were performed starting the hydrolysis and fermentation stages at the same time (Simultaneous Saccharification and Fermentation, SSF) or inoculating hydrolysis media partially saccharified (Combined Hydrolysis and Fermentation, CHF). Both glucose and cellobiose were rapidly depleted by microorganisms, showing a kinetic pattern governed by the hydrolysis stage. The effect of selected operational variables (enzyme loading, substrate concentration and duration of the process) was explored. Under the best conditions assayed, lactic acid concentrations in the vicinity of 30 g/L were reached in experiments lasting 40-60 hours.