Ethanol production from alfalfa fiber fractions by saccharification and fermentation

This work describes ethanol production from alfalfa fiber using separate hy drolysis and fermentation (SHF) and simultaneous saccharification and ferme ntation (SSF) with and without liquid hot water (LHW) pretreatment. Candida shehatae FPL-702 produced 5 and 6.4 g/l ethanol with a yield of 0.25 and 0 .16 g ethanol/g sugar respectively by SHF and SSF from alfalfa fiber withou t pretreatment. With LHW pretreatment using SSF, C. shehatae FPL-702 produc ed 18.0 g/l ethanol, a yield of 0.45 g ethanol/g sugar from cellulosic soli ds or 'raffinate'. Using SHF, it produced 9.6 g/l ethanol, a yield of 0.47 g ethanol/g sugar from raffinate. However, the soluble extract fraction con taining hemicelluloses was poorly fermented in both SHF and SSF due to the presence of inhibitors. Addition of dilute acid during LHW pretreatment of alfalfa fiber resulted in fractions that were poorly saccharified and ferme nted. These results show that unpretreated alfalfa fiber produced a lower e thanol yield. Although LHW pretreatment can increase ethanol production fro m raffinate fiber fractions, it does not increase production from the hemic ellulosic and pectin fractions. (C) 2001 Elsevier Science Ltd. All rights r eserved.