Deacetylation kinetics of promising energy crops, hemp and kenaf, for cellulosic ethanol production

Abstract

Lignocellulosic hydrolysates contain acetic acid derived from hemicellulose. Acetate released during acid pretreatment interferes with enzymatic saccharification of the biomass and inhibits yeast fermentation, caused by cellular oxidation and stress. This study used alkaline deacetylation prior to acid pretreatment and evaluated its influence on the fermentation performance of Saccharomyces cerevisiae using two different lignocellulosic biomasses, hemp (Cannabis sativa) and kenaf (Hibiscus cannabinus). They are valuable for biofuel production. The maximal acetate removal with minimal sugar loss was obtained with 1% (w/v) NaOH treatment for both biomasses. Deacetylation pretreatment under this condition was effective both in enzymatic saccharification and simultaneous saccharification and fermentation. This resulted in improved ethanol production by xylose-consuming yeast (S. cerevisiae SR8) by removing 4.7 g/L of acetate from hemp and 6.3 g/L from kenaf, thus resulting in the ethanol productivities of 0.79 and 0.67 g/L-h from hemp and kenaf, respectively. This suggests that strategies to overcome acetate inhibition are necessary to efficiently use the lignocellulosic biomass as a source for bioenergy production.