Hemicelluloses negatively affect lignocellulose crystallinity for high biomass digestibility under NaOH and H 2SO 4 pretreatments in Miscanthus

Abstract

Background: Lignocellulose is the most abundant biomass on earth. However, biomass recalcitrance has become amajor factor affecting biofuel production. Although cellulose crystallinity significantly influences biomasssaccharification, little is known about the impact of three major wall polymers on cellulose crystallization. In thisstudy, we selected six typical pairs of Miscanthus samples that presented different cell wall compositions, and thencompared their cellulose crystallinity and biomass digestibility after various chemical pretreatments.Results: A Miscanthus sample with a high hemicelluloses level was determined to have a relatively low cellulosecrystallinity index (CrI) and enhanced biomass digestibility at similar rates after pretreatments of NaOH and H2SO4with three concentrations. By contrast, a Miscanthus sample with a high cellulose or lignin level showed increasedCrI and low biomass saccharification, particularly after H2SO4 pretreatment. Correlation analysis revealed that thecellulose CrI negatively affected biomass digestion. Increased hemicelluloses level by 25% or decreased celluloseand lignin contents by 31% and 37% were also found to result in increased hexose yields by 1.3-times to 2.2-timesreleased from enzymatic hydrolysis after NaOH or H2SO4 pretreatments. The findings indicated that hemicelluloseswere the dominant and positive factor, whereas cellulose and lignin had synergistic and negative effects onbiomass digestibility.Conclusions: Using six pairs of Miscanthus samples with different cell wall compositions, hemicelluloses wererevealed to be the dominant factor that positively determined biomass digestibility after pretreatments with NaOHor H2SO4 by negatively affecting cellulose crystallinity. The results suggested potential approaches to the geneticmodifications of bioenergy crops. © 2012 Xu et al.; licensee BioMed Central Ltd.