Hemicelluloses negatively affect lignocellulose crystallinity for high biomass digestibility under NaOH and H2SO4 pretreatments in Miscanthus

Abstract

BackgroundLignocellulose is the most abundant biomass on earth. However, biomass recalcitrance has become a major factor affecting biofuel production. Although cellulose crystallinity significantly influences biomass saccharification, little is known about the impact of three major wall polymers on cellulose crystallization. In this study, we selected six typical pairs of Miscanthus samples that presented different cell wall compositions, and then compared their cellulose crystallinity and biomass digestibility after various chemical pretreatments.ResultsA Miscanthus sample with a high hemicelluloses level was determined to have a relatively low cellulose crystallinity index (CrI) and enhanced biomass digestibility at similar rates after pretreatments of NaOH and H2SO4 with three concentrations. By contrast, a Miscanthus sample with a high cellulose or lignin level showed increased CrI and low biomass saccharification, particularly after H2SO4 pretreatment. Correlation analysis revealed that the cellulose CrI negatively affected biomass digestion. Increased hemicelluloses level by 25% or decreased cellulose and lignin contents by 31% and 37% were also found to result in increased hexose yields by 1.3-times to 2.2-times released from enzymatic hydrolysis after NaOH or H2SO4 pretreatments. The findings indicated that hemicelluloses were the dominant and positive factor, whereas cellulose and lignin had synergistic and negative effects on biomass digestibility.ConclusionsUsing six pairs of Miscanthus samples with different cell wall compositions, hemicelluloses were revealed to be the dominant factor that positively determined biomass digestibility after pretreatments with NaOH or H2SO4 by negatively affecting cellulose crystallinity. The results suggested potential approaches to the genetic modifications of bioenergy crops.

Transformation of Miscanthus and Sorghum cellulose during methane fermentation

“…Mean values (n = 4) ± standard deviations; identical superscripts (a, b, c…) denote no significant difference (p \ 0.05) between mean values in rows according to Tukey's HSD test (ANOVA) for the investigated treatment options Crystallinity index of cellulose of the investigated varieties changes in the range from 54 to 64%, whereas a lower value below 60% was indicated for varieties of Sorghum harvested in both seasons for plant growing. Thus, taking into account that cellulose crystallinity negatively affected biomass digestion (Xu et al 2012), the feedstock which should undergo fermentation more easily is Sorghum. In the most of investigated cases there were no differences between crystallinity of cellulose of the plants harvested during and after the growing season and this implies that the structure was shaped at the beginning of the vegetation process.…”

Advances in Genetic Manipulation of Lignocellulose to Reduce Biomass Recalcitrance and Enhance Biofuel Production in Bioenergy Crops

“…Alkaline pretreatment using NaOH usually extracts more lignin than acid pretreatment using HCl and H 2 SO 4 by disassociating hydrogen and other covalent bonds with cellulose microfibrils, while acid pretreatment often gives higher wall polymers by splitting strong chemical bonds under high temperatures [116,118,119]. Besides, alkali-based pretreatment at high temperatures had minor impact on biomass digestibility, but at the low temperatures could lead to much higher biomass digestibility, compared to acid pretreatment executed in the biomass samples [120][121][122]. Additionally, both acid and alkaline pretreatments removed almost all carboxylic acid substitutions such as acetyl groups and uronic acids [120].…”

“…Lately, ionic liquid (IL) is also known as one of the most favorable pretreatment which can solubilize and separate cellulose from other plant cell wall efficiently at mild temperature [121][122][123][124][125]. [126].…”

Comparative Analysis of Enzymatic Hydrolysis of Miscanthus Xylan using Aspergillus niger, Hypocrea orientalis, and Trichoderma reesei Xylan-degrading Enzymes

“…Miscanthus with high biomass yield and low nitrogen and water requirement is considered as one of leading feedstocks for biofuel and value-added chemicals production (Xu et al 2012;Li et al 2013a). The aim of this work was to investigate the application potential of xylan-degrading enzymes from A. niger BE-2 and Hypocrea orientalis EU7-22 for the bioconversion of Miscanthus into monosaccharides and XOS.…”

“…Hemicelluloses play an important role in biomass enzymatic digestion (Xu et al 2012;Zhang et al 2012;Li et al 2013a). Xylan, the major hemicellulosic polysaccharide present in plant cell walls, has a backbone of β-1,4-linked xylose residues and side chains of different substituents (Vázquez et al 2002).…”