Multimodal analysis of pretreated biomass species highlights generic markers of lignocellulose recalcitrance

Abstract

BackgroundBiomass recalcitrance to enzymatic hydrolysis has been assigned to several structural and chemical factors. However, their relative importance remains challenging to evaluate. Three representative biomass species (wheat straw, poplar and miscanthus) were submitted to four standard pretreatments (dilute acid, hot water, ionic liquid and sodium chlorite) in order to generate a set of contrasted samples. A large array of techniques, including wet chemistry analysis, porosity measurements using NMR spectroscopy, electron and fluorescence microscopy, were used in order to determine possible generic factors of biomass recalcitrance.ResultsThe pretreatment conditions selected allowed obtaining samples displaying different susceptibility to enzymatic hydrolysis (from 3 up to 98% of the initial glucose content released after 96 h of saccharification). Generic correlation coefficients were calculated between the measured chemical and structural features and the final saccharification rates. Increases in porosity displayed overall strong positive correlations with saccharification efficiency, but different porosity ranges were concerned depending on the considered biomass. Lignin-related factors displayed highly negative coefficients for all biomasses. Lignin content, which is likely involved in the correlations observed for porosity, was less detrimental to enzymatic hydrolysis than lignin composition. Lignin influence was highlighted by the strong negative correlation with fluorescence intensity which mainly originates from monolignols in mature tissues.ConclusionsOur results provide a better understanding of the factors responsible for biomass recalcitrance that can reasonably be considered as generic. The correlations with specific porosity ranges are biomass species-dependent, meaning that enzymes cocktails with fitted enzyme size are likely to be needed to optimise saccharification depending on the biomass origin. Lignin composition, which probably influences its structure, is the most important parameter to overcome to enhance enzymes access to the polysaccharides. Accordingly, fluorescence intensity was found to be a rapid and simple method to assess recalcitrance after pretreatment.Electronic supplementary materialThe online version of this article (10.1186/s13068-018-1053-8) contains supplementary material, which is available to authorised users.

Low-Cost Cellulase-Hemicellulase Mixture Secreted by Trichoderma harzianum EM0925 with Complete Saccharification Efficacy of Lignocellulose

“…So, the enzyme cocktail EM0925 was much more effective than the current commercial products under the conditions tested, since only 46.9% sugar yield was acquired from UGCS by Celluclast 1.5 L after 72 h hydrolysis [33] (Table S1). In general, saccharification efficiency of lignocellulose biomass by EM0925 was better than that in any other literature reported under the conditions tested [29][30][31][32][33][34]. To be specific, in our study, the maximum 85.59% glucose yield and 66.18% xylose yield were obtained from UGCS hydrolyzed with 30 FPU/g of Celluclast 1.5 L used; while 100% glucose yield and 100% xylose yield were obtained from UGCS and ALKCS with the same enzyme dosage of T. harzianum EM0925.…”

“…Monosaccharides yield was 865.5 mg/g of UGCS and 1073 mg/g of ALKCS, which was 1.29 and 1.31-fold of the highest monosaccharide yield obtained by Celluclast 1.5 L. In addition, the highest sugar yield from UGCS was obtained when EM0925 was applied at the dosage corresponding to 1/6 of the Celluclast 1.5 L dose (Figure 6a,b). These saccharification yields are among the highest yields reported in literature [29][30][31][32][33][34] (Table S1).…”

Lignocellulosic Biomass: Understanding Recalcitrance and Predicting Hydrolysis

“…Hemicelluloses act as a physical barrier limiting the accessibility of enzymes. It has been reported that removal of hemicelluloses by dilute acid or steam explosion pre-treatment could increase cellulose conversion by improving the accessibility of enzymes to cellulose (Auxenfans et al, 2017a;Herbaut et al, 2018;Santos et al, 2018). Kruyeniski et al (2019) reported that the removal of hemicelluloses on pre-treated pine improved the fibers porosity and the area available for enzymes.…”

“…Also, it can irreversibly adsorb cellulases and other enzymes during enzymatic hydrolysis due to its hydrophobic structural features including hydrogen bonding, methoxy groups, and polyaromatic structures (Kumar and Wyman, 2009b;Zeng et al, 2014). Previous studies showed that the lignin content was negatively correlated with enzymatic digestibility in poplar (Meng et al, 2017;Yoo et al, 2017a), also in miscanthus, in wheat straw (Herbaut et al, 2018) and in transgenic rice (Huang et al, 2017). The removal of lignin generally disrupts the lignincarbohydrates matrix, increases the porosity and reduces nonproductive adsorption sites for enzymes (Pihlajaniemi et al, 2016;Kruyeniski et al, 2019).…”

Analytical Enzymatic Saccharification of Lignocellulosic Biomass for Conversion to Biofuels and Bio-Based Chemicals

“…The interference by lignin and hemicelluloses, which are intimately associated with cellulose fibrils in the lignocellulosic matrix, is a major factor contributing to the biomass recalcitrance. Although lignin content has been considered to be one of the main obstacles for cellulose enzymatic hydrolysis, a recent report points towards a more crucial role of lignin composition, in particular the content of syringyl and guaiacyl units and the amount of aryl ether linkages, as a key impediment for access of enzymes to the polysaccharides [18]. The capacity of lignin and pseudo-lignin, a product of carbohydrate degradation during thermal processing, to non-productively bind cellulases is another factor contributing to biomass recalcitrance [19].…”