Surface properties correlate to the digestibility of hydrothermally pretreated lignocellulosic Poaceae biomass feedstocks

Abstract

BackgroundUnderstanding factors that govern lignocellulosic biomass recalcitrance is a prerequisite for designing efficient 2nd generation biorefining processes. However, the reasons and mechanisms responsible for quantitative differences in enzymatic digestibility of various biomass feedstocks in response to hydrothermal pretreatment at different severities are still not sufficiently understood.ResultsPotentially important lignocellulosic feedstocks for biorefining, corn stover (Zea mays subsp. mays L.), stalks of Miscanthus × giganteus, and wheat straw (Triticum aestivum L.) were systematically hydrothermally pretreated; each at three different severities of 3.65, 3.83, and 3.97, respectively, and the enzymatic digestibility was assessed. Pretreated samples of Miscanthus × giganteus stalks were the least digestible among the biomass feedstocks producing ~24 to 66.6% lower glucose yields than the other feedstocks depending on pretreatment severity and enzyme dosage. Bulk biomass composition analyses, 2D nuclear magnetic resonance, and comprehensive microarray polymer profiling were not able to explain the observed differences in recalcitrance among the pretreated feedstocks. However, methods characterizing physical and chemical features of the biomass surfaces, specifically contact angle measurements (wettability) and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy (surface biopolymer composition) produced data correlating pretreatment severity and enzymatic digestibility, and they also revealed differences that correlated to enzymatic glucose yield responses among the three different biomass types.ConclusionThe study revealed that to a large extent, factors related to physico-chemical surface properties, namely surface wettability as assessed by contact angle measurements and surface content of hemicellulose, lignin, and wax as assessed by ATR-FTIR rather than bulk biomass chemical composition correlated to the recalcitrance of the tested biomass types. The data provide new insight into how hydrothermal pretreatment severity affects surface properties of key Poaceae lignocellulosic biomass and may help design new approaches to overcome biomass recalcitrance.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-017-0730-3) contains supplementary material, which is available to authorized users.

Effects of preheating on briquetting and subsequent hydrothermal pretreatment for enzymatic saccharification of wheat straw

“…The chemical composition of un‐briquetted WS and briquettes, before and after pretreatment, is reported in Table . The glucan, xylan, arabinan, and lignin contents of unpretreated and pretreated WS were comparable with a previous study . The composition of WS and briquettes was similar, which indicated that briquetting with or without preheating had no significant effects on measured macromolecular chemical composition.…”

“…The glucan, xylan, arabinan, and lignin contents of unpretreated and pretreated WS were comparable with a previous study. 25 The composition of WS and briquettes was similar, which indicated that briquetting with or without preheating had no significant effects on measured macromolecular chemical composition. Previous studies also reported that densification (pelletization) has no significant effect on the composition of biomass.…”

“…The absorbance band at 895 cm −1 representing anomeric carbon‐groups, carbon 1‐hydrogen deformation, and ring valence vibration was assigned to holocellulose . The band at 1,508 cm −1 representing aromatic skeletal vibrations was assigned to lignin and the band at 1,732 cm −1 was assigned to hemicellulose . Ratios of peak areas were calculated for 1,508/895 cm −1 corresponding to lignin/holocellulose (L/HC) and 1,732/895 cm −1 corresponding to hemicellulose/holocellulose (H/HC) for semiquantitative analysis of the biopolymer composition.…”

Cellulases adsorb reversibly on biomass lignin

“…LRRs were obtained from extensive enzymatic hydrolysis of hydrothermally pretreated spruce (HPS) and wheat straw (HPWS) followed by protease treatment optimized from a previous method (Rahikainen et al, ). The hydrothermal pretreatment conditions were 195°C for 15 min (log R 0 = 3.97) for wheat straw (Djajadi et al, ) and 200°C for 10 min (log R 0 = 3.94) for spruce. The composition of the LRRs have been determined using the National Renewable Energy Laboratory protocol (Sluiter et al, ).…”

“…LRRs were obtained from extensive enzymatic hydrolysis of hydrothermally pretreated spruce (HPS) and wheat straw (HPWS) followed by protease treatment optimized from a previous method (Rahikainen et al, 2011). The hydrothermal pretreatment conditions were 195°C for 15 min (log R 0 = 3.97) for wheat straw (Djajadi et al, 2017) and…”