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Background: Humic acids (HA) have been used in biorefinery process due to its surfactant properties as an aid to the pretreatment of lignocellulose, with results indicating a positive effect on delignification. However, the HA remaining on the surface of the pretreated lignocellulose has also been shown to provide a negative effect on ensuing enzymatic digestibility. Hence, a strategy of complexing metallic cations with HA prior to enzymatic hydrolysis was proposed and demonstrated in this work in an effort to provide a means of HA mitigation that does not involve significant water consumption via extensive washing. Results: Results showed that the enzymatic hydrolysis efficiency of waste wheat straw decreased from 81.9% to 66.1% when it was pretreated by 10 g/L HA, attributed to the inhibition ability of the residual HA on enzyme activity of cellulase with a debasement of 36.3%. Interestingly, enzymatic hydrolysis efficiency could be increased from 66.1% to 77.3% when 10 mM Fe3+ was introduced to the system and allowed to associate with HA during saccharification. Conclusions: The addition of high-priced metallic cations (Fe3+) has successfully alleviated the effect of HA on cellulase activity. It is our hope in demonstrating the complexation affinity between metallic cations and HA, future researchers and biorefinery developers will evaluate this strategy as a unit operation that could allow economic biorefining of WWS to produce valuable biochemicals, biofuels, and biomaterials. [ABSTRACT FROM AUTHOR]

In this study, a novel biomass pretreatment process using three kinds of deep eutectic solvents (DESs) was developed to improve saccharification efficiency and lignin valorization. The major components of xylose residue including cellulose and lignin fractions were released, recovered and utilized. Pretreatment with betaine/lactic acid system at 120 °C for 2 h was found to be the optimal conditions with prominently increased enzymatic digestibility (from 55.3% to 96.8%). The efficient conversion was mainly ascribed to the significant delignification efficiency of 81.6% after betaine/lactic acid pretreatment, which caused incompact structure and corrosive surface of treated xylose residue. The recoverable lignin had high purity, low molecular weight (630–2040 g/mol) and polydispersity (1.07–1.76). Based on the comprehensive analysis, the one-pot DESs system provides us a facile and effective approach for whole components valorization of lignocellulosic materials. [ABSTRACT FROM AUTHOR]

Sole pretreatment methods always have limitations in improving enzymatic hydrolysis of wood due to the multi-scale biomass recalcitrance. Herein, dilute acid pretreatment (DAP) with 2% hydrochloric acid at 160 °C and mild ionic liquid pretreatment (MILP) with 1-ethyl-3-methylimidazolium acetate at 90 °C were combined to increase cellulose accessibility in poplar wood. Additionally, the compositional, structural, and topochemical changes of wood during pretreatment and their effect on cellulose digestibility were comprehensively investigated and well understood. The sequential DAP and then MILP led to the highest yield of fermentable sugar (87.15%) after 72 h enzymatic hydrolysis when compared with the sole pretreatments and the sequential MILP and then DAP (21.31–73.64%). We suggested that the significant hemicellulose removal and cell wall deconstruction during first-step DAP exposed more cellulose fibrils to ionic liquid, thereby improving the efficacy of subsequent MILP to delignify wood and change cellulose crystal structure. The considerable removal of both hemicellulose and lignin, the damage of wood structure, and the crystal transformation from cellulose I to cellulose II dramatically improved the enzymatic hydrolysis of the DA + MIL sample. This study provides a better understanding of decomposition mechanism of cell walls during DAP and MILP, which can offer valuable insights into the development of promising pretreatment strategies. [ABSTRACT FROM AUTHOR]

The study aimed to explore the crystallinity and crystalline structure of alkaline pretreated cellulose. The enzymatic hydrolysis followed by pretreatment was conducted for measuring the efficiency of sugar conversion. For cellulose Iβ dominated samples, alkaline pretreatment (<8 wt%) caused increased cellulose crystallinity and depolymerized hemicelluloses, that were superimposed to affect the enzymatic conversion to glucose. Varying crystallite sizes and lattice spacings indicated the separation of cellulose crystals during mercerization (8–12 wt% NaOH). Completion of mercerization was proved under higher alkaline concentration (14–18 wt% NaOH), leading to distortion of crystalline cellulose to some extent. Cellulose II crystallinity showed a stimulative impact on enzymatic hydrolysis due to the weakened hydrophobic interactions within cellulose chains. The current study may provide innovative explanations for enhanced enzymatic digestibility of alkaline pretreated lignocellulosic materials. [ABSTRACT FROM AUTHOR]

Developing green pretreatment technologies that prioritize the selective separation of lignin is of significant importance for the industrialization of biorefining. This work employed H 2 SO 4 -catalyzed γ-valerolactone (GVL) pretreatment on masson pine sawdust (GAM) to investigate process conditions and the enzymatic hydrolysis performance of masson pine. The results indicated that the lignin removal rate was 87.2% under the optimal pretreatment conditions (150ºC, 75 mM H 2 SO 4). The synergistic effect of the H 2 SO 4 catalyst and GVL pretreatment resulted in an enzymatic hydrolysis yield for GAM (76.8%) nearly six times higher than that of other non-synergistic systems (5.7%∼13.0%). Furthermore, the enzymatic hydrolysis yield increased to 97.3% upon the addition of bovine serum albumin. Microscopic visualization was used to analyze the morphological changes of cells and the micro-distribution of lignin within GAM cell walls after pretreatment. Additionally, structural changes in the molecular weight, functional groups, and linkage contents of GAM lignin were analyzed. This research provides valuable insights for masson pine in producing fermentable monosaccharides and acquiring lignin with enhanced processing properties. [Display omitted] • Studied the H 2 SO 4 -catalyzed GVL pretreatment under lignin-first strategy. • Proved the synergistic effect of H 2 SO 4 catalyst and GVL extraction. • The yield of converting masson pine waste into fermentable glucose can reach 97.3%. • Lignin's migration and structure changes under H 2 SO 4 -catalyzed GVL pretreatment. [ABSTRACT FROM AUTHOR]

• Dicarboxylic acid based DESs pretreatments were assisted by microwave radiation. • Various kinds of delignification and decrystallization of moso bamboo was achieved. • Tartaric acid based MW-DES pretreatment showed highest enzymatic conversion yield. • Multi-scale cellulose fibrils separation was beneficial for cellulase hydrolysis. Deep eutectic solvents (DESs) have received considerable interests as pretreatment solvents for biorefinery. In the present work, five kinds of dicarboxylic acids based DESs were introduced to pretreatments on moso bamboo (MB) with microwave irradiation assistance. Factors influencing the enzymatic conversion of MB cellulose to glucose were determined. With the fast heating, pretreated samples all present significant delignification and hemicelluloses matrix removal, thus improving the enzymatic conversion yield from 15% of MB to ~60%. For the DESs, hydrogen donors with less carbon atoms (oxalic acid) and more hydroxyl groups (tartaric acid) displayed higher efficiency due to separation of aggregated cellulose microfibrils. The microwave assisted DESs (MW-DESs) pretreatments also contributed to cellulose crystal variations including decrystallization and more exposure of hydrophobic surfaces, which are beneficial for followed cellulase adsorption and hydrolysis. The exploration of fast MW-DESs pretreatments may expand the potentials of lignocellulose biomass on effective and applicable biorefinery. [ABSTRACT FROM AUTHOR]

The recalcitrance in grasses varies according to cell type and tissue. In this study, dilute acid pretreatment was performed on Miscanthus × giganteus internodes that include rind and pith regions which showing heterogeneous structural and chemical changes. Pretreatment on pith effectively hydrolyzed 73.33% hemicelluloses and separated cohesive cell walls from the compound middle lamella due to lignin migration. Lignin droplets with an average diameter of 49.5 ± 29.3 nm were concurrently coalesced on wall surface, that in turn exposed more microfibrils deep in walls to be enzymatically hydrolyzed reaching 82.55%. By contrast, the rind with a relatively intergrated cell structure was covered by larger lignin droplets (101.2 ± 44.1 nm) and filled with inaccessible microfibrils limiting enzymatic sacchrification (31.50%). Taken together, the cellulose digestibility of biomass was not majorly influenced by cellulose crystallinity, while it was strongly correlated with the positive effects of hemicelluloses degradation, lignin redistribution, cellulose exposure and loosening cell wall structure. [ABSTRACT FROM AUTHOR]

[Display omitted] • A combined strategy for production of XOS and monosaccharides from poplar is proposed. • XOS with a low molecular weight is produced by acetic acid pretreatment. • Enzyme treatment on prehydrolyzate is favorable for producing XOS rich in X2-X3. • The applied acetic acid-mechanical method promotes the cellulase hydrolysis of poplar. Sequential biorefinery treatments of acetic acid (HAC) pretreatment, Papir Forsknings Institutet (PFI) milling and enzymatic hydrolysis were demonstrated for coproduction of xylooligosaccharides (XOS) and fermentable monosaccharides. Results indicated that 36.2% XOS (50.8% X2-X3) and 17.0% low DP xylans were achieved using a HAC pretreatment with a combined severity factor of 0.78. The HAC pretreatment resulted in a XOS-rich prehydrolyzate with a low molecular weight of 1.28 kDa. The endo -xylanase hydrolysis was conducted on the pretreatment liquor to elevate XOS yield and the content of higher-value X2-X3. Moreover, fermentable glucose production from the pretreated residue increased by 2.3 folds when introducing an additional step of PFI refining prior to enzymatic digestion. Properties of substrate including cellulose accessibility, crystallite size, crystalline index and water retention value were in close relationships with enzymatic digestibility. The implementation of proposed biorefinery process will give more insights into the efficient construction of a wood-derived sugar platform. [ABSTRACT FROM AUTHOR]

• Co-production of XOS and glucose was achieved by hot water pretreatment of birch. • Tween 80 obviously improved the enzymatic hydrolysis of birch. • The increase of accessibility and crystal size promoted enzymatic hydrolysis. • 1000 g of birch produced 104.6 g of XOS and 372.9 g of glucose. A green method for co-production of value-added xylooligosaccharides (XOS) and glucose from birch was demonstrated using hot water pretreatment. Effects of pretreatment severity factor (Log R 0) on XOS production and enzymatic hydrolysis were investigated. At Log R 0 of 4.05 (180 °C, 50 min), the maximum hydrolysis yield (80.8%) was obtained. At Log R 0 of 3.91 (170 °C, 70 min), the maximum XOS yield (46.1%) was obtained, however the hydrolysis yield decreased to 70.3%. To achieve both the high XOS yield and high glucose output, Tween 80 addition (0.075 g/g cellulose) was employed, leading to an improvement in hydrolysis yield from 70.3% to 89.4%. From a mass balance perspective, 104.6 g of XOS and 372.9 g of glucose could be produced from 1000 g birch. These results demonstrated that birch sawdust is a promising lignocellulosic material for co-production of XOS and glucose. [ABSTRACT FROM AUTHOR]

Discovering low-cost and green pretreatments for efficient deconstruction of lignocellulosic biomass recalcitrance is receiving growing interests. Herein, a novel electrogenerated alkaline hydrogen peroxide (EAHP) pretreatment was first proposed to produce H 2 O 2 and pretreat biomass concurrently in one pot. Results showed that the home-made electrode possess superior selectivity and stability. Under the optimal condition (30 mA·cm−2, 70 °C, 4 h), the novel pretreatment removed 76.3% of lignin while preserving cellulose, and the specific surface area and porosity of pretreated WS were greatly increased. The chemical and structural changes stimulated the enzymatic hydrolysis of cellulose and xylan reaching a maximum value of 83.7% and 90.8% respectively, which were significantly enhanced 4.1- and 5.3-fold compared to the original biomass. Overall, this work proposed a feasible biorefinery strategy for effective fractionation and utilization of lignocellulosic biomass. [Display omitted] • One-step proposed pretreatment combined electrocatalysis with biomass degradation. • H 2 O 2 was produced in situ solving transportation and storage problems. • High delignification was reached with low H 2 O 2 and NaOH demand. [ABSTRACT FROM AUTHOR]

• Pretreatment with Fe3+ or Al3+ increased enzymatic hydrolysis efficiency of WWS. • Fe3+ or Al3+ depolymerized lignin and decreased its adsorption capacity. • The adjusted lignin's chemical structures enhanced WWS's enzymatic hydrolysis. The addition of various metallic chlorides in pretreatment of lignocellulose have been widely reported to improve cellulose conversion via cellulolytic processing. However, the interaction mechanism between lignin and metallic cations is not well known. In this work, pretreatment with different concentrations of FeCl 3 and AlCl 3 were performed upon waste wheat straw to enhance enzymatic hydrolysis efficiency. Results showed that pretreatment with FeCl 3 and AlCl 3 could facilitate the enzymatic hydrolysis efficiency increasing from 50.4% to 82.9% and 76.6%, which was attributed to the enhancement of xylan removal by 33.8% (FeCl 3) and 36.5% (AlCl 3), respectively. Meanwhile, the surface charge, hydrophobicity, and protein adsorption capacity of lignin from waste wheat straw can be decreased by 3.3 mV, 0.6 L/g, 7.6 mg/g (FeCl 3). This was due to the depolymerization of lignin in metallic chlorides pretreatment. These findings will be used to further evaluate the effect of metallic chlorides in biorefinery pretreatment. [ABSTRACT FROM AUTHOR]

• Hydrothermal treatment showed high selectivity on removing xylan from poplar sawdust. • A combined process of hydrothermal and enzymatic hydrolysis was established. • Xylooligosaccharides with high proportion of xylobiose and xylotriose were produced. • The structure of low DP xylans relys on pretreatment severity factors. A promising approach for production of value-added xylooligosaccharides (XOS) from poplar was developed by combining hydrothermal pretreatment and endo -xylanase post-hydrolysis. Results showed that the 35.4% XOS (DP 2–6) and 17.6% low DP xylans (DP > 6) were obtained at the identified optimal condition (170 °C, 50 min) for hydrothermal pretreatment. Structural features of low DP xylans generated during the hydrothermal pretreatment were examined, revealing that low DP xylans are mainly comprised of 4-O-methylglucuronic xylan and are involved in lignin carbohydrate complexes. Moreover, higher pretreatment intensity promoted the cleavage of side-chain substituents including arabinose and glucuronic acid groups. The subsequent endo -xylanase hydrolysis of the pretreatment liquor hydrolyzed low DP xylans, contributing to a significant improvement in xylobiose and xylotriose proportions. This combined strategy resulted in a XOS with conversion yield of 44.6% containing 78.7% xylobiose and xylotriose starting from the initial xylan in raw poplar. [ABSTRACT FROM AUTHOR]

• A combined pretreatment was established based on hydrothermal and DES treatment. • Hydrothermal pretreatment produced 53.2% xylo -oligosaccharides from poplar sawdust. • Surface lignin content impeded enzymatic hydrolysis of combined pretreated poplar. • Bovine serum albumin prevented surface lignin from non-productively binding enzymes. Full utilization of lignocellulose is critical for its biorefinery development. In this study, a sustainable biorefinery process based upon poplar sawdust was established using sequential hydrothermal and deep eutectic solvent treatment (HP-DES). Results showed that single hydrothermal pretreatment (HP) could produce 53.2% xylo -oligosaccharides (XOS) (based on raw xylan), while the enzymatic digestibility was low. Conversely, single DES treatment achieved effective enzymatic digestibility but low XOS yields. As compared to HP, both DES treatment and HP-DES showed high selectivity for lignin removal and high glucose yield. Surprisingly, most of HP-DES residues had obviously lower enzymatic digestibilities than those of single DES residues. This was mainly explained by the differences of the surface lignin contents between DES and HP-DES residues. Moreover, nearly complete enzymatic hydrolysis of HP-DES residues was achieved with the addition of bovine serum albumin. This work demonstrated this HP-DES yielded XOS, fermentable sugar, and pure lignin with high processibility. [ABSTRACT FROM AUTHOR]

• A novel clean pretreatment method was established by humic acid-aided dilute acid pretreatment. • The mixed pretreatment improved the enzymatic hydrolysis efficiency of WWS. • Humic acid helped removal of lignin in pretreatment process. Traditional surfactants have been reported to enhance enzymatic saccharification of lignocellulose, however, it is important to transfer these findings to a system that uses a high-efficiency and low-toxicity natural surfactant instead. In this work, a novel hybrid method involving use of the natural surfactant (humic acid, HA) during mild acid (H 2 SO 4) pretreatment was developed for waste wheat straw (WWS) biorefinery. The HA was found to help remove lignin up to 40.6%, and hemicellulose up to 96.2%. As a result of these changes, the enzymatic hydrolysis efficiency reached as high as 92.9%. The success of enzymatic digestion was partly attributed to the improved accessibility of cellulose to cellulase and changes in lignocellulose structures. We anticipate that these findings will be used to further evaluate HA as a beneficial surfactant in biorefinery pretreatment processes, and perhaps spur others to identify other natural surfactants that may prove even more effective. [ABSTRACT FROM AUTHOR]