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Deep eutectic solvents (DES) pretreatment is a promising approach to decrease “biomass recalcitrance” and boost the cellulose bioconversion as well as lignin valorization. In this study, a short-time DES pretreatment strategy was performed to enhance the production of high-yield fermentable sugars and tailored lignin nanoparticles (LNPs) from abaca. The glucose yield reached 92.4% under the optimal pretreatment condition (110 °C, 30 min), which was dramatically increased in comparison with that (9.5%) of control abaca. Simultaneously, nuclear magnetic resonance (NMR) and gel permeation chromatography (GPC) techniques indicated that the removed and regenerated DES lignin fractions displayed depolymerized structures and have relatively low molecular weight with relatively homogeneous morphology and narrow size distribution. Transmission electron microscope (TEM) analysis indicated that these lignin fractions are LNPs and the size of the optimal LNPs fraction is ranged from 30 nm to 50 nm. Moreover, all the DES lignin exhibited excellent antioxidant activities as compared to the commercial antioxidant butylated hydroxytoluene (BHT), which can be used as a promising natural antioxidant in industry. In short, this study demonstrated that the short-time DES pretreatment will improve the enzymatic digestibility and facilitate the controllable production and valorization of LNPs from abaca biomass, which will further promote the economic and overall benefits of biorefinery.

Elucidating the chemical and structural characteristics of hemicelluloses and lignin in the p-coumarate 3-hydroxylase (C3H) down-regulated poplar wood will be beneficial to the upstream gene validation and downstream biomass conversion of this kind of transgenic poplar. Herein, the representative hemicelluloses and lignin with unaltered structures were prepared from control (CK) and C3H down-regulated 84K poplars. Modern analytical techniques, such as 13C NMR, 2D-HSQC NMR, and gel chromatography (GPC), were performed to better delineate the structural changes of hemicelluloses and lignin caused by transgenesis. Results showed that both the hemicelluloses (H-CK and H-C3H) extracted from control and C3H down-regulated poplar wood have a chain backbone of (1→4)-β-D-Xylan with 4-O-Me-α-D-GlcpA as side chain, and the branch degree of the H-C3H is higher than that of H-CK. With regarding to the lignin macromolecules, NMR results demonstrated that the syringyl/guaiacyl (S/G) ratio and dominant substructure β-O-4 linkages in C3H down-regulated poplar were lower than those of control poplar wood. By contrast, native lignin from C3H down-regulated poplar wood exhibited higher contents of p-hydroxybenzoate (PB) and p-hydroxyphenyl (H) units. In short, C3H down-regulation resulted in the chemical and structural changes of the hemicelluloses and lignin in these poplar wood. The identified structures will facilitate the downstream utilization and applications of lignocellulosic materials in the biorefinery strategy. Furthermore, this study could provide some illuminating results for genetic breeding on the improvement of wood properties and efficient utilization of poplar wood.

Elucidating the chemical and structural characteristics of hemicelluloses and lignin in the p-coumarate 3-hydroxylase (C3H) down-regulated poplar wood will be beneficial to the upstream gene validation and downstream biomass conversion of this kind of transgenic poplar. Herein, the representative hemicelluloses and lignin with unaltered structures were prepared from control (CK) and C3H down-regulated 84K poplars. Modern analytical techniques, such as 13C NMR, 2D-HSQC NMR, and gel chromatography (GPC), were performed to better delineate the structural changes of hemicelluloses and lignin caused by transgenesis. Results showed that both the hemicelluloses (H-CK and H-C3H) extracted from control and C3H down-regulated poplar wood have a chain backbone of (1→4)-β-D-Xylan with 4-O-Me-α-D-GlcpA as side chain, and the branch degree of the H-C3H is higher than that of H-CK. With regarding to the lignin macromolecules, NMR results demonstrated that the syringyl/guaiacyl (S/G) ratio and dominant substructure β-O-4 linkages in C3H down-regulated poplar were lower than those of control poplar wood. By contrast, native lignin from C3H down-regulated poplar wood exhibited higher contents of p-hydroxybenzoate (PB) and p-hydroxyphenyl (H) units. In short, C3H down-regulation resulted in the chemical and structural changes of the hemicelluloses and lignin in these poplar wood. The identified structures will facilitate the downstream utilization and applications of lignocellulosic materials in the biorefinery strategy. Furthermore, this study could provide some illuminating results for genetic breeding on the improvement of wood properties and efficient utilization of poplar wood.

A synergistic pretreatment that realizing effective fractionation and targeted valorization can guarantee the implementability to future biorefinery scenario. In the present study, a stepwise approach using hydrothermal and deep eutectic solvents (DES) pretreatment was developed to preferentially dissociate hemicelluloses and further remove lignin from poplar, while retaining a cellulose-rich substrate that can be easily digested via enzymatic saccharification to obtain glucose. Results showed that the hydrothermal filtrate is mainly composed of xylooligosaccharide (XOS), monosaccharides, byproducts, and xylan-type hemicelluloses, which have homogenous structures and uniform molecular weights distribution as well as excellent antioxidant activity. Subsequent DES pretreatment further removed the lignin barriers, leading to a remarkable increase in the saccharification efficiency from 15.72% to 96.33% under optimum conditions for enzymatic hydrolysis. In short, the integrated pretreatment is effective for dissociating and chemical conversion of poplar wood, which was reasonable to promote the frontier of highly available biorefinery.

Lignin is the most abundant aromatic biomacromolecule on the earth, which is an attractive raw material for producing bio-based chemicals, materials, and fuels. However, the complexity, heterogeneity, and variability of the lignin structure always hinders the value-added application of different sources of raw materials. In this study, double enzymatic lignin (DEL) was isolated from balsa grown for different lengths of time to understand the structural variations of lignin macromolecules during the growth of balsa for the first time. Confocal Raman microscopy and component analysis were used to monitor the lignin accumulation in balsa. Meanwhile, the structural characteristics and chemical reactivity of DELs were synthetically characterized by advanced 2D-HSQC and 31P-NMR techniques. It was found that the balsa lignin is a typical hardwood lignin and it is overwhelmingly composed of C–O bonds (i.e., β-O-4 linkages), whose content is elevated with increasing tree-age. Interestingly, carbon–carbon linkages (e.g., β-β and β-5) in these DELs isolated from 3-and 5-year-old balsa are gradually disappearing. Considering the increasing molecular weight of DELs with tree-age, it was concluded that lignin macromolecules in balsa wood were gradually polymerized within the growth period. Furthermore, abundant C–O linkages with less C–C linkages in the DELs from 3 and 5-year-old balsa wood suggested that these feedstocks are promising in current lignin-first biorefinery and will facilitate the conversion of aromatic chemicals from the lignin macromolecule. In short, a comprehensive understanding of native lignin during the growth of balsa wood will not only advance the understanding of biosynthetic pathways of lignin biopolymer, but also facilitate the deconstruction and value-added applications of this kind of feedstock.

Reducing the “biomass recalcitrance” and simultaneously improving the efficiency of deconstruction and conversion is vitally important in a biorefinery process. Herein, a microwave-assisted deep eutectic solvents (DES) pretreatment was developed to deconstruct the control and transgenic (C3H, HCT and C3H + HCT co-inhibition) poplars, and improve the lignin extractability and valorization. NMR and GPC results showed that native lignin (Double Enzymatic Lignin, DEL) in different poplars exhibited slightly different structural characteristics, affecting the subsequent lignin extractability and value-added applications. After two kinds of DES (ethylene glycol-based and glycerol-based DES) pretreatments, the yield of DES lignin was obviously increased to 45.38–53.09 % and 46.38–54.30 % in transgenic poplar woods as compared to control poplar wood (37.25 and 38.86 %). In addition, molecular weight, and abundances of different linkages (β-O-4, β-β, β-5, etc.) in the DES lignin fractions were significantly decreased, suggesting the microwave-assisted DES pretreatment has a strong deconstruction ability towards to poplar wood. Moreover, the rapid and efficient pretreatment facilitated the isolation of the lignin fractions from transgenic poplars, and the regenerated DES lignin fractions exhibited excellent antioxidant properties, which will lay the foundation for the lignin valorization. Furthermore, the enzymatic saccharification ratios of the DES pretreated substrates were significantly increased to 87.36–96.55 % in control and transgenic poplar woods, indicating that microwave-assisted DES pretreatment indeed boosted cellulose bioconversion. In short, the combination of genetic modification and DES pretreatment can significantly reduce the “biomass recalcitrance” and promote the biomass valorization.

In this study, lignin with fine structures and facile enzymatic saccharifying residue were successively dissociated based on the lignin-first biomass deconstruction strategy. In the lignin-first process, aldehyde-protected lignin fractions were firstly isolated by acid-catalyzed dioxane extraction in the presence of formaldehyde (FA) and acetaldehyde (AA) and then analyzed by advanced nuclear magnetic resonance (NMR) spectroscopy and gel permeation chromatography (GPC). The optimized hydrogenolysis of the extracted lignin (LFA and LAA) resulted in a high yield (42.57% and 33.00%) of lignin monomers with high product selectivity (mainly 2,6-dimethoxy-4-propylphenol) (39.93% and 46.61%). Moreover, the cellulose-rich residues were saccharified into fermentable glucose for bioethanol production. The glucose yield of the substrate (RAA) reached to 75.12%, which was significantly higher than that (15.4%) of the substrate (RFA). In short, the lignin-first biomass deconstruction by adding AA is a promising and sustainable process for producing value-added products (energy and fine chemicals) from lignocellulosic biomass.