A novel cetyltrimethylammonium bromide-based deep eutectic solvent pretreatment of rice husk to efficiently enhance its enzymatic hydrolysis

Exploration of biomass fractionation and lignin removal for enhancing enzymatic digestion of wheat-stalk through deep eutectic solvent Cetyl trimethyl ammonium chloride:Lactic acid treatment

The cationic surfactant-based deep eutectic solvents (DESs) have attracted extensive attention due to their effectual destruction of the natural anti-degradation barrier structure in lignocellulose. In this research, functional DES Cetyl trimethyl ammonium chloride:Lactic acid (CTAC:LA molar ratio 1:0.5 to 1:6) was fabricated for pretreating wheat-stalk. The relationships of accessibility, lignin removal, xylan separation, and enzymolysis efficiency were explored. The highest delignification (88.3 %) and xylan removal (89.0 %) were obtained through the treatment with CTAC:LA (1:4, mol/mol, 160 °C, 60 min), acquiring 86.8 % of enzymolysis efficiency. The structure of CTAC:LA-treated wheat-stalk was changed to porous state, while the accessibility and crystallinity were substantially improved to 668.2 mg/g and 57.6 %, respectively. The lignin surface area declined from 672.7 to 335.4 m2/g. Furthermore, the structure of lignin disrupted by CTAC:LA was analyzed by 2D-HSQC NMR, implying that CTAC:LA could cleave the CO covalent bond and CC bond and degrade the S- and H-units in wheat-stalk lignin through interaction. The potential pretreatment mechanism was proposed through comprehensive exploration at the molecular level and macro level, and this built pretreatment process held great promise for valorizing biomass into highly valuable chemicals.

Valorization of rapeseed straw through the enhancement of cellulose accessibility, lignin removal and xylan elimination using an n-alkyltrimethylammonium bromide-based deep eutectic solvent

n-Alkyltrimethylammonium bromide (CnTAB)-based deep eutectic solvent (DESs) has potential in the efficient delignification and utilization of carbohydrates in biomass. In this research, DESs containing Brønsted acid and Lewis acid were prepared with CnTAB (alkyl-chain length 12-18), organic acids and metal chlorides, and the optimal treatment conditions were acquired by pretreatment optimization. Through the pretreatment with TTAB/LCA/Fe3+ (1:4:0.0111, mol:mol:mol) (162.5 °C, 61.7 min), lignin (89.2 %) and xylan (77.9 %) were effectively eliminated, and the hydrophobicity of rapeseed straw substantially declined from 4.62 to 2.09 m2/g, acquiring the highest enzymatic saccharification efficiency of 92.5 %. The relationship of DES properties and enzymatic saccharification efficiency was explored. Additionally, hemicellulose in rapeseed straws could be efficiently transformed into furfural (3.75 g/L) and xylo-oligosaccharides (3.64 g/L). To clarify the structural and property changes brought by pretreatment, rapeseed straws were testified by FT-IR, SEM and CLSM and deeply discussed. The interaction between lignocellulose and TTAB/LCA/Fe3+ was elucidated by molecular dynamics simulations and quantum chemical calculations, explaining the effectual treatment performance and hemicellulose upgrading at the molecular level. Eventually, a potential pretreatment mechanism of TTAB/LCA/Fe3+ was proposed. This established TTAB/LCA/Fe3+ treatment holds great promise for valorization of biomass into biofuels and biobased chemicals.

Implementing efficient and sustainable pretreatment of Sorghum stalks for delignification and xylan separation with a ternary deep eutectic solvent under mild conditions

Acidic deep eutectic solvent (DES) has garnered significant attention in biomass pretreatment due to its effectiveness. Octadecyl trimethyl ammonium chloride (OTAC) is a highly efficient surfactant, which is expected to create new DES with additional pretreatment functions. Accordingly, a new ternary deep eutectic solvent (TDES) was synthesized from OTAC, propionic acid (PA), and p-toluene sulfonic acid (p-TsOH) for pretreating sorghum stalk under the relatively mild condition to enhance enzymatic saccharification of sorghum stalks. Through the treatment with OTAC:PA:p-TsOH (1:2:0.1, mol:mol:mol) at 80 °C for 30 min, the enzymolysis efficiency of sorghum stalks was increased to 69.3 %. The accessibility of sorghum stalk to cellulose was increased to 414.3 mg dye/g cellulose while the surface area of lignin decreased to 517 m2/g. Along with the altered cellulose crystal structure and surface properties, the pretreatment mechanism for improving enzymatic hydrolysis capacity was proposed. Overall, this research implemented an efficient pretreatment using TDES OTAC:PA:p-TsOH for the valorization of sorghum stalk, providing a novel approach for the depolymerization and value-added utilization of lignocellulosic biomass in biorefining technology.

Optimisation of the Ethanol Fermentation Process Using Hydrothermal Pretreatment of Cellulose Waste-Effect of Fermentation Pattern and Strain

Suitable fermentation substrates and fermentation modes can effectively improve the fermentation ethanol yield. In this study, we optimised the hydrothermal pretreatment conditions by orthogonal optimisation using waste tissue paper as substrate. These conditions consisted of 50 min duration in a high-pressure reactor with pure water as solvent at a temperature of 160 °C. The biomass to water ratio was maintained at a constant level. The cellulose content of the pretreated TP was 81.19 ± 4.06%, which was an increase of 21.59% compared to the blank control. The 72 h reducing sugar yield of pretreated TP was 0.61 g sugar/g paper, which was 38.64% higher than that of untreated TP. Subsequently, the pretreated TP was fermented under optimal conditions. The mixed group of Saccharomyces cerevisiae and Candida shehatae (SC) showed a distributed saccharification fermentation pattern, with an ethanol yield of 28.11 g/L in 72 h. On the other hand, the single Saccharomyces cerevisiae (S) exhibited a homobloc saccharification fermentation pattern, with an ethanol yield of 35.15 g/L in 72 h.

Promoted lignocellulose fractionation and improved enzymatic hydrolysis of corn stalks through cationic surfactant combined with deep eutectic solvent pretreatment

The efficient conversion of lignocellulose relies on the implementation of an effective pretreatment strategy. Cationic surfactants combined with deep eutectic solvent ([Betaine][LA] was employed as a novel pretreatment strategy for treating corn stalks. Valuable insights were provided on the impact of the surfactant hydrophobic segment length on pretreatment efficacy. The specific pretreatment conditions were optimized by single factor and orthogonal experiment. Octadecyl trimethyl ammonium bromide (OTAB, 1.5 wt%) with the longest hydrophobic part combined with [Betaine][LA] (Betaine-to-LA molar ratio 1:4) achieved the best pretreatment effect (delignification 92.8 %, xylan elimination 91.1 %) when severity factor reached 4.26, meanwhile, 1.7 g/L xylo-oligosaccharides and 4.4 g/L furfural were detected in pretreatment liquid due to the hydrolysis of hemicellulose in corn stalks with acidic deep eutectic solvent [Betaine][LA]. The relative saccharification activity reached 2.7 times of raw material, while the lignin surface area significantly decreased, leading to enhanced cellulose accessibility. Additionally, molecular perspective provided by molecular dynamics showed the elimination of lignin and xylan was facilitated by strong interaction of hydrogen-bond and van der Waals force between lignin and hemicellulose with [Betaine][LA] + OTAB. Overall, the effectiveness and potential of cationic surfactant combined deep eutectic solvent pretreatment strategy for lignocellulose pretreatment was revealed.

Influence of biphasic phenoxyethanol-alkaline pretreatment on the correlation between inter-structure and enzymatic hydrolysis in bamboo residues

The effective promotion of delignification (67.6 %) and xylan removal (44.8 %) from bamboo residues using a 2-phenoxyethanol/sodium hydroxide solution (P/A) system is demonstrated, while simultaneously enriching oligosaccharides contents of the pre-hydrolysate to 10.2 g/L. Increasing the P/A ratio from 0:1 to 4:1 improves the enzymatic digestibility of the substrates from 55.7 % to 70.1 % at 100 °C and from 73.8 % to 83.7 % at 120 °C. Furthermore, partial correlation analysis demonstrates that the physiochemical properties, including delignification, xylan removal, and crystallinity, show a significant positive correlation with enzymatic hydrolysis efficiency. Higher temperatures and P/A ratios during alkaline biphasic pretreatment promote the shrinkage of plant cells and delignification, with temperature being a particularly significant driver. These findings provide valuable insights into the alkaline and biphasic pretreatment of biomass and facilitate the optimization of the bio-refining system.

Efficient extraction of lignin from moso bamboo by microwave-assisted ternary deep eutectic solvent pretreatment for enhanced enzymatic hydrolysis

Applications of deep eutectic solvent (DES) systems to separate lignocellulosic components are of interest to develop environmentally friendly processes and achieve efficient utilization of biomass. To enhance the performance of a binary neutral DES (glycerol:guanidine hydrochloride), various Lewis acids (e.g., AlCl3·6H2O, FeCl3·6H2O, etc.) were introduced to synthesize a series of ternary DES systems; these were coupled with microwave heating and applied to moso bamboo. Among the ternary DES systems evaluated, the FeCl3-based DES effectively removed lignin (81.17%) and xylan (85.42%), significantly improving enzymatic digestibility of the residual glucan and xylan (90.15% and 99.51%, respectively). Furthermore, 50.74% of the lignin, with high purity and a well-preserved structure, was recovered. A recyclability experiment showed that the pretreatment performance of the FeCl3-based DES was still basically maintained after five cycles. Overall, the microwave-assisted ternary DES pretreatment approach proposed in this study appears to be a promising option for sustainable biorefinery operations.

Improving saccharification efficiency of corn stover through ferric chloride-deep eutectic solvent pretreatment

An effective deep eutectic solvent (DES) and Iron(III) chloride (FeCl3) combination pretreatment system was developed to improve the removal efficiency of lignin and hemicellulose from corn stover (CS) and enhance its saccharification. N-(2-hydroxyethyl)ethylenediamine (NE) was selected as the hydrogen-bond-donor for preparing ChCl-based DES (ChCl:NE), and a mixture of ChCl:NE (60 wt%) and FeCl3 (0.5 wt%) was utilized for combination pretreatment of CS at 110 ℃ for 50 min. FeCl3/ChCl:NE effectively removed lignin (87.0 %) and xylan (55.9 %) and the enzymatic hydrolysis activity of FeCl3/ChCl:NE-treated CS was 5.5 times that of CS. The reducing sugar yield of pretreated CS was 98.6 %. FeCl3/ChCl:NE significantly disrupted the crystal structure of cellulose in CS and improved the removal of lignin and hemicellulose, enhancing the conversion of cellulose and hemicellulose into monomeric sugars. Overall, this combination of FeCl3 and DES pretreatment methods has high application potential for the biological refining of lignocellulose.

Synergistic microwave and acidic deep eutectic solvent-based pretreatment of Theobroma cacao pod husk biomass for xylooligosaccharides production

The bioconversion of lignocellulosic biomass into novel bioproducts is crucial for sustainable biorefineries, providing an integrated solution for circular economy objectives. The current study investigated a novel microwave-assisted acidic deep eutectic solvent (DES) pretreatment of waste cocoa pod husk (CPH) biomass to extract xylooligosaccharides (XOS). The sequential DES (choline chloride/citric acid, molar ratio 1:1) and microwave (450W) pretreatment of CPH biomass was effective in 67.3% xylan removal with a 52% XOS yield from total xylan. Among different XOS of varying degrees of polymerization, a higher xylobiose content corresponding to 69.3% of the total XOS (68.22 mg/g CPH) from liquid fraction was observed. Enzymatic hydrolysis of residual xylan from pretreated CPH biomass with low commercial xylanase (10 IU/g) concentration yielded 24.2% XOS. The MW-ChCl/citric acid synergistic pretreatment approach holds great promise for developing a cost-effective and environmentally friendly method contributing to the sustainable production of XOS from agricultural waste streams.

Combination of solid acid and solvent pretreatment for co-production of furfural, xylooligosaccharide and reducing sugars from Phyllostachys edulis

The efficient utilization of biomass resources has gained widespread attention in current research. This study focused on the conversion of hemicellulose into xylo-oligosaccharides and furfural, as well as enhanced cellulose saccharification and lignin removal from residual biomass. The solid acid catalyst AT-Sn-MMT was prepared by sulfonation and tin ion loading of montmorillonite K-10. In a mixture of deep eutectic solvent and γ-valerolactone (3:7, v/v), AT-Sn-MMT was used to catalyze Phyllostachys edulis (PE) at 160 °C for 20 min, obtaining a furfural yield of 85.7 % and 1.5 g/L xylo-oligosaccharides. The delignification of pretreated PE was 59.5 %, reaching an accessibility of 221.3 g dye/g material. While the enzymatic saccharification efficiency was increased to 73.1 %. This work drew on the merits of solid acid catalysts and mixed solvent systems, and this constructed pretreatment method could be efficiently applied for co-production of reducing sugars, xylooligosaccharide and furfural, realizing the efficient valorization of PE.

Optimizing bioconversion processes of rice husk into value-added products: D-psicose, bioethanol, and lactic acid

Rice husk, rich carbon content, is an agricultural waste produced globally at an amount of 120 million tons annually, and it has high potential as a biorefinery feedstock. Herein, we investigated the feasibility of producing various products as D-psicose, bioethanol and lactic acid from rice husk (RH) through a biorefinery process. Alkali-hydrogen peroxide-acetic acid pretreatment of RH effectively removed lignin and silica, resulting in enzymatic hydrolysis yield of approximately 86.3% under optimal hydrolysis conditions. By using xylose isomerase as well as D-psicose-3-epimerase with borate, glucose present in the RH hydrolysate was converted into D-psicose with a 40.6% conversion yield in the presence of borate. Furthermore, bioethanol (85.4%) and lactic acid (92.5%) were successfully produced from the RH hydrolysate. This study confirmed the high potential of RH as a biorefinery feedstock, and it is expected that various platform chemicals and value-added products can be produced using RH.

Quantification of alkalinity of deep eutectic solvents based on (H-) and NMR

Alkaline deep eutectic solvents (DESs) have been widely employed across diverse fields. A comprehensive understanding of the alkalinity data is imperative for the comprehension of their performance. However, the current range of techniques for quantifying alkalinity is constrained. In this investigation, we formulated a series of alkaline DESs and assessed their basicity properties through a comprehensive methodology of Hammett functions alongside 1H NMR analysis. A correlation was established between the composition, structure and alkalinity of solvents. Furthermore, a strong linear correlation was observed between the Hammett basicity (H-) of solvents and initial CO2 adsorption rate. Machine learning techniques were employed to predict the significant impact of alkaline functional components on alkalinity levels and CO2 capture capacity. This study offers valuable insights into the design, synthesis and structure-function relationship of alkaline DESs.

Combined sulfuric acid and choline chloride/glycerol pretreatment for efficiently enhancing enzymatic saccharification of reed stalk

In this study, an efficient combination of pretreatment solvents involving Choline chloride/Glycerol (ChCl/Gly) and H2SO4 was firstly developed to assess the pretreatment performance and determine optimal pretreatment conditions. The results illustrated that the H2SO4-[ChCl/Gly] combination efficiently removed lignin (52.6%) and xylan (80.5%) from the pretreated reed stalk, and subsequent enzymatic hydrolysis yielded 91.1% of glucose. Furthermore, several characterizations were conducted to examine the structural and morphological changes of the reed stalk, revealing apparently enhanced accessibility (128.4 to 522.6 mg/g), reduced lignin surface area (357.9 to 229.5 m2/g), and substantial changes on biomass surface. Based on the aforementioned study, possible mechanisms for the H2SO4-[ChCl/Gly] pretreatment of reed stalks were proposed. The comprehensive understanding of combined H2SO4-[ChCl/Gly] pretreatment system for enhancing the saccharification of the reed stalk was interpreted in this work. Overall, this novel approach could be efficiently applied to pretreat and saccharify reed stalks, empowering the biomass refining industry.

Efficient co-production of reducing sugars and xylooligosaccharides via clean hydrothermal pretreatment of rape straw

Hydrothermal treatment was applied to pretreat rape straw for the efficient co-production of reducing sugars and xylooligosaccharides. It was observed that hydrothermal treatment using water as solvent and catalyst destructed the compact structure of rape straw and increased its enzymatic digestion efficiency from 24.6% to 92.0%. Xylooligosaccharide (3.3 g/L) was acquired after the treatment under 200 °C for 60 min (severity factor Log Ro = 4.7). With increasing pretreatment intensity from 3.1 to 5.4, the hemicellulose removal increased from 14.4% to 100%, and the delignification was raised from 12% to 44%. Various characterization proved that the surface morphology of treated material showed a porous shape, while the cellulose accessibility, lignin surface area and lignin hydrophobicity were greatly improved. Consequently, hydrothermal pretreatment played a vital role in the sustainable transformation of biomass to valuable biobased compounds, and had a wide range of application prospects in lignocellulosic biorefining.

Employing deep eutectic solvent synthesized by cetyltrimethylammonium bromide and ethylene glycol to advance enzymatic hydrolysis efficiency of rape straw

An efficient deep eutectic solvent (DES) was synthesized by cetyltrimethylammonium bromide (CTAB) and ethylene glycol (EG) and employed to treat rape straw (RS) for advancing enzymatic saccharification in this work. By optimizing the pretreatment parameters, the results displayed that the novel DES was strongly selective towards removing lignin and xylan while preserving cellulose. Under optimum conditions with 1:6 of CTAB: EG in DES, 180 °C and 80 min, the enzymatic hydrolysis efficiency of RS was enhanced by 46.0% due to the 62.2% of delignification and 53.2% of xylan removal during CTAB: EG pretreatment. In terms of the recalcitrant structure of RS, DES pretreatment caused the increment of cellulosic accessibility, reduction of hydrophobicity and surface area of lignin, and migration of cellulosic crystalline structure, which was associated with its enzymatic hydrolysis efficiency. Overall, this study presented an emerging method for the effective fractionation and valorization of lignocellulosic biomass within biorefinery technology.

Novel supramolecular deep eutectic solvent-enabled in-situ lignin protection for full valorization of all components of wheat straw

Lignin is usually deemed as an inhibitor to enzymatic hydrolysis of cellulose due to its physical barrier, non-productive adsorption, and steric hindrance. Herein, a novel supramolecular deep eutectic solvent (SUPRADES), comprising ethylene glycol and citric acid in 5:1 M ratio, and β-cyclodextrin (β-CD) in a concentration of 3.5% (w/w), was developed to be efficient for pretreating wheat straw. The delignification rate, cellulose enzymatic digestibility, and hemicellulose removal reached 90.45%, 97.36% and 87.24%, respectively, which may be attributed to the introduction of β-CD with superior ability of both adsorption and in-situ lignin protection to efficiently remove lignin with intact structure from cellulose surface. The mechanisms of high-efficiency lignin extraction/protection were systematically illustrated by adsorption kinetics. Moreover, Trichosporon cutaneum grown on the hemicellulose and cellulose fractions after pretreatment afforded 8.8 g total lipids from 100 g wheat straw. The green SUPARDES pretreatment strategy offers a new avenue for upgrading lignocellulose to biofuels.

Efficient co-production of xylooligosaccharides, furfural and reducing sugars from yellow bamboo via the pretreatment with biochar-based catalyst

The research on the efficient use of biomass to produce chemical products has received extensive attention. In this work, a novel heterogeneous biocarbon-based heterogeneous catalyst AT-Sn-YB was prepared using yellow bamboo (YB) as a carrier, and its physical properties were proved to be good by various characterization and stability experiments. In the γ-valerolactone/water (3:1, v/v) medium containing 100 mM CuCl2, the use of AT-Sn-YB (3.6 wt%) under 170 °C for 20 min was applied to catalyze YB into furfural (80.3% yield), accompanied with 2.8 g/L xylooligosaccharides. The YB solid residue obtained from treatment was efficiently saccharified to reducing sugars (17.2 g/L). Accordingly, comprehensive understanding of efficiently co-producing xylooligosaccharides, furfural and reducing sugars from YB was demonstrated via the pretreatment with biochar-based catalyst. This study innovatively used a new type of solid acid to complete the efficient co-production of chemical products, and realized the value-added utilization of yellow bamboo.

Improved enzymatic saccharification of bulrush via an efficient combination pretreatment

Glycerol (Gly) was selected as hydrogen-bond-donor for preparing ChCl-based DES (ChCl:Gly), and the mixture of ChCl:Gly (20 wt%) and NaOH (4 wt%) was utilized for combination pretreatment of bulrush at 100 °C for 60 min (severity factor LogRo = 1.78). The effects of DES pretreatment on the chemical composition, microstructure, crystal structure, and cellulase hydrolysis were explored. NaOH-ChCl:Gly could remove lignin (80.1%) and xylan (66.8%), and the enzymatic digestibility of cellulose reached 87.9%. The accessibility of bulrush was apparently increased to 645.2 mg/g after NaOH-ChCl:Gly pretreatment. The hydrophobicity and lignin surface area were reduced to 1.56 L/g and 417 m2/g, respectively. The crystallinity of cellulose was increased from 20.8% to 55.6%, and great changes in surface morphology were observed, which explained the improvement of enzymatic hydrolysis efficiency. Overall, DES combined with alkali treatment could effectively promote the removal of lignin and xylan in bulrush, thus the relative saccharification activity was greatly affected.

Comprehensive understanding of enzymatic saccharification of Betaine:Lactic acid-pretreated sugarcane bagasse

Green solvents, especially deep eutectic solvents (DESs), are widely applied to pretreat biomass for enhancing its enzymatic hydrolysis. In this work, lactic acid was selected as the hydrogen-bond-donor to prepare Betaine-base DES (Betaine:LA), The DES was utilized to pretreat sugarcane bagasse (SCB) at 160 ℃ for 80 min (severity factor LogR0 = 3.67). The influences of Betaine:LA treatment on the chemical composition, crystal and microstructure structure of cellulose, and cellulase digestion were investigated. The results showed that the lignin (47.1%) and xylan (44.6%) were removed, the cellulase digestibility of Betaine:LA-treated SCB was 4.2 times that of the raw material. This improved efficiency was attributed to the enhanced accessibility of cellulose, the weakened surface area of lignin, the declined hydrophobicity, and the decreased crystallinity of cellulose. Several compelling linear correlations were fitted between enzymatic hydrolysis and these alterations of physicochemical features, comprehensively understanding enzymatic saccharification of Betaine:LA-pretreated SCB.

Comparative Study of Adsorption of Methylene Blue and Basic Red 9 Using Rice Husks of Different Origins

Methylene blue (MB) and basic red 9 (BR9) are cationic dyes that are commonly used in the dye industry and negatively affect humans and other living organisms. This study compares the performance of Indonesian rice husk (IRH) and Hungarian rice husk (HRH) as bio-adsorbents for removing MB and BR9 from aqueous solutions. Chemical content, zeta potential, and Fourier-transform infrared spectroscopy analyses were used to characterize the rice husks (RHs). Adsorption studies were performed through batch experiments involving several parameters, namely, pH, adsorbent dose, initial dye concentration, contact time, and temperature to observe the self-association (aggregation) of MB and BR9. Adsorption kinetic studies showed that maximum dye removal was achieved at a contact time of 120 min. MB and BR9 adsorption followed a pseudo-second order kinetic model, and the BET multilayer isotherm model provided a better fit to the experimental data of MB and BR9 adsorption. The IRH adsorption capacities were 15.0 mg/g for MB and 7.2 mg/g for BR9, whereas those of HRH were 24.4 mg/g for MB and 8.3 mg/g for BR9. Therefore, these RHs are potential bio-adsorbents for removing MB and BR9 from aqueous solutions.

Improved biotransformation of lignin-valorized vanillin into vanillylamine in a sustainable bioreaction medium

Lignin is a critical biopolymer for creating a large number of highly valuable biobased compounds. Vanillin, one of lignin-derived aromatics, can be used to synthesize vanillylamine that is a key fine chemical and pharmaceutical intermediate. To produce vanillylamine, a productive whole-cell-catalyzed biotransformation of vanillin was developed in deep eutectic solvent - surfactant - H2O media. One newly created recombinant E. coli 30CA cells expressing ω-transaminase and L-alanine dehydrogenase was employed to transform 50 mM and 60 mM vanillin into vanillylamine in the yield of 82.2% and 8.5% under 40 °C, respectively. The biotransamination efficiency was enhanced by introducing surfactant PEG-2000 (40 mM) and deep eutectic solvent ChCl:LA (5.0 wt%, pH 8.0), and the highest vanillylamine yield reached 90.0% from 60 mM vanillin. Building an effective bioprocess was utilized for transamination of lignin-derived vanillin to vanillylamine with newly created bacteria in an eco-friendly medium, which had potential application for valorization of lignin to value-added compounds.

Cold plasma pretreatment reinforces the lignocellulose-derived aldehyde inhibitors tolerance and bioethanol fermentability for Zymomonas mobilis

BACKGROUND

Lignocellulose-derived aldehyde inhibitors seriously blocked the biorefinery of biofuels and biochemicals. To date, the economic production of lignocellulose-based products heavily relied on high productivities of fermenting strains. However, it was expensive and time-consuming for the achievable rational modification to strengthen stress tolerance robustness of aldehyde inhibitors. Here, it aimed to improve aldehyde inhibitors tolerance and cellulosic bioethanol fermentability for the chassis Zymomonas mobilis ZM4 pretreated using energy-efficient and eco-friendly cold plasma.

RESULTS

It was found that bioethanol fermentability was weaker in CSH (corn stover hydrolysates) than that in synthetic medium for Z. mobilis, and thus was attributed to the inhibition of the lignocellulose-derived aldehyde inhibitors in CSH. Convincingly, it further confirmed that the mixed aldehydes severely decreased bioethanol accumulation through additional aldehydes supplementary assays in synthetic medium. After assayed under different processing time (10-30 s), discharge power (80-160 W), and working pressure (120-180 Pa) using cold atmosphere plasma (CAP), it achieved the increased bioethanol fermentability for Z. mobilis after pretreated at the optimized parameters (20 s, 140 W and 165 Pa). It showed that cold plasma brought about three mutation sites including ZMO0694 (E220V), ZMO0843 (L471L) and ZMO0843 (P505H) via Genome resequencing-based SNPs (single nucleotide polymorphisms). A serial of differentially expressed genes (DEGs) were further identified as the potential contributors for stress tolerance via RNA-Seq sequencing, including ZMO0253 and ZMO_RS09265 (type I secretion outer membrane protein), ZMO1941 (Type IV secretory pathway protease TraF-like protein), ZMOr003 and ZMOr006 (16S ribosomal RNA), ZMO0375 and ZMO0374 (levansucrase) and ZMO1705 (thioredoxins). It enriched cellular process, followed by metabolic process and single-organism process for biological process. For KEGG analysis, the mutant was also referred to starch and sucrose metabolism, galactose metabolism and two-component system. Finally, but interestingly, it simultaneously achieved the enhanced stress tolerance capacity of aldehyde inhibitors and bioethanol fermentability in CSH for the mutant Z. mobilis.

CONCLUSIONS

Of several candidate genetic changes, the mutant Z. mobilis treated with cold plasma was conferred upon the facilitated aldehyde inhibitors tolerance and bioethanol production. This work would provide a strain biocatalyst for the efficient production of lignocellulosic biofuels and biochemicals.

Enhancing enzymatic saccharification of sunflower straw through optimal tartaric acid hydrothermal pretreatment

Sunflower straw, a usually neglected and abundant agricultural waste, has great potential for contributing to environmental protection realizing its high-value of valorization if utilizing properly. Because hemicellulose contains amorphous polysaccharide chains, relatively mild organic acid pretreatment can effectively reduce its resistance. Through hydrothermal pretreatment, sunflower straw was pretreated in tartaric acid (1 wt%) at 180 ^oC for 60 min to enhance its reducing sugar recovery. After tartaric acid-assisted hydrothermal pretreatment, 39.9% of lignin and 90.2% of hemicellulose were eliminated. The reducing sugar recovery increased threefold, while the solution could be effectively reused for four cycles. The properties of more porous surface, improved accessibility, and decreased surface lignin area of sunflower straw were observed through various characterizations, which explained the improved saccharide recovery and provided a basis for the mechanism of tartaric acid-assisted hydrothermal pretreatment. Overall, this tartaric acid hydrothermal pretreatment strategy greatly provided new impetus for the biomass refinery.

Enhancing enzymatic hydrolysis of waste sunflower straw by clean hydrothermal pretreatment

Hydrothermal pretreatment is an effective way to change the lignocellulose structure and improve its saccharification. An efficient hydrothermal pretreatment of sunflower straw was conducted when the severity factor (LogR0) was 4.1. 60.4% of xylan and 36.5% of lignin were removed at 180 ℃ for 120 minutes with a solid-to-liquid ratio of 1:15. A series of characterizations (such as X-ray diffraction, Fourier Transform infrared spectroscopy, scanning electron microscopy, chemical component analysis, cellulase accessibility) proved that hydrothermal pretreatment destroyed sunflower straw surface structure, enlarged its pores, and enhanced the accessibility to cellulase (371.2 mg/g). After the enzymatic saccharification of treated sunflower straw for 72 h, 68.0% yield of reducing sugar and 61.8% yield of glucose were achieved, and 4.0 g/L xylo-oligosaccharide was obtained in the filtrate. Overall, this easy-to-operate and green hydrothermal pretreatment could effectively destroy the surface barrier of lignocellulose, help remove lignin and xylan, and increase the enzymatic hydrolysis efficiency.

Improved production of adipic acid from a high loading of corn stover via an efficient and mild combination pretreatment

Adipic acid is one kind of important organic dibasic acid, which has crucial role in manufacturing plastics, lubricants, resins, fibers, etc. Using lignocellulose as feedstock for producing adipic acid can reduce production cost and improve bioresource utilization. After pretreated in the mixture of 7 wt% NaOH and 8 wt% ChCl-PEG10000 at 25 ^oC for 10 min, the surface of corn stover became loose and rough. The specific surface area was increased after the removal of lignin. A high loading of pretreated corn stover was enzymatically hydrolyzed by cellulase (20 FPU/g substrate) and xylanase (15 U/g substrate), and the yield of reducing sugars was as high as 75%. Biomass-hydrolysates obtained by enzymatic hydrolysis were efficiently fermented to produce adipic acid, and the yield was 0.45 g adipic acid per g reducing sugar. A sustainable approach for manufacturing adipic acid from lignocellulose via a room temperature pretreatment has great potential in future.