Saccharification Rate Research Articles

Effect of integrated treatment on enhancing the enzymatic hydrolysis of cocksfoot grass and the structural characteristics of co-produced hemicelluloses

BackgroundCocksfoot grass (Dactylis glomerata L.) with high biomass yield and rich cellulose can be used to produce bioethanol as fuel additive. In view of this, ultrasonic and hydrothermal pretreatments followed by successive alkali extractions were assembled into an integrated biorefinery process applied on cocksfoot grass to improve its enzymatic hydrolysis. In this work, the effects of ultrasonic and hydrothermal pretreatments followed by sequential alkali extractions on the enzymatic hydrolysis of cocksfoot grass were investigated. In addition, since large amount of hemicelluloses were released during the hydrothermal pretreatment and alkali extraction process, the yields, structural characteristics and differentials of water- and alkali-soluble hemicellulosic fractions isolated from different treatments were also comparatively explored.ResultsThe integrated treatment significantly removed amorphous hemicelluloses and lignin, resulting in increased crystallinity of the treated residues. A maximum saccharification rate of 95.1% was obtained from the cellulose-rich substrate after the integrated treatment. In addition, the considerable hemicelluloses (31.4% water-soluble hemicelluloses and 53.4% alkali-soluble hemicelluloses) were isolated during the integrated treatment. The released water-soluble hemicellulosic fractions were found to be more branched as compared with the alkali-soluble hemicellulosic fractions and all hemicellulosic fractions were mixed polysaccharides mainly composed of branched xylans and β-glucans.ConclusionThe combination of ultrasonic and hydrothermal pretreatments followed by successive alkali extractions can dramatically increase the enzymatic saccharification rate of the substrates and produce considerable amounts of hemicelluloses. Detailed information about the enzymatic hydrolysis rates of the treated substrates and the structural characteristics of the co-produced hemicelluloses will help the synergistic utilization of cellulose and hemicellulose in cocksfoot grass.

Enhancement of lignin removal and enzymolysis of sugarcane bagasse by ultrasound-assisted ethanol synergized deep eutectic solvent pretreatment

A low-cost and green biorefinery will increase the economy and revenue from lignocellulosic biomass. This study demonstrated the effect of two-pot sequential pretreatment, comprising of ultrasound ethanol (USEL) synergized ternary deep eutectic solvent (TDES, choline chloride: glycerol: FeCl3·6H2O), with the aim to investigate the effects of USEL, TDES, and USEL + TDES pretreatments on enhancing delignification of sugarcane bagasse (SCB). The results showed that under the optimum TDES pretreatment conditions (FeCl3·6H2O, 120 °C, 3 h), the cellulose content and lignin removal rate (LRR) of SCB reached 47.67 and 82.71%, respectively. Under the optimum synergy conditions (USEL conditions: 100% ethanol, 20 + 28 + 40 kHz, 240 W, 60 min; TDES conditions: FeCl3·6H2O, 120 °C, 3 h), the cellulose content and LRR of SCB reached 66.17 and 86.39%, respectively. After enzymatic hydrolysis, the SCB pretreated with USEL + TDES shows a saccharification rate of 90.31%, which was substantially higher than that of the SCB pretreated with TDES alone (85.68%). X-ray diffraction, particle size, brunauer-emmet-teller, scanning electron microscopy, and optical microscopy analyses were conducted to confirm the efficiency of USEL + TDES on pretreating SCB. Meanwhile, 2D-HSQC NMR analysis revealed that regenerated lignin exhibited well-preserved structures (β-O-4, β-β linkages), making it suitable for depolymerization into monoaromatic compounds. Overall, this work demonstrated that biomass pretreatment with the USEL + TDES was promising for a low-cost biorefinery to efficiently fractionate lignocellulosic biomass into glucose and high-quality lignin with tailored chemical structures.

Applying Molecular Phenotyping Tools to Explore Sugarcane Carbon Potential.

Sugarcane (Saccharum spp.), a C4 grass, has a peculiar feature: it accumulates, gradient-wise, large amounts of carbon (C) as sucrose in its culms through a complex pathway. Apart from being a sustainable crop concerning C efficiency and bioenergetic yield per hectare, sugarcane is used as feedstock for producing ethanol, sugar, high-value compounds, and products (e.g., polymers and succinate), and bioelectricity, earning the title of the world’s leading biomass crop. Commercial cultivars, hybrids bearing high levels of polyploidy, and aneuploidy, are selected from a large number of crosses among suitable parental genotypes followed by the cloning of superior individuals among the progeny. Traditionally, these classical breeding strategies have been favoring the selection of cultivars with high sucrose content and resistance to environmental stresses. A current paradigm change in sugarcane breeding programs aims to alter the balance of C partitioning as a means to provide more plasticity in the sustainable use of this biomass for metabolic engineering and green chemistry. The recently available sugarcane genetic assemblies powered by data science provide exciting perspectives to increase biomass, as the current sugarcane yield is roughly 20% of its predicted potential. Nowadays, several molecular phenotyping tools can be applied to meet the predicted sugarcane C potential, mainly targeting two competing pathways: sucrose production/storage and biomass accumulation. Here we discuss how molecular phenotyping can be a powerful tool to assist breeding programs and which strategies could be adopted depending on the desired final products. We also tackle the advances in genetic markers and mapping as well as how functional genomics and genetic transformation might be able to improve yield and saccharification rates. Finally, we review how “omics” advances are promising to speed up plant breeding and reach the unexplored potential of sugarcane in terms of sucrose and biomass production.

Cloning, characterization of a novel acetyl xylan esterase, and its potential application on wheat straw utilization

Acetyl xylan esterases are among the key enzymes in the xylan degradation enzyme system. However, acetyl xylan esterases from natural microorganisms have low expression and low enzyme activity and are impure. In this study, a new xylanase gene, est1051, from the metagenomic library, was expressed in the prokaryotic system. Its enzymatic properties were explored, including optimum temperature and pH, thermal and pH stability, and tolerance against organic solvents, metal ions and salt solutions. Then the fermentation conditions of EST1051 were optimized by the response surface method, and the maximum enzyme yield reached 1909.32 U/L. Finally, the synergism with cellulase on straw degradation was evaluated. EST1051 displays high homology with acetylxylan esterases in terms of amino acid sequences and conserved active sites. EST1051 shows high stability across a broad temperature range, and retains more than 60% of its enzymatic activity between 4 and 60°C after 24 h of incubation. Single-factor analysis and orthogonal design were conducted to determine the optimal conditions for the maximizing the saccharification rate of wheat straws. Interestingly, the synergism of EST1051 with cellulase contributes to the efficient transformation of wheat straws. These findings may open the door to significant industrial applications of this novel acetylxylan esterase.

Efficient Saccharification of Ionic Liquid-Pretreated Rice Straw in a One-Pot System Using Novel Metagenomics Derived Cellulases

Ionic liquids (ILs)-resistant cellulase enzymes can facilitate the saccharification of IL-pretreated biomass in a one-pot wash-free method. Using a bioinformatics approach, two cellulases, Persicel7 and Persicel8, with convincing evidence for ion liquid tolerance were identified. Subsequently, these enzymes were heterologously expressed and biochemically characterized. Persicel7 and Persicel8 exhibited endo-β-1, 4-glucanase activity and were resistant to inhibitors and several organic solvents. Thier activity in 10% (v/v) 1-Ethyl-3-methylimidazolium chloride and 1-Butyl-3-methylimidazolium chloride were higher than 130%, as compared with IL-free control. The half-life of cellulases improved up to 11-fold when incubated with 20% (v/v) solution of ion liquids. A one-pot IL-pretreatment and enzymatic saccharification process based on Persicel7 and Persicel8 were established. By this process, the saccharification rate of rice straw was enhanced by 33% versus the untreated reaction. The Persicel7 and Persicel8 unique properties make them attractive candidates for industrial applications, particularly hydrolyzing ion liquid activated biomass in a one-pot system.

Development of a process for the enhanced enzymatic digestibility of solid waste from tofu to yield fermentable biosugars

Tofu solid waste (TSW), an abundant agricultural waste product from the soy industry, can be used as an excellent source of renewable biomass by the action of microbes, indicating a better utilization prospect as opposed to its disposal in landfills or being incinerated. In this study, the composition of TSW was investigated. The waste material was used to produce lactic acid by enzymatic saccharification and fermentation using Bacillus sp. NL01. TSW was determined to be rich in carbohydrates and protein, and could, therefore, be used as a nutrient to facilitate microbial growth. Without pre-treatment, a maximum glucan saccharification rate of 91.6% was achieved by using a mixture of cellulase CTec2 and hemicellulose H2125. Using 1000 g dry weight of TSW as the starting material, 160 g of glucose was recovered and subsequently used to yield 150 g of lactic acid by the action of Bacillus sp. NL01. Thus, the method developed in this study was effective in the production of lactic acid from TSW and can likely provide a deeper insight into the utilization of TSW in biorefineries.

Optimizing the saccharification of pretreated wood biomass using crude enzyme from Acanthophysium sp. KMF001

This study was conducted on crude enzyme from the novel strain Acanthophysium sp. KMF001 using a mediator (surfactant). The surfactant was applied to the steam-exploded pretreated domestic wood biomass, and response surface methodology (RSM) was conducted to determine the optimum conditions for saccharification using the optimum substrate concentration, enzyme concentration, and surfactant concentration. Steam-explosion of Korean oak (25 kgf/cm2) for 7 min showed a maximum-predicted saccharification of approximately 99.9% at 7.0% substrate concentration, 37.5 FPU (filter paper units) enzyme concentration, and 475.8 mg/g-glucan surfactant (polysorbate 80) concentration. Steam-explosion of red pine (25 kgf/cm2) for 7 min revealed a maximum prediction saccharification rate of approximately 58.7% at 6.5% substrate concentration, 36.3 FPU enzyme concentration, and 330.3 mg/g-glucan surfactant (polysorbate 80) concentration. The extents of saccharification of Korean oak (99.9%) and pine (58.7%) demonstrated the high applicability of the crude enzyme from Acanthophysium sp. KMF001.

A study on different parameters affecting the saccharification rate of Typha orientalis pretreated with Ionic Liquids (ILs) and microwave irradiation for bioethanol production by using response surface methodology

This study investigates the saccharification rate of Typha orientalis pretreated with Ionic liquids 4-(3-Methyl−1-imidazolio) − 1-butanesulfonic acid hydrogen sulfate [BSO3HMIM] [HSO4], combined with microwave irradiation for liquid biofuel production. Methods of full factorial experimental design was used to explore the factors affecting the conversion rate of fibers into fermentable sugar. The results from Plackett-Burman Design (PBD) shows that efficiency on the saccharification rate of Typha orientalis was in the order of microwave power > solvent volume > catalyst > reaction time. From the results obtained, optimum parameter was determined by Central Composite Design (CCD) where the highest saccharification rate attained was 52.9%.

Effects of residual lignin and cellulose swelling on the rate of enzymatic saccharification of softwood and hardwood acid sulfite pulps

We estimated the effect of residual lignin and pulp swelling on the rate of enzymatic saccharification to increase production of ethanol from acid sulfite pulp (SP) by means of enzymatic treatment. The resolution ratio of hardwood (Acacia mearnsii) SP after the enzymatic treatment was lower compared to softwood (Larix leptolepis) SP even though lignin content of hardwood SP was lower. The pyrolysis–gas chromatography/mass spectrometry (Py-GC/MS) analysis revealed that the residual lignin in hardwood SP could more easily adsorb enzyme compared to softwood SP, and the residual lignin in hardwood SP should interfere with the binding of the enzyme to cellulose. The beating treatment of pulp increased the swelling of pulp. The enzymatic saccharification rate was increased by the beating treatment. On the other hand, the delignification treatment was more effective than the beating treatment at enhancing enzymatic saccharification of both hardwood and softwood SPs. We found that the delignification process should be considered a high-priority technique for enhancing enzymatic saccharification of SP.

Circular economy in olive oil production – Olive mill solid waste to ethanol and heavy metal sorbent using microwave pretreatment

Olive mill solid waste (OMSW) is an abundant agricultural waste without viable solution. The effects of OMSW different pretreatments (microwave or autoclave), different additives (water, formic, or sulfuric acid), and utilization of different saccharification enzymes (Cellic® CTec2 or Accellerase® 1500) were tested on saccharification process and sugar release, and on fermentation inhibitors formation and ethanol production. Microwave treatment with formic acid resulted in highest saccharification rates (90% of cellulose fraction) and fermentation yields (15.9 g/L ethanol), although loss of sugars and fermentation inhibitors production was notable. Microwave with water treatment resulted in less saccharification and ethanol (9.6 g/L). To facilitate economical process and to extract maximum value, solid remnants after saccharification were tested as heavy metal sorbent. Microwave with water resulted in the best sorbent, followed by microwave with formic acid. Addition of sulfuric acid, to either microwave or autoclave, resulted in very poor saccharification and absorbance capacity. Therefore, combination of ethanol and sorbent production from OMSW are suggested.

Characterization of ultrasonic-treated corn crop biomass using imaging, spectral and thermal techniques: a review

The corn crop biomass (CB) is widely used as a feedstock for biochemicals such as lactic acid, succinic acid, citric acid, xanthan gum, and biofuels likely bioethanol, butanol, and biogas. Since CB provides a resistive structure for enzymatic and microbial attack, ultrasonic treatment can assist to break the recalcitrance structure. Several techniques such as imaging (atomic force microscopy—AFM; scanning electron microscopy—SEM), spectroscopy (energy-dispersive X-ray spectroscopy—EDX; Fourier transform infrared spectroscopy—FTIR; Raman spectroscopy; X-ray diffraction—XRD), and thermal (TGA) were studied to characterize the ultrasonicated CB. A detailed analysis of different techniques on their potential benefits will assist the researchers to select a suitable technique to optimize the ultrasonication for various applications. The basic mechanisms behind ultrasonication, benefits, downsides, practical considerations, and factors that should be deliberated in the future studies are discussed. Sonication enhanced the hemicellulose and cellulose yield, saccharification rate, and delignification of CB. AFM, EDX, FTIR, Raman spectroscopy, SEM, TGA, and XRD described the variations in topographical features, elemental composition, molecular structure, microstructure, thermal steadiness, and degree of crystallinity, respectively, of the ultrasonicated CB. The quantitative crystallinity of CB can be analyzed through XRD and Raman spectroscopy, whereas the qualitative crystallinity and molecular structural comparisons are studied using FTIR. Imaging techniques can provide important aspects such as lignin relocalization and cell wall delamination. Integrating EDX with SEM is beneficial to determine the elemental percentage composition altered in CB due to ultrasonication.

Demonstration‐scale enzymatic saccharification of sulfite‐pulped spruce with addition of hydrogen peroxide for LPMO activation

AbstractThe saccharification of lignocellulosic materials like Norway spruce is challenging due to the recalcitrant nature of the biomass, and it requires optimized and efficient pretreatment and enzymatic hydrolysis processes to make it industrially feasible. In this study, we report successful enzymatic saccharification of sulfite‐pulped spruce (Borregaard's BALI™ process) at demonstration scale, achieved through the controlled delivery of hydrogen peroxide (H2O2) for the activation of lytic polysaccharide monooxygenases (LPMOs) present in the cellulolytic enzyme preparation. We achieved 85% saccharification yield in 4 days using industrially relevant conditions – that is, an enzyme dose of 4% (w/w dry matter of substrate) of the commercial cellulase cocktail Cellic CTec3 and a substrate loading of 12% (w/w). Addition of H2O2 and the resulting controlled and high LPMO activity had a positive effect on the rate of saccharification and the final sugar titer. Clearly, the high LPMO activity was dependent on feeding the reactors with the LPMO co‐substrate H2O2, as in situ generation of H2O2 from molecular oxygen was limited. These demonstration‐scale experiments provide a solid basis for the use of H2O2 to improve enzymatic saccharification of lignocellulosic biomass at large industrial scale.© 2020 The Authors. Biofuels, Bioproducts, and Biorefining published by Society of Chemical Industry and John Wiley & Sons, Ltd.

Process optimization for chemical pretreatment of rice straw for bioethanol production

Pretreatment of rice straw was optimized by physical and chemical methods. Among all the pretreatment methods followed by saccharification, autoclaved ammonia pretreatment significantly enhanced the liberation of reducing sugars i.e. 233.76 ± 1.23 mg/g substrate as compared to other methods. Further statistical optimization by response surface methodology (RSM) including ammonia concentration, substrate concentration and autoclaving time, enhanced the saccharification rate by 1.9-fold i.e. 451.96 mg/g substrate at 5 % rice straw, 12 % ammonia and autoclave time of 30 min after saccharification of 6 h. Maximum liberation of reducing sugars (635.37 mg/g substrate) was attained under these optimized conditions at 60 °C after 48 h. Fourier-transform infrared spectroscopy, X-ray diffraction and scanning electron microscope analysis clearly confirmed the removal of lignin in pretreated biomass. Ammonia pretreated enzymatic hydrolysate was fermented by Saccharomyces cerevisiae at 30 °C, pH 7.0, 150 rpm and 20 % hydrolysate, resulted in 24.37 g/L bioethanol after 72 h.

Extrusion process to enhance the pretreatment effect of ionic liquid for improving enzymatic hydrolysis of lignocellulosic biomass

Extrusion process using 1-ethyl-3-methylimidazolium acetate ([EMIM]Ac) in co-solvent, dimethyl sulfoxide (DMSO), was conducted to improve the pretreatment effect on the enzymatic saccharification of pussy willow (Salix gracilistyla Miq.). The use of a twin screw extruder capable of continuous processing increased the solid loading to 50% in [EMIM]Ac and its co-solvent DMSO. The water-soluble fraction was increased by increasing the [EMIM]Ac amount in co-solvent and the extrusion temperature but decreasing the screw rotating speed and solid loading. The surface morphologies of the extruded product showed remarkable disruption of the cell wall structures and fibrillation with increasing amounts of [EMIM]Ac in co-solvent. With increasing [EMIM]Ac amount in co-solvent and extrusion temperature and with decreasing screw rotating speed and solid loading, the crystalline structure of cellulose was more disrupted, resulting in the increase in saccharification yield. The highest yield of glucose and xylose was 99.0% and 99.5%, respectively, from the pretreated products using only [EMIM]Ac under solid loading of 15% at 160 °C extrusion temperature and 5 rpm screw rotating speed. The initial saccharification rate was faster in the pretreated product precipitated in alcohol and acetone than in water.

Cloning and characterization of low-temperature adapted GH5-CBM3 endo-cellulase from Bacillus subtilis 1AJ3 and their application in the saccharification of switchgrass and coffee grounds

Endocellulase is a key cellulase for cellulosic material pretreatment in the industry by hydrolyzing long cellulose chains into short chains. To investigate the endocellulase characteristics from Bacillus subtilis 1AJ3, and increase its production yield, this paper cloned an endocellulase gene denoted CEL-5A from strain 1AJ3 and expressed in E. coli BL21 (DE3). The CEL-5A gene was sequenced with a full-length of 1500 bp, encoding a totally of 500 amino acids, and containing two domains: the GH5 family catalytic domain (CD) and the CBM3 family cellulose-binding domain (CBD). Recombinant endocellulase Cel-5A with a His-tag was purified of the Ni-NTA column, and SDS-PAGE results demonstrated that Cel-5A exhibited a molecular weight of 56.4 kDa. The maximum enzyme activity of Cel-5A was observed at pH 4.5 and 50 °C. Moreover, it was active over the broad temperature region of 30–60 °C, and stable within the pH range of 4.5–10.0. In addition, Co2+ was able to increase enzyme activity, while the majority of metal ions demonstrated stable enzyme activity under low- concentration. The substrate specificity of Cel-5A exhibited a high specific activity on the β-1,3-1,4 glucan linkage from barley. The Michaelis–Menten constant and the maximum velocity of the recombinant Cel-5A for CMC-Na were determined as 14.87 mg/mL and 19.19 μmol/min/mg, respectively. When Cel-5A was applied to the switchgrass and coffee grounds, its color became lighter and the biomass was observed to loosen following hydrolyzation. The saccharification rate reached 12% of the total weight of switchgrass in 20 h. These properties highlight the potential application of Cel-5A as an endocellulase in the pretreatment of biomass, for example, in the coffee grounds/waste, and related industries.

Isolation of Thermostable Lignocellulosic Bacteria From Chicken Manure Compost and a M42 Family Endocellulase Cloning From Geobacillus thermodenitrificans Y7.

The composting ecosystem provides a potential resource for finding new microorganisms with the capability for cellulose degradation. In the present study, Congo red method was used for the isolating of thermostable lignocellulose-degrading bacteria from chicken manure compost. A thermophilic strain named as Geobacillus thermodenitrificans Y7 with acid-resident property was successfully isolated and employed to degrade raw switchgrass at 60°C for 5 days, which resulted in the final degradation rates of cellulose, xylan, and acid-insoluble lignin as 18.64, 12.96, and 17.21%, respectively. In addition, GC-MS analysis about aromatic degradation affirm the degradation of lignin by G. thermodenitrificans Y7. Moreover, an endocellulase gene belong to M42 family was successfully cloned from G. thermodenitrificans Y7 and expressed in Escherichia coli BL21. Recombinant enzyme Cel-9 was purified by Ni-NTA column based the His-tag, and the molecular weight determined as 40.4 kDa by SDA–PAGE. The characterization of the enzyme Cel-9 indicated that the maximum enzyme activity was realized at 50°C and pH 8.6 and, Mn2+ could greatly improve the CMCase enzyme activity of Cel-9 at 10 mM, which was followed by Fe2+ and Co2+. Besides, it also found that the β-1,3-1,4, β-1,3, β-1,4, and β-1,6 glucan linkages all could be hydrolyzed by enzyme Cel-9. Finally, during the application of enzyme Cel-9 to switchgrass, the saccharification rates achieved to 1.81 ± 0.04% and 2.65 ± 0.03% for 50 and 100% crude enzyme, respectively. All these results indicated that both the strain G. thermodenitrificans Y7 and the recombinant endocellulase Cel-9 have the potential to be applied to the biomass industry.

Structural changes in sugarcane bagasse cellulose caused by enzymatic hydrolysis

Cellulose I is not completely saccharified to glucose at a low cellulase concentration. In this study, sugarcane cellulose saccharification residues were investigated. Transmission electron microscopy images indicated that the cellulose microfibrils became shorter in the early stages of saccharification and gradually became narrower. The degree of polymerization also decreased in the early stages of saccharification. Cellulose saccharification residues were deuterated by immersing them in deuterium oxide. Infra-red spectra of the deuterated residues indicated that the deuterated hydroxyl group ratio decreased as saccharification progressed. This indicated that cellulose microfibrils were hydrolyzed in their hydrophobic planes by cellulase as if the surfaces were scraped. The increase of hydrophobic planes caused microfibril aggregation, poor accessibility of cellulase to the microfibrils, and a low saccharification rate.

Enhancement of converting corn stalk into reducing sugar by ultrasonic-assisted ammonium bicarbonate pretreatment

In order to improve the yield of reducing sugar from corn stalk, ultrasonic-assisted ammonium bicarbonate pretreatment of corn stalk was proposed. Three ultrasonic factors (time (0–30 min), temperature (30–60 °C) and liquid/solid mass ratio (5–20)) were optimized by response surface experiment. The optimal conditions of ultrasonic pretreatment were obtained (liquid/solid mass ratio is 12:1, temperature is 42 °C and time is 11 min). The highest saccharification rate of corn stalk was of 82.61%, which was remarkably increased by 355% compared to the control group.

Extracellular hydrolytic enzyme activities of indigenous actinomycetes on pretreated bagasse using choline acetate ionic liquid

Abstract Ionic liquids (ILs) pretreatment is currently becoming an attractive approach for improving the efficiency of enzymatic hydrolysis on lignocellulose. Cholinium acetate (ChOAc) ILs that contain choline cation combined with carboxylic acid-based anion is not only marked as biocompatible ILs but also known as a useful catalyst in the pretreatment of lignocellulosic biomass, which results in an increase of enzymatic saccharification rate of the biomass. In this study hydrolytic activities of cellulase and xylanase which produce extra-cellularly by isolated actinomycetes under the presence of ChOAc were investigated. ChOAc/biomass ratio (g/g) were set up between 0.0 and 3.0 for pretreatment followed by hydrolysis using cellulase and xylanase that excreted when actinomycetes were grown up in pretreated bagasse successively. Act-7 was used as inoculum in saccharification, and the optimum of ChOAc/biomass ratio was as identified to be 1, which achieved high saccharification with a yield of reducing sugar 74.58%. Since the cellulase activities reduced to around 30–70% while ChOAc/biomass ratio was increased to 2–3, in contrast, xylanase activities remain stable at the range of 58.97–75.19 U/mL. This experiment demonstrates the promising bio-hydrolysis of biomass in green technology to increase the yield of the biomass saccharification process.

Effect of various pretreatments on improving cellulose enzymatic digestibility of tobacco stalk and the structural features of co-produced hemicelluloses

Hereon, tobacco stalk was deconstructed by lyophilization, ball-milling, ultrasound-assisted alkali extraction, hydrothermal pretreatment (HTP), and alkali presoaking, respectively, followed by dilute alkali cooking to both improve its enzymatic digestibility and isolate the hemicellulosic streams. It was found that a maximum cellulose saccharification rate of 93.5% was achieved from the integrated substrate by ball-milling and dilute alkali cooking, which was 4.4-fold higher than that from the raw material. Interestingly, in this case, 76.9% of hemicelluloses were simultaneously recovered during the integrated treatment. Structural determination indicated that the hemicelluloses released from tobacco stalk by dilute alkali cooking were mixed polysaccharides, and the (1 → 4)-linked β-D-Xylp backbone branched with L-Araf units at O-2/O-3 and 4-O-Me-α-D-GlcpA units at O-2 of the xylose residues was the main structure. In comparison, ultrasound-assisted alkali extraction, ball-milling, and HTP favored the extraction of hemicelluloses with less branched structure and lower molecular weights in the following alkali cooking.