Xylose Yield Research Articles

Investigation on Nitrogen Migration and Transformation during Hydrothermal Conversion of Glucose and Xylose in N-rich Solution Recycled from Hydrothermal treatment of Fiberboard

Nitrogen migration and transformation have been extensively studied during the thermochemical conversion of biomass, particularly N-rich biomass, due to concerns about nitrogen oxides pollution or the preparation of N-doped carbon materials. Nitrogen in fiberboard was extracted into an aqueous solution through low-temperature hydrothermal treatment to prepare the recycled aqueous solution. Subsequently, hydrothermal conversions of glucose and xylose were conducted in the recycled solution. The migration and transformation of nitrogen between hydrochars and aqueous phase were investigated. The results showed that the nitrogen retention rates of glucose hydrochars were higher than those of xylose hydrochars at low temperatures. As the temperature increased, the nitrogen retention rates of glucose and xylose hydrochars tended to converge, reaching their highest value at 220 °C. In hydrochars, nitrogen had a high content and was widely distributed on the surface of the carbon microspheres. The nitrogen content did not change significantly with increasing temperatures, but the nitrogen functional groups tended to become more thermostable. In addition, the char yields of glucose and xylose in fiberboard recycled solution were significantly higher than that in the ultrapure water at low temperatures, which indicates that the introduction of nitrogen promotes the formation of hydrochars. These findings favored the study on the nitrogen migration and transformation during hydrothermal conversions of lignocellulose in a N-rich environment.

A novel homologous acid ferric chloride/5-sulfosalicylic acid coordinated catalytic pretreatment for high-efficiency selective separation of poplar hemicellulose

The selective and efficient separation of hemicellulose is a challenge for utilizing lignocellulosic biomass for high-value purposes. This study reports the development of a novel homogeneous acid-catalyzed pretreatment technique based the homologous action of both FeCl3 and 5-sulfosalicylic acid (5-SAA). The optimal separation conditions (5-SAA concentration of 7.0 %, reaction temperature of 130 °C, FeCl3 concentration of 0.15 mol·L−1, and reaction time of 60 min) enabled a high hemicellulose separation efficiency of 90.68 %. The hemicellulose-derived total sugar yield was as high as 83.05 % which was increased by 30 %. Moreover, the xylose yield was increased by 10 %, and the content of oligosaccharides was triple higher than that in the single component treatment, up to 19.64 %. The depolymerization and recondensation of lignin were prevented using the 5-SAA hydrophobic structure (benzene ring structure) and hydrophilic end (−HSO3 and −COOH). The proposed strategy is a promising approach that can enable an efficient and selective separation of hemicellulose and consequently improve the quality of biomass materials.

Novel self-pretreatment of biomass by in-situ preparation of acid-assisted carbohydrate-derived DES

Deep eutectic solvents (DES) can greenly and efficiently fractionate biomass, but their utilization efficiency is severely limited by the high ratio of DES required and the wasted hemicelluloses released during the pretreatment. Herein, this work first developed a novel self-pretreatment of biomass by in-situ preparation of acid-assisted carbohydrate-derived DES with the aid of ball milling to facilitate enzymatic hydrolysis. The effect of hydrogen bond acceptor types, water content, acid content, and ball-milling time on enzymatic hydrolysis was studied systematically. Under the optimal condition (tetrabutylammonium chloride (TBAC), 1000 wt% H2O, 100 wt% acids, ball milling for 2 h), the yields of glucose and xylose produced from the pretreated substrates after enzymatic hydrolysis were >99.9 % and 88 %, respectively. Furthermore, the structural integrity of the residual lignin was well-preserved, making it suitable for positional structural characterization and ideal substrates for lignin degradation. Characterization suggested that the hemicelluloses fragments via in-situ acid hydrolysis acted as hydrogen bond donors and combined in situ with TBAC to form DES. This strategy avoided the use of high dosages of DES and the wastage of hemicelluloses, and promoted the sustainability of the entire biorefinery process.

Xylitol production by Barnettozyma populi Y-12728 with different immobilization strategies

One of the new xylitol producer microorganisms is Barnettozyma populi Y-12728 and it has great potential for the industry with its pure xylitol production capability. Different immobilization strategies, the usability of baffled or normal flasks with different agitation speeds, and various lignocellulosic hydrolysates were studied in this research. The highest xylitol production and yield values were 11.99 g xylitol/L and 40.28 % for the C1 trial at 70 ml medium with a suspended cell. For the immobilization strategy, 1 % polyethyleneimine concentration, 1.5 mm surface lattice thicknesses, and 8 3D cubes were determined to be the optimum conditions with 17.84 g/L xylitol production and 0.473 g xylitol/g xylose yield values in a 70 ml volume medium at 200 rpm, 30 °C, and 6.0 initial pH for 3 days. Rice husk, wheat bran, and oat husk hydrolysates were also used as a substrate for xylitol fermentation. The highest xylitol production was 2.26 g/L for lignocellulosic hydrolysates. In this research, FDM (Fused Deposition Modelling) based 3D printed cubes are used for the immobilization agent of Barnettozyma populi NRRL Y-12728 for the first time. The results revealed that FDM-based 3D-printed cubes could be used to immobilize cells and improve productivity for xylitol production.

Utilization of cotton stalk waste for sustainable isopropanol production via hydrolysis and coculture fermentation

The present investigation focused on isopropanol production from lignocellulosic cotton stalk biomass (CSB) using conventional pretreatment, enzymatic hydrolysis and fermentation methods. In comparison to alkaline (NaOH) pretreatment, dilute sulphuric acid (H2SO4) pretreatment showed higher cellulose exposure (448.5 mg/g). Further, ultrasono assisted acid and alkali pretreatment was performed for maximum exposure of cellulose and it was found 616.9 and 586.15 mg/g respectively. Chemical pretreated CSB was additionally exposed to independent enzymatic hydrolysis using commercial enzymes (Celluclast and Viscozymes) following Response Surface Methodology (RSM), which revealed a maximal production of glucose and xylose yield (544.6 mg/g and 41.8 mg/g). Pretreated and enzymatic hydrolyzed cotton stalk biomass at various conditions were analysed using SEM, FTIR, and XRD to determine the structural and functional changes. Further, a co-culture strategy was employed on pretreated and hydrolyzed CSB using two fermented yeast strains (Saccharomyces cerevisiae and Pichia pastoris) for isopropanol production. HR-MS analysis revealed that the maximum concentration of isopropanol (126.228 mM) was produced in 2:1 proportionate ratio of two fermented yeasts with 20 g/L of substrate loadings at 72 h of incubation time. These results indicate that the production of isopropanol (7.46 g/L) from CSB with different parametric conditions is an encouraging step and can be exploited further for various industrial applications.

Application of In-House Xylanases as an Addition to a Commercial Cellulase Cocktail for the Sustainable Saccharification of Pretreated Blue Agave Bagasse Used for Bioethanol Production

The study involves the use of commercial cellulase Cellic CTec2 in combination with two in-house xylanases, PxXyn10A (XynA), a recombinant purified enzyme from Paenibacillus xylanivorans A59, and a xylanase enzymatic extract from native Moesziomyces aphidis PYCC 5535T (MaPYCC 5535T), for the enzymatic hydrolysis of pretreated blue agave bagasse (BAB) at the high solids load of 20% (w/v). Three different combinations of cellulase and xylanases were evaluated. When Cellic® CTec2 was used at a dosage of 10 FPU/g oven-dried solids (ODS) supplemented with XynA or MaPYCC 5535T at an endo-xylanase dosage of 100 U/g ODS, increases in the xylose yield of 30% and 33%, respectively, were obtained. When applying in-house xylanases alone (at an endo-xylanase dosage of 100 U/g ODS), xylan in BAB was selectively hydrolyzed into xylose with 5% yield with MaPYCC 5535T, while no xylose was detected with XynA. Interestingly, a synergic effect of Cellic® CTec 2 with both xylanases was observed when using a low dosage of 1 FPU/g ODS (allowing for some liquefaction of the reaction mixture), promoting xylose and glucose release by either xylanase. A higher concentration of monomeric sugars was obtained with 10 FPU/g ODS of Cellic® Ctec 2 supplemented with 100 U/g ODS of MaPYCC 5535T, followed by XynA. The improvement in saccharification through the synergistic combination of in-house xylanases and commercial cellulases allows for the obtention of sugar-rich hydrolysates, which enhances the technical sustainability of the process. Hydrolysates were then fermented using recombinant Cellux 4TM yeast to yield 45 g/L ethanol, representing an increase of about 30% with respect to the control obtained with only the commercial cellulase cocktail. The surface modification of agave biomass with the different combinations of enzymes was evidenced by scanning electron microscopy (SEM).

Alcohol formaldehyde resin solid acid catalytic conversion of biomass into furan compounds

The conversion of waste lignocellulosic biomass into biomass platform chemicals is very promising. In this work, a novel resin-based solid acid catalyst was obtained by condensation of furfuryl alcohol with furfural, and mild calcination and sulfonation process. Then it was used to convert sugars and biomass to obtain furan compounds. Results showed that the solid acid with a furfural to furfuryl alcohol molar ratio of 3:1 is an irregular mesoporous material, with a specific surface area of 134.18 m2/g and an acid content of 2.723 mmol/g, which is extremely stable below 200 °C. 82.2 % (from fructose), 15.8 % (from glucose), 10.0 % (from cellobiose) yields of 5-HMF and 35.5 % (from xylose) yield of furfural could be obtained at 160 °C for 2 h. It can be reused more than 5 times and can restore the best catalytic effect after re-sulfonation. Notably, in the catalytic conversion of rice husk, rice straw, camphor tree branch and leaves under typical reaction conditions, 5-HMF and furfural was in yields of 9.4–24.5 % and 20.3–47.9 %, respectively. Moreover, a 10 % water dropwise to solvent can effectively promote the catalytic conversion of biomass, while there is a significant inhibitory effect after it exceeds 20 %.

In situ pretreatment of wood samples with deep eutectic solvents for enhanced lignin removal and enzymatic Saccharification efficiency optimization

Deep eutectic solvents (DESs) are commonly utilized as an effective pretreatment method for biomass materials, particularly for enhancing the value of lignocellulosic biomass. However, to the best of our knowledge, the utilization of DESs for in situ pretreatment of wood samples has been seldom reported. In this study, the ability of five DESs systems to in-situ pretreatment of balsa wood samples was investigated. Among of them, the Choline Chloride-Ethylene Glycol-P-Toluenesulfonic Acid (ChCl-EG-PTSA) system showing an excellent lignin removal rate (the lignin removal of 87.34 % and cellulose retention of 86.32 %), which is significantly better than the delignification effect of the traditional acid chlorite method (lignin removal of 72,13 % and cellulose retention of 64.57 %). In addition, in the subsequent enzymatic saccharification experiments, after the wood samples were pretreated in situ by the ChCl-EG-PTSA system, the enzymatic saccharification yield of cellulose reached 75.46 %, and the enzymatic saccharification yield of xylose reached 92 %. At the same time, this study also used SEM, FTIR, XPS, TGA and other testing technologies to conduct detailed analysis and characterization of the pretreated samples. This comprehensive analysis unequivocally demonstrated the viability of the ChCl-EG-PTSA system as an environmentally sustainable and efficient approach for pretreating forest biomass. Significantly, this in-situ wood pretreatment strategy significantly lays a robust research groundwork for the development of multifunctional wood fiber composites in subsequent stages.

Enhanced Production of Clean Fermentable Sugars by Acid Pretreatment and Enzymatic Saccharification of Sugarcane Bagasse

Sugarcane bagasse (SCB), an agro-industrial byproduct generated by a sugar mill, holds a substantial carbohydrate content of around 70 wt.%, comprising cellulose and hemicellulose. Saccharification plays a pivotal role in the conversion of SCB into second-generation (2G)-ethanol and valuable compounds, which is significantly aided by thermochemical pretreatments. In this study, SCB underwent diluted sulfuric acid pretreatment (2% H2SO4, 80 rpm, 200 °C, 20 min), resulting in the removal of 77.3% of the xylan. The hemicellulosic hydrolysate was analyzed to identify the sugars and degraded products acting as microbial inhibitors. The acid hydrolysate showed a xylose yield of 68.0% (16.4 g/L) and a yield of 3.8 g/L of acetic acid. Afterward, the hemicellulosic hydrolysate was concentrated 2.37 times to obtain a xylose-rich stream (39.87 g/L). The sequential detoxification, employing calcium oxide and activated carbon, removed the inhibitory compounds, including acetic acid, while preserving the xylose at 38.10 g/L. The enzymatic saccharification of cellulignin at 5% and 10% of the total solids (TSs) yielded comparable reducing sugar (RS) yields of 47.3% (15.2 g/L) and 47.4% (30.4 g/L), respectively, after 96 h, employing a 10 FPU/g enzyme loading of Cellic® CTec3 (Novozymes Inc. Parana, Brazil). In summary, these findings outline an integrated green chemistry approach aimed at addressing the key challenges associated with pretreatment, concentration, detoxification, and enzymatic hydrolysis to produce fermentable sugars.

Niobium-based single-atom catalyst promoted fractionation of lignocellulose in choline chloride-lactic acid deep eutectic solvent

Pretreatment is the key step to convert lignocelluloses to sustainable biofuels, biochemicals or biomaterials. In this study, a green pretreatment method based on choline chloride-lactic acid deep eutectic solvent (ChCl-LA) and niobium-based single-atom catalyst (Nb/CN) was developed for the fractionation of corn straw and further enzymatic hydrolysis of cellulose. With this strategy, significant lignin removal of 96.5 % could be achieved when corn straw was pretreated by ChCl-LA (1:2) DES over Nb/CN under 120 °C for 6 h. Enzymatic hydrolysis of the cellulose-enriched fraction (CEF) presented high glucose yield of 92.7 % and xylose yield of 67.5 %. In-depth investigations verified that the high yields of fractions and monosaccharides was attributed to the preliminary fractionation by DES and the deep fractionation by Nb/CN. Significantly, compared to other reported soluble catalysts, the synthesized single-atom catalyst displayed excellent reusability by simple filtration and enzymatic hydrolysis. The recyclability experiments showed that the combination of ChCl-LA DES and Nb/CN could be repeated at least three times for corn straw fractionation, moreover, the combination displayed remarkable feedstock adaptability.

Tuning Structural Characteristics of Corn Stover Through Ammonium and Sodium Sulfite (ASS) Pretreatment for Enhanced Enzymatic Hydrolysis.

The ammonia fiber expansion (AFEX) pretreatment of lignocellulosic biomass offers a significant advantage in terms of obtaining high glucan conversion, with the added benefit of ammonia being fully recyclable. However, despite the high efficiency of AFEX in pretreating lignocellulose, relatively high enzyme loading is still required for effective cellulose conversions. In this study, we have updated the AFEX pretreatment method; ammonia and sodium sulfite (ASS) can be used to produce a more digestible substrate. The results demonstrate that ASS-pretreated corn stover (CS) yields a higher fermentable sugar yield compared with AFEX pretreatment, even at lower enzyme loadings. Specifically, at an enzyme loading of 12 mg protein/g glucan, ASS-CS achieved 88.8% glucose and 80.6% xylose yield. Characterization analysis reveals that lignin underwent sulfonation during ASS pretreatment. This modification results in a more negative zeta potential for ASS-CS, indicating a reduction in nonproductive adsorption between lignin and cellulase through increased electrostatic repulsion.

Enhancing fermentable sugar production from sugarcane bagasse through surfactant-assisted ethylene glycol pretreatment and enzymatic hydrolysis: Reduced temperature and enzyme loading

In this study, an efficient coupling surfactant to ethylene glycol pretreatment (EG) and enzymatic hydrolysis of sugarcane bagasse (SCB) was proposed to enhance fermentable sugar production with lower pretreatment energy consumption and reduced enzyme loading. Under optimized conditions, 5 % Tween 80-assisted EG pretreatment of SCB achieved 80.5 % delignification while retaining cellulose (91.6 %) and hemicellulose (81.6 %) content. This led to an enhanced glucose yield of 81.3 %, compared to 65.1 % without Tween 80. The addition of Tween 80 to pretreatment modified residual lignin through etherification, reduced phenolic hydroxyl groups and enhanced hydrophilicity by 23.7 % and 9.4 %, respectively, compared to the lignin sample without Tween 80. Consequently, this modification alleviated non-productive adsorption between lignin and enzymes, improving substrate hydrolyzability. Moreover, when 4.5 % Triton-X 100 was introduced during the hydrolysis of Tween 80-assisted EG-pretreated substrates, a maximum glucose yield of 91.8 % and xylose yield of 92.6 % were achieved. Energy and enzyme cost analyses revealed a reduction of 35 % in pretreatment energy consumption and a 58.8 % decrease in enzyme costs, thanks to the synergistic action of surfactants in EG pretreatment and enzymatic hydrolysis. Overall, integrating surfactants into pretreatment and enzymatic hydrolysis holds promise for highly efficient conversion of SCB into fermentable sugars in enzyme-mediated lignocellulosic biorefineries.

Cascade fractionation of bamboo shoot shells into high-yield xylose, easily digestible cellulose and high-quality lignin nanoparticles by tailored catalytic hydrothermal–hydrated alkaline deep eutectic solvents pretreatment

The high complexity and compactness of inherent structure in lignocellulosic materials (LCM) leads to the difficulty of fractionation and conversion of its major component, which is the key obstacle limiting the value-added utilization of LCM. In this work, a cascade fractionation strategy, coupling catalytic hydrothermal pretreatment (CHTP, choline chloride: ethylene glycol: AlCl3, ChCl/ EG/ AlCl3) with hydrated alkaline deep eutectic solvent (HADES, triethylbenzyl ammonium chloride/ethanolamine, TEBAC/EM) treatment, was proposed to fractionate dendrocalamus latiftorus munro shoot shells (DLMSS). The results showed that considerably high hemicelluloses removal (94.57 %) and xylose yield (90.73 %) were achieved by the first step (CHTP, 160 °C, 1 h, 2 % of catalyst loading). The cascaded HADES treatment realized 90.25 % delignification ratio under the optimal conditions (120 °C, 3 h, 75 % of ADES loading), and the obtained residue could be easily converted into high-yield (93.35 %) of glucose via enzymatic saccharification. In addition, multiple enrichment cycle strategy (MECS) was performed to facilitate the recyclability of the HADES. The results showed that the enriched lignin recovered by MECS was activated by in-situ demethoxylation reaction. And such lignin fraction could be easily assembled into homogeneous lignin nanoparticles (LNPs, ∼31.51 nm in diameter) by simple sonication. Meanwhile, the MECS signally energized the antioxidant activity of the enriched lignin. Based on the high-efficiency cascade fractionation with the coupled CHTP-HADES fractionation strategy, it will observably boost the effectiveness and scalability of the advanced biorefinery strategy.

Production of xylose polysaccharides using newly isolated Chlamydomonas sp. Xylok with nitrogen depletion

The growing interest in sustainable production of polysaccharides derived from microalgae has stimulated our pursuit of a novel biorefinery approach capable of simultaneously generating exopolysaccharide (EPS) and biomass using a new microalgal strain. In the present study, a novel strain, designated as Chlamydomonas sp. Xylok, was successfully isolated from river water contaminated with copper and zinc. This unique strain exhibited remarkable attributes, demonstrating both a high EPS generation capacity and exceptional biomass production compared to previously documented microalgal types. To optimize EPS produced from Chlamydomonas sp. Xylok, a comprehensive investigation of influential parameters, including light intensity, temperature, and crucial nutrient elements, such as nitrogen, phosphorus, calcium, and magnesium, was conducted. Notably, under nitrogen-depleted conditions, the strain exhibited a rapid and remarkable 49 % increase in EPS production within a mere 24-h timeframe compared to normal growth conditions. In addition to its EPS production potential, Chlamydomonas sp. Xylok holds industrial importance owing to its higher yield of xylose compared to other existing microalgal strains. This unique characteristic presents a cost-effective and efficient method for producing xylose, making it more appealing for various commercial applications.

Upgrading dry acid pretreatment by post-hydrolysis for carbon efficient conversion of lignocellulose

Dry acid pretreatment (DAP) as a promising process for industrial biorefinery provide an efficient bioconversion of cellulose without free wastewater, although the partial xylan and lignin degrade to inhibitors or recondense. A biorefinery strategy for carbon efficient conversion of lignocellulose into bioethanol, xylose, and reactive lignin was developed by upgrading DAP with post-hydrolysis. The results showed that lignocellulose after mild DAP (175 °C, acid dosage of 15 mg/g dry material) obtained higher xylan recovery and lower inhibitors than that of general DAP. Subsequently, post-hydrolysis, simultaneous saccharification and ethanol fermentation were performed at solids loading of 20 wt% without detoxification and sterilization, resulting in xylose and ethanol yield of 71.8 % and 67.6 %. The fractionated lignin presented more reactive β-aryl ether linkages and less condensation than that from DAP. 66 % of lignocellulose carbon was recovered as ethanol, xylose and reactive lignin. This upgrading biorefinery strategy provided an easy-to-operate process for integrated utilization of lignocellulose.

Surfactant-assisted dilute ethylenediamine fractionation of corn stover for technical lignin valorization and biobutanol production

In this study, a surfactant-assisted diluted ethylenediamine (EDA) fractionation process was investigated for co-generation of technical lignin and biobutanol from corn stover. The results showed that the addition of PEG 8000 significantly enhanced cellulose recovery (88.9 %) and lignin removal (68.9 %) in the solid fraction. Moreover, the pulp achieved 86.5 % glucose yield and 82.6 % xylose yield in enzymatic hydrolysis. Structural characterization confirmed that the fractionation process promoted the preservation of active β-O-4 bonds (35.8/100R) in isolated lignin and functionalized the lignin through structural modification using EDA and surfactant grafting. The enzymatic hydrolysate of the pulps yielded a sugar solution for acetone-butanol-ethanol (ABE) fermentation, resulting in an ABE concentration of 15.4 g/L and an overall yield of 137.2 g/Kg of dried corn stalk. Thus, the surfactant-assisted diluted EDA fractionation has the potential to enhance the overall economic feasibility of second-generation biofuels production within the framework of biorefinery.

Optimization of potassium hydroxide combined urea pretreatment and enzymatic hydrolysis of wheat straw using response surface methodology for improving sugar production

To improve sugar yields from wheat straw (WS), response surface methodology (RSM) was adopted to optimize potassium hydroxide combined urea pretreatment and enzymatic hydrolysis of WS. Glucose and xylose yields from the pretreated WS were used as responses during the whole optimization. Potassium hydroxide concentration, time and temperature during pretreatment were found to have significant effects on sugar yields. Sugar yields could be enhanced while WS was pretreated using 45 g/L potassium hydroxide solution containing 15 g/L urea with solid to liquid ratio of 1:5 (g/mL) at 74.0 °C for 50 min. Cellulose recovery, hemicellulose recovery, and lignin removal after optimization were 98.1%, 72.6%, and 75.8%, respectively. In addition, enzyme loading, biomass loading, and reaction time during enzymatic hydrolysis also had significant effects on sugar yields. Maximal yields of glucose (610.25 mg/gds, miligram per gram dry substrate) and xylose (221.26 mg/gds) could be achieved while hydrolysis was carried out at 50 °C for 32.8 h with 141 g/L of biomass loading, 8.1 FPU/gds (filter paper activity unit per gram dry substrate) of enzyme loading and 0.4% (w/v) of polysorbate 80. The corresponding cellulose conversion and hemicellulose conversion were 97.2% and 90.4%, respectively.

Enhancement of Liquid Hot Water Pretreatment on Corn Stover with Ball Milling to Improve Total Sugar Yields

Conversion of the lignocellulosic biomass to bioethanol contributes to the reduction of greenhouse gas emissions, enhancement of energy security, utilization of waste materials, and the promotion of sustainable agricultural practices. In this study, we report the effect of combining ball milling followed by liquid hot water (LHW) pretreatment of corn stover to lower the amount of enzyme required while also greatly increasing the recovery of xylose in fermentable form compared to either pretreatment alone. Short-duration ball milling for 60 min reduces the particle size of corn stover to 37.3 μm; however, the glucose only increased to 47% compared to 32% for unpretreated corn stover. In contrast, liquid hot water pretreatment alone can achieve increasing enzyme hydrolysis yields of cellulose from 49% to 93% as the pretreatment severity factor is increased from 3.24 to 4.41. However, the xylose yield decreased to 36% due to the fact that a considerable part of the xylose was degraded into furfural and humins. Surprisingly, the combination of mild ball milling (30 min) followed by mild liquid hot water pretreatment (190 °C, 15 min) could achieve both high glucose (83%) and xylose (72%) yields for a total sugar yield of 79%, theoretically. Thus, combining ball milling with liquid hot water pretreatment allows for milder conditions for both processes that lead to enhanced cellulose conversion without sacrificing xylose to degradation, which hinders enzymatic hydrolysis.

Enhancement of lignin removal from poplar prehydrolysis liquor by manganese peroxidase-induced polymerization

The removal of lignin from prehydrolysis liquor (PHL) is important for the effective use of saccharides. Manganese peroxidase (MnP) was used for treating PHL to separate the lignin through the use of activated carbon (AC). The effects of MnP on lignin removal were monitored and the reaction mechanism was investigated. It was found that MnP converted the phenolic hydroxyl groups of lignin into phenoxy radicals, leading to lignin polymerization by coupling with β-O-4, β-β, and β-5 bond types, thus enhancing lignin adsorption by AC within the PHL. The combination of MnP and AC treatment led to the 65.71 % removal of lignin, with an increase of 70.68 % compared to the AC-treated PHL. The saccharide contents were largely unaffected by MnP, while the total xylose yield was 97.76 %. Furthermore, the total high heating value of AC after adsorption was 71.12 MJ·kg−1.

Designing of recombinant hydrolytic enzymes cocktail for effective saccharification of delignified rice straw

Enzymatic saccharification is the most crucial and challenging step in lignocellulosic biorefineries for bioethanol production. The enzymatic saccharification requires a cocktail of hydrolytic enzymes, cellulases and hemicellulases for effective degradation of biomass. However, the complete bioconversion of biomass is governed by the proportion and synergistic action of hydrolytic enzymes present in the cocktail. Thus, this study aims to formulate an enzyme cocktail consisting of recombinant cellulases (bifunctional cellulolytic chimeric enzyme, CtGH1-L1-CtGH5-F194A and cellobiohydrolase, CtCBH5A) and xylanases (endo-1,4-β-xylanase, CtGH11A, and β-xylosidase, BoGH43), all in crude form (unpurified enzyme present in the total cellular proteins) for producing high yield of total reducing sugars using choline chloride:acetic acid pretreated rice-straw (CApRS). D-optimal mixture design approach was used for statistically designing the optimal proportion of crude recombinant enzyme cocktail for hydrolysis of delignified rice straw. The developed enzyme cocktail comprising chimera, CtCBH5A, CtGH11 and BoGH43 in ratio 35.1:41.8:10.0:13.1 resulted in cellulolytic enzyme activity, 5.6 FPU/mL and xylanase activity, 102 U/mL. Enzymatic saccharification of 3% (w/v) delignified CApRS using developed enzyme cocktail at 187 FPU/gCApRS, pH 5.8 and 35 °C, yielded total reducing sugar of 498 mg/gbiomass, glucose yield (410 mg/g) and xylose yield (71.3 mg/g) resulting in 72% saccharification efficiency. Whereas, significantly low total reducing sugar yield of 80 mg/g and 218 mg/g were released from raw RS and partially pretreated RS, respectively, by the developed cocktail under the same hydrolytic conditions, thereby inferring the effectiveness of the enzyme cocktail against CApRS biomass. The developed enzyme cocktail was compared with a commercial enzyme cocktail and prospects its applicability in lignocellulosic biorefineries.