Xylose Production Research Articles

Effect of LHW, HCl, and NaOH pretreatment on enzymatic hydrolysis of sugarcane bagasse: sugar recovery and fractal-like kinetics

Conversion of lignocellulose to sugars involves two main processes, namely pretreatment and enzymatic hydrolysis. Lignocellulose pretreatment leads to the degradation of enzymatic recalcitrance of substrate for achieving efficient saccharification. In this study, liquid hot water (LHW), hydrochloric acid (HCl), and sodium hydroxide (NaOH) were as reagents used to pretreat sugarcane bagasse (SB). Results showed that LHW, HCl, and NaOH pretreatment could solubilize 95.3%, 94.7% xylan and 88.7% lignin, respectively. Enzymatic hydrolysis of pretreated SB showed that the maximum glucose (26.0 g/L) and xylose (12.7 g/L) concentration were produced by NaOH pretreatment, and slightly more glucose and less xylose were produced after HCl pretreatment compared to LHW pretreatment. Addition of Tween 80 or xylanase could significantly improve both glucose and xylose production. At 48 h, the glucose increase for LHW, HC1 and NaOH pretreatment was 38.3%, 26.4% and 8.0%, respectively, and the xylose increase for them was 35.0%, 24.9% and 1.7%, respectively. Fractal-like kinetics showed that the value of rate constant increased after the addition of Tween 80 or xylanase, and the efficiency of enzymatic hydrolysis mainly depended on rate constant other than fractal dimension of substrate. Totally, substrate accessibility was dominated for efficient of lignocellulose to sugar compared to enzyme loading. The application of fractal-like theory on the heterogeneous enzymatic hydrolysis of lignocellulose was quite successful.

The Potential of Using Immobilized Xylanases to Enhance the Hydrolysis of Soluble, Biomass Derived Xylooligomers.

Earlier work had indicated that enzyme-mediated hydrolysis of xylooligomer-rich water-soluble streams (derived from steam pre-treated wheat straw) resulted in the effective production of xylose which was subsequently used to produce bio-glycol. In the work reported here, both the thermostability and recyclability of xylanases were significantly improved by covalent immobilizing the enzymes onto alginate beads. The immobilized xylanases showed a lower hydrolytic potential (~55% xylooligomer conversion) compared to the commercial xylanase cocktail HTec3 (~90% xylooligomer conversion) when used at the same protein loading concentration. This was likely due to the less efficient immobilization of key higher molecular weight enzymes (>75 kDa), such as β-xylosidases. However, enzyme immobilization could be improved by lowering the glutaraldehyde loading used to activate the alginate beads, resulting in improved hydrolysis efficacy (~65% xylooligomer conversion). Enzyme immobilization improved enzyme thermostability (endoxylanase and β-xylosidase activities were improved by 80% and 40%, respectively, after 24 h hydrolysis) and this allowed the immobilized enzymes to be reused/recycled for multiple rounds of hydrolysis (up to five times) without any significant reduction in their hydrolytic potential.

Evaluating the production of monosaccharides and xylooligosaccharides from the pre-hydrolysis liquor of kraft pulping process by acid and enzymatic hydrolysis

Pre-hydrolysis liquor (PHL) from the kraft-based dissolving pulp process contains large amounts of hemicelluloses and their degradation products, which makes it a promising candidate for the production of xylose or xylooligosaccharides (XOS). However, it is usually treated as wastewater of the pulp and paper industries. In this study, both acid hydrolysis and enzymatic hydrolysis were applied to prepare xylose and XOS from the PHL, which contained 47.80 g/L of sugars and 14.10 g/L of lignins. Results showed that an optimal xylose yield (30.10 g/L) was obtained at 120 °C for 0.5 h with 4% aqueous sulfuric acid, while the maximum XOS yield (11.63 g/L) was achieved with 0.3% aqueous sulfuric acid at 120 °C for 2.0 h. For the enzymatic hydrolysis, the highest XOS yield of 15.65 g/L was obtained under the optimal condition (60 IU/L PHL, 50 °C, 6 h), and the XOS were mainly composed of xylobiose and xylotriose.

Sequential Production of Xylose, Levulinic Acid and Activated Carbon from Pine Wood

AbstractIn this work, a sequential production of bioenergy platform intermediates (i. e., xylose and levulinic acid (LA)) and carbon materials from pine wood was developed by a three‐step conversion technology. Firstly, the hemicellulose in pine wood was hydrolyzed, obtaining 12.8 wt% xylose and 68.9 wt% solid products containing cellulose and lignin. Secondly, the solid products were hydrolyzed, obtaining 30.6 wt% LA and 42.0 wt% solid residues containing humins and lignin. Thirdly, the solid residues were used for activated carbon (AC) production through potassium hydrate (KOH) activation followed by pyrolysis from 400–800 oC. An AC obtained at a pyrolysis temperature of 800 oC had a high Brunauer‐Emmett‐Teller (BET) surface area of 2436 m2/g and pore volume of 0.91 cm3/g, which exhibited an excellent reactive brilliant red X‐3B (RBRX‐3B) adsorption capacity of 892 mg/g. As a case, 1000 g of pine wood finally produced 128 g xylose, 211 g LA and 39 g high‐performance activated carbon.

Effect of disulfide bridge on hydrolytic characteristics of xylanase from Penicillium janthinellum

Highly efficient and stable enzymes are required for application in biotechnology, to meet the technical, environmental, and economic industrial demands. Xylanases are hemicellulolytic enzymes that degrade the heteroxylan constituent of the lignocellulosic plant cell wall. In this study, an acidic xylanase designated Pjxyn (pH 4.0) from Penicillium janthinellum was engineered by the introduction of a disulfide bridge. This strategy exploited the influence of the bridge on hydrolysis characteristics and enhanced hydrolysis was achieved. Three mutants [PjxynS(27)S(39), PjxynS(27)S(186), and PjxynS(39)S(186)] produced more xylose and xylobiose as hydrolysis products compared with the wild-type Pjxyn, when commercial xylans and lab-prepared water-insoluble corncob-xylan were used as the substrates, especial for the PjxynS(27)S(39) mutant, the content of xylose and xylobiose was 87.62% (using beechwood xylan) and 69.91% (using oat-spelt xylan) higher than that in the hydrolysis products of Pjxyn. Moreover, each mutant combined with the xylanase mutant T-XynFM effectively decreased the production of xylose with an optimum xylobiose yield. The findings demonstrate the potential industrial value of engineering xylanase to improve its hydrolytic properties and thermostability.

Production of ethylene glycol from xylose by metabolically engineered Escherichia coli

Ethylene glycol (EG) is an important chemical used for several industrial applications including poly(ethylene terephthalate) synthesis. In this study, Escherichia coli was metabolically engineered to efficiently produce EG from xylose. To biosynthesize EG, the Dahms pathway was introduced by expressing xylBC genes from Caulobacter crescentus (xylBCccs). Various E. coli strains and glycolaldehyde reductases were screened to find E. coli W3110 strain and glycolaldehyde reductase (yqhD) as optimal combination for EG production. In silico genome‐scale metabolic simulation suggested that increasing the native xylose pathway flux, in the presence of the overexpressed Dahms pathway, is beneficial for EG production. This was achieved by reducing the Dahms pathway flux by employing a synthetic small regulatory RNA targeting xylBccs. Fed‐batch culture of the final engineered E. coli strain produced 108.2 g/L of EG in a xylose minimal medium. The yield on xylose and EG productivity were 0.36 g/g (0.87 mol/mol) and 2.25 g/L/h, respectively. © 2018 American Institute of Chemical Engineers AIChE J, 64: 4193–4200, 2018

Isolation of Low-Abundant Bacteroidales in the Human Intestine and the Analysis of Their Differential Utilization Based on Plant-Derived Polysaccharides.

Bacteroidales are the most abundant Gram-negative bacteria flourished in the human intestine with great underlying benefits to be discovered and developed as the next-generation probiotics. However, the traditional isolation method limits the mining of low-abundant species. In this study, modified selective medium was established using xylan as the sole carbohydrate source to enrich low-abundant species such as Prevotella copri and Bacteroides xylanisolvens from healthy human fecal samples. The growth rate, transcriptomics, and metabolomics profiles of the enriched low-abundant species were then evaluated. The considerable upregulated genes encoding xylan-associated hydrolysis and transportation, along with the increased xylose production detected in the culture of the enriched Bacteroidales strains based on xylan, were considered as positive proof of the feasibility of the modified methodology.

Process Optimization of Steam Explosion Parameters on Multiple Lignocellulosic Biomass Using Taguchi Method—A Critical Appraisal

Xylitol is a low calorie sweetener that can be produced through a bioconversion approach from lignocellulosic biomass that requires pretreatment prior to the bioconversion of xylose to xylitol. Steam explosion (SE) is an industrially scalable pretreatment (PT) process with the potential to liberate xylose monomers, however SE-PT has not been optimised for xylose release from multiple feedstock. The effect of pressure, substrate weight, phosphoric acid loading concentration and residence time on four feedstock (wheat straw (WS), corn stover (CS), Miscanthus (M), and willow (W)) for xylose release and minimal fermentation inhibitor productions (furfural and 5-hydroxymethylfurfural (HMF)) was investigated using the Taguchi methodology for design of experiment (DoE) with variation at four levels (44). An L16 orthogonal array design was utilised and all factors indicated influence on xylose release and inhibitor formation and the resulting xylose rich hydrolysate assessed for bioconversion to xylitol.. The L16 DoE gave hydrolysates containing 75-95% of xylose content in the original biomass, whilst retaining cellulose and lignin components in the fibre. The level of inhibitors were within boundary limits to enable microbial fermentation of the hydrolysates to xylitol. Fine tuning of the overall evaluation criteria (OEC) model imbibing 1.5 kg feedstock in 1.2% w/v orthophosphoric acid, 12 bar(g) and 6 minutes residence time resulted in 90% xylose recovery and production of >1000 L of wheat straw hydrolysate for bioconversion to xylitol. The advantages and limitations of the Taguchi OEC model and further improvements to this process are discussed in a biorefining context

Subcritical Water-Carbon Dioxide Pretreatment of Oil Palm Mesocarp Fiber for Xylooligosaccharide and Glucose Production.

The present work aimed to investigate the pretreatment of oil palm mesocarp fiber (OPMF) in subcritical H2O-CO2 at a temperature range from 150–200 °C and 20–180 min with CO2 pressure from 3–5 MPa. The pretreated solids and liquids from this process were separated by filtration and characterized. Xylooligosaccharides (XOs), sugar monomers, acids, furans and phenols in the pretreated liquids were analyzed by using HPLC. XOs with a degree of polymerization X2–X4 comprising xylobiose, xylotriose, xylotetraose were analyzed by using HPAEC-PAD. Enzymatic hydrolysis was performed on cellulose-rich pretreated solids to observe xylose and glucose production. An optimal condition for XOs production was achieved at 180 °C, 60 min, 3 MPa and the highest XOs obtained was 81.60 mg/g which corresponded to 36.59% of XOs yield from total xylan of OPMF. The highest xylose and glucose yields obtained from pretreated solids were 29.96% and 84.65%, respectively at cellulase loading of 10 FPU/g-substrate.

Sugarcane bagasse as a novel carbon source for heterotrophic cultivation of oleaginous microalga Schizochytrium sp.

Oleaginous microalgae are known as promising oil producers, which accumulate high amount of lipids from various carbon substrates. This study first investigated sugarcane bagasse hydrolysate as a cheap carbon source for the production of biomass and lipid by Schizochytrium sp. The sugarcane bagasse was pretreated with alkali followed by phosphoric acid to remove lignin and enhance xylose production, respectively. The enzymatic hydrolysis of the pretreated sugarcane bagasse by cellulase was subsequently optimized. A maximum glucose yield of 95.77% was obtained at an enzyme loading of 0.3 mL/g with a hydrolysis reaction time of 48 h. The sugarcane bagasse hydrolysate containing glucose and xylose was subsequently used as a substrate for cultivating Schizochytrium sp. Results showed that sugarcane bagasse hydrolysate performed better than refined glucose for cell growth and lipid accumulation. The maximum biomass (10.45 g/L) and lipid content (45.15%) were achieved by growing Schizochytrium sp. in a medium containing 40 g/L glucose in sugarcane bagasse hydrolysate for 72 h. Sugarcane bagasse hydrolysate also resulted in higher levels of polyunsaturated fatty acid and docosahexaenoic acid than did refined glucose. This study suggests that sugarcane bagasse hydrolysate is a low-cost and effective carbon source for microalgal biomass and lipid production.

Xylose Production By Combined Autohydrolysis and Enzymatic Hydrolysis From Tobacco Stalks

Tütün sapları, yaprakları alındıktan sonra geride kalan ksilanca zengin, önemli bir ekonomik değeri bulunmayan ancak ksiloz ve ksilitol üretimi için potansiyel bir kaynak oluşturacak bir atıktır. Ksiloz genellikle kimyasal metotlarla üretilir;  bu yöntemle asit gibi korozif kimyasalların kullanılması ya da işlem sırasında istenmeyen bileşiklerin oluşması gibi olumsuzluklar görülmektedir. Alternatif olarak, ksiloz enzim hidroliziyle de üretilebilir. Enzimatik hidroliz daha spesifik olduğu gibi, reaksiyon ılımlı koşullarda gerçekleşir ve hidroliz aşamasında istenmeyen bileşikler oluşmaz. Bu çalışmada tütün sapları 160°C’de 1 saatte ekstrakte edilen ksilanca zengin likörden Trichoderma longibrachiatum ksilanazı ile ksiloz üretilmiştir. Hidrolizasyon işlemi cevap yüzey yöntemi ile optimize edilmiştir. Optimum substrat ve enzim konsantrasyonu 0.28 g atık/mL KOL ve 228 U/mL olarak bulunmuştur. Optimum koşullar altında yapılan hidrolizasyonunda ise ksiloz %79.8 verimle ve 1.9 g/g seçicilikle üretilmiştir.

Microwave-Assisted Oxalic Acid Pretreatment for the Enhancing of Enzyme Hydrolysis in the Production of Xylose and Arabinose from Bagasse.

In this study, highly-efficient hydrolysis of bagasse into xylose and arabinose sugars (C5 sugars) was developed by microwave-assisted oxalic acid pretreatment under mild reaction conditions. The effects of acid and hydrolysis conditions on the C5 sugar yields were discussed. The results showed that oxalic acid performed better than hydrochloric acid and maleic acid, and was a promising alternative to sulfuric acid for xylose production at the same acid concentration. The maximum yields of xylose (95.7%) and arabinose (91.5%) were achieved via the microwave-assisted oxalic acid pretreatment (120 °C, 10 min, 0.4 mol/L, solid–liquid ratio of 1:50 g/mL), indicating that almost all xylan-type hemicelluloses were released from the cell wall and hydrolyzed into C5 sugars. After pretreatment, more than 90% of the cellulose in the residual bagasse was converted to glucose (92.2%) by enzymatic hydrolysis. This approach could realize the highly-efficient hydrolysis of xylan from bagasse into C5 sugars, which would enhance the enzyme hydrolysis of treated bagasse into glucose.

Production of ethanol and xylitol by Trametes membranacea.

The potential to produce ethanol and xylitol from xylose by the macro basidiomycete Trametes membranacea was evaluated. All strains studied showed ethanol and xylitol production. The highest ethanol production of xylose was obtained by T. membranacea strain TM158/10 with 5.65 ± 0.21g/L at pH 4 and 28°C with 288h of fermentation and 5.59 ± 0.05g/L ethanol concentration at pH 5 and 24°C with 360h of fermentation. When the conversion was carried out using sugars generated from enzymatic hydrolysis of sugarcane bagasse, there were higher yields from 74 to 15% for ethanol and xylitol, respectively. Although the ethanol and xylitol production need to be optimized, this study showed for the first time the possibility of using T. membranacea for the simultaneous xylitol and ethanol production from pentose sugars, allowing for the possibility of using all released sugars during the hydrolysis of lignocelluloses.

Integrated approach for extraction of xylose, cellulose, lignin and silica from rice straw

In this paper, a novel process for xylose production was developed and discovered with simultaneous extraction of other product like cellulose, silica, and lignin. The study explored the effect of chemicals on xylose yield, and the xylose production process was optimized as followings: After pre-impregnation with nitric acid at 140°C for 15min, rice straw was treated at 1bar with 0.5% (v/v) nitric acid, followed by second hydrolysis by using 2.5%(w/v) sodium hydroxide with 2%(w/v) sodium hypochlorite at 121°C for 1h, decoloration and ionic impurities were removed by ion exchange. Using this process, 13.8g of crystal xylose was produced from 100g rice straw, simultaneously 26.01% (w/w) of cellulose, 10.11% (w/w) silica, and 6.21% (w/w) lignin were also extracted from rice straw respectively. All results indicated that this process is a more effective than the traditional method sulphuric acid hydrolysis process for lignocellulose biorefinery.

Carbon-Based Solid Acid Pretreatment in Corncob Saccharification: Specific Xylose Production and Efficient Enzymatic Hydrolysis

In this paper, we disclose a novel saccharification technology for lignocellulosic biomass. A new carbon-based solid (C-SO3H) acid catalyst was first synthesized by a simple, one-step hydrothermal ...

Optimizing xylose production from pinewood sawdust through dilute-phosphoric-acid hydrolysis by response surface methodology

Abstract Response surface methodology was used to optimize the xylose production from pinewood sawdust through dilute-phosphoric-acid hydrolysis. The effects of independent variables on xylose yield were investigated, including reaction temperature (75–175 °C), reaction time (0–7.2 h), solution-to-feed ratio (4–20 mL/g), and phosphoric-acid concentration (0–6.67 wt%). Results indicated that the individual factor H3PO4 concentration and the interacting factors including temperature × time, temperature × H3PO4 concentration, and solution-to-feed ratio × H3PO4 concentration were all significant factors. Long reaction time (>5.4 h) and high phosphoric-acid concentration (>5%) showed little effect. Xylose yield increased with increasing temperature up to 125 °C. Higher phosphoric-acid concentration and larger solution-to-feed ratio also increased xylose yield. The coefficient of determination, corresponding analysis of variance, and parity plot indicated that the fitted model was appropriate for the acid-hydrolysis process. The maximum xylose production of 90.95% could be obtained with the reaction temperature of 106.7 °C, reaction time of 4.57 h, phosphoric-acid concentration 4.49 wt%, and solution-to-feed ratio of 12.51 mL/g.

Furfural production from biomass pretreatment hydrolysate using vapor-releasing reactor system

Biomass hydrolysate from autohydrolysis pretreatment was used for furfural production considering it is in rich of xylose, xylo-oligomers, and other decomposition products from hemicellulose structure. By using the vapor-releasing reactor system, furfural was protected from degradation by separating it from the reaction media. The maximum furfural yield of 73% was achieved at 200 °C for biomass hydrolysate without the use of the catalyst. This is because the presence of organic acids such as acetic acid in hydrolysate functioned as a catalyst. According to the results in this study, biomass hydrolysate with a vapor-releasing system proves to be efficient for furfural production. The biorefinery process which allows the separation of xylose-rich autohydrolysate from other parts from biomass feedstock also improves the overall application of the biomass.

Production of Xylitol from Agricultural Waste by Enzymatic Methods

Enzyme catalyzed production of xylose from autoclaved and non-autoclaved wheat straw was conducted followed by bioconversion of xylose to xylitol using a Crude preparation of Xylose Reductase (CXR) from Candida guillermondii. Ground wheat straw (autoclaved and non autoclaved) was treated at 40 and 50°C for up to 9 h at pH 4.5 with various concentrations of xylanase (12.4 to 37.2 U) and the reactions were assayed for reducing sugars. Hydrolysis of autoclaved wheat straw at 50°C for 3 h with 24.8 U of xylanase at pH 4.5 resulted in the highest yield of xylose (9.8% of total xylose). Overall, the autoclave pre-treatment resulted in a 22% higher yield of reducing sugars compared to the non pre-treated samples. The xylose hydrolysed wheat straw was adjusted to pH 7 and the effects of temperature, pH, time and CXR concentration were investigated to determine optimum conditions for xylitol production with NADPH. The optimal conditions for the synthesis of xylitol were 30°C at pH 7 for 8 h with 7.92 U of CXR and 10 mM NADPH with 23.9 g xylose. This research shows that xylitol synthesis using only an enzymatic system is feasible.

Improvement in xylooligosaccharides production by knockout of the β-xyl1 gene in Trichoderma orientalis EU7-22.

The goal of this study was to enhance the production of xylooligosaccharides (XOs) and reduce the production of xylose. We investigated β-xylosidases, which were key enzymes in the hydrolysis of xylan into xylose, in Trichoderma orientalis EU7-22. The binary vector pUR5750G/bxl::hph was constructed to knock out the β-xyl1 gene (encoding β-xylosidases) in T. orientalis EU7-22 by homologous integration, producing the mutant strain T. orientalis Bxyl-1. Xylanase activity for strain Bxyl-1 was 452.42IU/mL, which increased by only 0.07% compared to that of parental strain EU7-22, whereas β-xylosidase activity was 0.06IU/mL, representing a 91.89% decrease. When xylanase (200IU/g xylan), produced by T. orientalis EU7-22 and T. orientalis Bxyl-1, was used to hydrolyze beechwood xylan, in contrast to the parental strain, the XOs were enhanced by 83.27%, whereas xylose decreased by 45.80% after 36h in T. orientalis Bxyl-1. Based on these results, T. orientalis Bxyl-1 has great potential for application in the production of XOs from lignocellulosic biomass.

Sequential and simultaneous strategies for biorefining of wheat straw using room temperature ionic liquids, xylanases and cellulases

Sequential and simultaneous strategies for fractioning wheat straw were developed in combining 1-ethyl-3-methyl imidazolium acetate [C2mim][OAc], endo-xylanases from Thermobacillus xylanilyticus and commercial cellulases. After [C2mim][OAc]-pretreatment, hydrolysis catalyzed by endo-xylanases of wheat straw led to efficient xylose production with very competitive yield (97.6 ± 1.3%). Subsequent enzymatic saccharification allowed achieving a total degradation of cellulosic fraction (>99%). These high performances revealed an interesting complementarity of [C2mim][OAc]- and xylanase-pretreatments for increasing enzymatic digestibility of cellulosic fraction in agreement with the structural and morphological changes of wheat straw induced by each of these pretreatment steps. In addition a higher tolerance of endo-xylanases from T. xylaniliticus to [C2mim][AcO] until 30% v/v than cellulases from T. reesei was observed. Based on this property, a simultaneous strategy combining [C2mim][OAc]- and endo-xylanases as pretreatment in a one-batch produced xylose with similar yield than those obtained by the sequential strategy.