Xylose Recovery Research Articles

The effect of Pleurotus ostreatus arabinofuranosidase and its evolved variant in lignocellulosic biomasses conversion

The fungal arabinofuranosidase from Pleurotus ostreatus PoAbf recombinantly expressed in Pichia pastoris rPoAbf and its evolved variant rPoAbf F435Y/Y446F were tested for their effectiveness to enhance the enzymatic saccharification of three lignocellulosic biomasses, namely Arundo donax, corn cobs and brewer’s spent grains (BSG), after chemical or chemical–physical pretreatment. All the raw materials were subjected to an alkaline pretreatment by soaking in aqueous ammonia solution whilst the biomass from A. donax was also pretreated by steam explosion. The capability of the wild-type and mutant rPoAbf to increase the fermentable sugars recovery was assessed by using these enzymes in combination with different (hemi)cellulolytic activities. These enzymatic mixtures were either entirely of commercial origin or contained the cellulase from Streptomyces sp. G12 CelStrep recombinantly expressed in Escherichia coli in substitution to the commercial counterparts. The addition of the arabinofuranosidases from P. ostreatus improved the hydrolytic efficiency of the commercial enzymatic cocktails on all the pretreated biomasses. The best results were obtained using the rPoAbf evolved variant and are represented by increases of the xylose recovery up to 56.4%. These data clearly highlight the important role of the accessory hemicellulolytic activities to optimize the xylan bioconversion yields.

Combined pretreatment using alkaline hydrothermal and ball milling to enhance enzymatic hydrolysis of oil palm mesocarp fiber

Hydrothermal pretreatment of oil palm mesocarp fiber was conducted in tube reactor at treatment severity ranges of log Ro=3.66–4.83 and partial removal of hemicellulose with migration of lignin was obtained. Concerning maximal recovery of glucose and xylose, 1.5% NaOH was impregnated in the system and subsequent ball milling treatment was employed to improve the conversion yield. The effects of combined hydrothermal and ball milling pretreatments were evaluated by chemical composition changes by using FT-IR, WAXD and morphological alterations by SEM. The successful of pretreatments were assessed by the degree of enzymatic digestibility of treated samples. The highest xylose and glucose yields obtained were 63.2% and 97.3% respectively at cellulase loadings of 10FPU/g-substrate which is the highest conversion from OPMF ever reported.

Acetone–butanol–ethanol (ABE) production by Clostridium beijerinckii from wheat straw hydrolysates: Efficient use of penta and hexa carbohydrates

ABE fermentation by Clostridium beijerinckii of steam-exploded and ozonated wheat straw hydrolysates was investigated. In steam-exploded hydrolysates, highest yields of 0.40g/g ABE yield and 127.71gABE/kg wheat straw were achieved when the whole slurry from the pretreatment was used. In ozonated hydrolysates, 0.32g/g ABE yield and 79.65gABE/kg wheat straw were obtained from washed ozonated wheat straw. Diverse effects were observed in steam explosion and ozonolysis of wheat straw which resulted in hemicellulose removal and acid insoluble lignin solubilization, respectively. SEM analysis showed structural differences in untreated and pretreated biomass. Depending on the operational strategy, after pretreatment and enzymatic hydrolysis, the glucose recovery ranged between 65.73–66.49% and 63.22–65.23% and the xylose recovery ranged between 45.19–61.00% and 34.54–40.91% in steam-exploded and ozonated hydrolysates, respectively. The effect of the main inhibitory compounds found in hydrolysates (oxalic acid, acetic acid, 5-hydroxymethylfurfural and furfural) was studied through ABE fermentation in model media.

Effects of Harvest and Storage of Switchgrass on the Recovery of Carbohydrates during Dilute Acid Pretreatment and Enzymatic Hydrolysis

Perennial forage grasses have potential as cellulosic feedstocks. Outside storage as round bales is a likely mode of storage; however, little is known of storage effects. The objective of this study was to determine the effects of baled storage method on saccharification, namely the recovery of glucose and xylose, and production of inhibitors after dilute acid pretreatment and enzymatic hydrolysis. Mature switchgrass (Panicum virgatum L. cv. Alamo) was harvested in Fayetteville, AR and packaged in large round bales in October 2010. There were two baling times: one soon after cutting when there was no rainfall and the other after a rainfall event. The bales that did not receive rain were stored either in an open barn or unprotected in the field. Bales made from rained-on switchgrass were only stored unprotected in the field. Samples were taken from the windrows right before baling, and after a maximum 65-day storage period. Field storage increased lignin content in biomass relative to barn storage, but carbohydrate constituents were not affected. Field storage decreased production of hydroxymethylfurfural and increased production of furfural relative to barn storage. Results indicate that protected storage conditions for switchgrass biomass in round bales can lead to greater preservation of fermentable sugars and reduced production of the important inhibitor furfural.

Wet explosion pretreatment of sugarcane bagasse for enhanced enzymatic hydrolysis

Wet explosion pretreatment of sugarcane bagasse was investigated in pilot-scale with the aim of obtaining the highest possible sugar yield after pretreatment. The temperatures used were 155, 170, 185 and 200 °C with or without addition of oxygen (0.6 MPa pressure). Enzymatic hydrolysis of washed solid cakes was carried out using two loadings of enzyme mixtures as enzyme protein (EP) on cellulose was 12.4 and 22.0 g kg−1. After hydrolysis, a pretreatment temperature of 185°C with oxygen yielded the highest glucose concentration of 573.9±4.5 g kg−1 TS and a glucose yield of 87.4±0.7% of the theoretical maximum value. Pretreatment at 200°C with oxygen exhibited enhanced enzymatic efficiency but lower xylose recovery and formation of the degradation products such as acetate, furfural and HMF of 7.6, 3.3 and 1.0 g L−1, respectively. In the hydrolysis, the total sugars (glucose+xylose) yielded at 185°C and 200°C with oxygen were 615.9±4.5 and 584.5±3.1 g kg−1 TS, respectively.

Chemical characterization and hydrothermal pretreatment of Salicornia bigelovii straw for enhanced enzymatic hydrolysis and bioethanol potential

Salicornia bigelovii straw was characterized and evaluated as a potential lignocellulosic bioethanol feedstock. S. bigelovii used in the study was grown in the United Arab Emirates using saltwater (40ppt) for irrigation. Salt removal was performed prior to pretreatment to protect the processing equipment and avoid inhibition of enzymes and yeast. Composition of the washed biomass was comparable to traditional lignocellulosic biomasses with relatively high glucan and xylan content (26 and 22g/100gDM, respectively) but with lower lignin content (7g/100gDM). The washed feedstock was subjected to hydrothermal pretreatment, producing highly digestible (up to 92% glucan-to-glucose conversion) and fermentable (up to 100% glucose-to-ethanol conversion) fiber fractions. Liquid fractions obtained in the pretreatment did not show inhibition towards Saccharomyces cerevisiae. No significant differences among the enzymatic convertibility and microbial fermentability of the fibers as well as low xylose recoveries suggest that lower severity pretreatment conditions could be exploited for S. bigelovii.

Enhancing sugar recovery from sugarcane bagasse by kinetic analysis of a two-step dilute acid pretreatment process

Maximising sugar recovery from pretreatment and enzymatic hydrolysis is a determining factor in the economic viability of bio-refineries using lignocellulose as feedstock. Single-step dilute acid treatment of sugarcane bagasse was investigated at times and temperatures ranging between 12 and 22 min and 422–442 K, respectively. Maximum sugar recovery equalled 78% of the mass fraction polysaccharides (recovered as hydrolysis products xylose and glucose) present in sugarcane bagasse. Preferred operating conditions, as determined by response surface methodology (RSM), included an acid (H2SO4) concentration range of 45–55 mmol.L−1, a time of 14.0 min and temperature of 442 K. Complete recovery of both xylose and glucose could not be achieved through the combination of single-step dilute acid treatment and enzymatic hydrolysis. Whereas a short pretreatment time and low pretreatment temperature process was required for maximum xylose recovery, opposing operating conditions had to be applied to maximise glucose recovery. In order to circumvent some of the limitations associated with the single-step process, the use of a two-step process was tested through RSM simulations. A 4.8% increase in the total sugar recovery yield and a 36.1% reduction in furfural production were calculated for the two - in lieu of the one-stage method. The improvement was attributed to the avoidance of xylose degradation reactions but also the production of low enzymatically-digestible solids.

Effect of dilute acid pretreatment on the conversion of barley straw with grains to fermentable sugars

This study investigated the effects of pretreatment conditions, dilute sulfuric acid concentration and treatment time, on the carbohydrate solubility of a mixture of barley straw and grain. The conditions were expressed as combined severity (CS) to evaluate sugar recovery from pretreated samples. Enzymatic hydrolysates from the lignocellulose pretreatment residues were also included to the results. CS was positively correlating with glucose recovery in all conditions, but in higher acid concentrations CS did not predict xylose recovery. It appeared that the residual xylan better indicate the xylose release. An optimal fermentable sugar yield from the mixture of barley straw and grain was obtained by maintaining the CS at around 1.38, corresponding to an overall glucose yield of 96% and a xylose yield of 57%.

Sono-assisted organosolv/H2O2 pretreatment of oil palm (Elaeis guineensis Jacq.) fronds for recovery of fermentable sugars: Optimization and severity evaluation

The evaluation and optimization of sono-assisted organosolv/liquid peroxide pretreatment (SOP) conditions on glucose and xylose recovery from oil palm fronds (OPFs) using severity factors and response surface methodology were investigated for the first time. Pretreatment temperatures (50–80°C) were combined with time (30–70min) to obtain severity factors (0.610⩽R0⩽35.625) and the observation was that after enzymatic saccharification, the yields of fermentable sugars (glucose and xylose) decreased at high severity (R0>8.389). A central composite design (CCD) was used to predict the optimum conditions for the SOP using pretreatment temperature (X1, 50–80°C), pretreatment time (X2, 30–70min), NaOH concentration (X3, 1–2%) and H2O2 concentration (X4, 2–4%) as independent variables. The models had high R2 values (>0.9500) which were able to predict reliable optimum total solids yield (55.59%), glucose concentration in pretreated residue (26.51g/l), xylose concentration in pretreated residue (8.63g/l) and xylose concentration in pretreated liquor (15.15g/l). The optimum responses were attained at 76.82°C (∼75°C), 30.64min (∼30min), 1.39% (∼1.4%) NaOH concentration and 3.42% (∼3.0%) H2O2. SOP is found to be an eco-friendly and efficient method of pretreating OPFs for fermentable substrates for bioethanol production.

Conversion of switchgrass to ethanol using dilute ammonium hydroxide pretreatment: influence of ecotype and harvest maturity

Switchgrass (Panicum virgatum L.) is a perennial C4 grass that is being developed as a bioenergy crop because it has high production yields and suitable agronomic traits. Five switchgrass biomass samples from upland and lowland switchgrass ecotypes harvested at different stages or maturity were used in this study. Switchgrass samples contained 317.0–385.0 g glucans/kg switchgrass dry basis (db) and 579.3–660.2 g total structural carbohydrates/kg switchgrass, db. Carbohydrate contents were greater for the upland ecotype versus lowland ecotype and increased with harvest maturity. Pretreatment of switchgrass with dilute ammonium hydroxide (8% w/w ammonium loading) at 170°C for 20 min was determined to be effective for preparing switchgrass for enzymatic conversion to monosaccharides; glucose recoveries were 66.9–90.5% and xylose recoveries 60.1–84.2% of maximum and decreased with increased maturity at harvest. Subsequently, pretreated switchgrass samples were converted to ethanol by simultaneous saccharification and fermentation using engineered xylose-fermenting Saccharomyces cerevisiae strain YRH400. Ethanol yields were 176.2–202.0 l/Mg of switchgrass (db) and followed a similar trend as observed for enzymatic sugar yields.

Enhanced Xylose Recovery from Oil Palm Empty Fruit Bunch by Efficient Acid Hydrolysis

Oil palm empty fruit bunch (EFB) is abundantly available in Malaysia and it is a potential source of xylose for the production of high-value added products. This study aimed to optimize the hydrolysis of EFB using dilute sulfuric acid (H2SO4) and phosphoric acid (H3PO4) via response surface methodology for maximum xylose recovery. Hydrolysis was carried out in an autoclave. An optimum xylose yield of 91.2 % was obtained at 116 °C using 2.0 % (v/v) H2SO4, a solid/liquid ratio of 1:5 and a hydrolysis time of 20 min. A lower optimum xylose yield of 24.0 % was observed for dilute H3PO4 hydrolysis at 116 °C using 2.4 % (v/v) H3PO4, a solid/liquid ratio of 1:5 and a hydrolysis time of 20 min. The optimized hydrolysis conditions suggested that EFB hydrolysis by H2SO4 resulted in a higher xylose yield at a lower acid concentration as compared to H3PO4.

EFFICIENT PRODUCTION OF BIOETHANOL FROM CORN STOVER BY PRETREATMENT WITH A COMBINATION OF SULFURIC ACID AND SODIUM HYDROXIDE

Corn stover is the most abundant agricultural residue in China and a valuable reservoir for bioethanol production. In this study, we proposed a process for producing bioethanol from corn stover; the pretreatment prior to presaccharification, followed by simultaneous saccharification and fermentation (SSF) by using a flocculating Saccharomyces cerevisiae strain, was optimized. Pretreatment with acid–alkali combination (1% H2SO4, 150°C, 10 min, followed by 1% NaOH, 80°C, 60 min) resulted in efficient lignin removal and excellent recovery of xylose and glucose. A glucose recovery efficiency of 92.3% was obtained by enzymatic saccharification, when the pretreated solid load was 15%. SSF was carried out at 35°C for 36 hr after presaccharification at 50°C for 24 hr, and an ethanol yield of 88.2% was achieved at a solid load of 15% and an enzyme dosage of 15 FPU/g pretreated corn stover.

Pretreatment of Oil Palm Fronds for Improving Hemicelluloses Content for Higher Recovery of Xylose

Lignocelluloses material is known as a potential biomass for conversion into value-added product. Utilization of biomass for beneficial products particularly food and health-related, has gained increasing attention among researchers worldwide and the potential usage of the lignocelluloses biomass is much sought after nowadays. An oil palm frond (OPF) has a great potential to be used as a precursor for production of xylose. In order to increase the yield of xylose, pretreatment of lignocelluloses biomass is important as it will for example, enhance the accessibility of enzyme to convert hemicelluloses xylan into xylose. Therefore in this study, OPF was pre-treated using dilute acid hydrolysis (H2SO4), alkali (NaOH), and autohydrolysis methods. The result showed that autohydrolysis gave higher hemicelluloses content which was 27.80±0.35% as compared to alkali and dilute acid pretreatment with 17.51±0.61% and 27.37±1.89%, respectively. The autohydrolysis pretreated samples were then used for further enzymatic hydrolysis for xylan breakdown into xylose. Recovery of xylose was found to be higher at higher xylanase activity which was16 U. Reaction time of 48 h with 1% substrate was able to produce up to 0.795 g/L xylose.

Two-Stage Acidic–Alkaline Hydrothermal Pretreatment of Lignocellulose for the High Recovery of Cellulose and Hemicellulose Sugars

The focus of this work was to develop a combined acid and alkaline hydrothermal pretreatment of lignocellulose that ensures high recovery of both hexose and pentose. Dilute sulfuric acid and lime pretreatments were employed sequentially. Process performance was optimized in terms of catalyst concentration, retention time, and temperature using response surface methodology. Medium operational conditions in the acid stage and harsh conditions in the alkaline stage were desirable with optimal performance at 0.73wt% H(2)SO(4), 150°C, 6.1min in the first stage, and 0.024g lime/g biomass, 202°C, 30min in the second stage. In comparison to single-stage pretreatments with high recovery of either glucose or xylose, two-stage process showed great promises with >80% glucose and >70% xylose recovery. In addition, the method greatly improved ethanol fermentation with yields up to 0.145g/g Miscanthus, due to significantly reduced formation of inhibitory by-products such as weak acids, furans, and phenols. Supplementing biomimetic acids would further increase glucose yield by up to 15% and xylose yield by 25%.

Ethanol and biogas production after steam pretreatment of corn stover with or without the addition of sulphuric acid

BackgroundLignocellulosic biomass, such as corn stover, is a potential raw material for ethanol production. One step in the process of producing ethanol from lignocellulose is enzymatic hydrolysis, which produces fermentable sugars from carbohydrates present in the corn stover in the form of cellulose and hemicellulose. A pretreatment step is crucial to achieve efficient conversion of lignocellulosic biomass to soluble sugars, and later ethanol. This study has investigated steam pretreatment of corn stover, with and without sulphuric acid as catalyst, and examined the effect of residence time (5–10 min) and temperature (190–210°C) on glucose and xylose recovery. The pretreatment conditions with and without dilute acid that gave the highest glucose yield were then used in subsequent experiments. Materials pretreated at the optimal conditions were subjected to simultaneous saccharification and fermentation (SSF) to produce ethanol, and remaining organic compounds were used to produce biogas by anaerobic digestion (AD).ResultsThe highest glucose yield achieved was 86%, obtained after pretreatment at 210°C for 10 minutes in the absence of catalyst, followed by enzymatic hydrolysis. The highest yield using sulphuric acid, 78%, was achieved using pretreatment at 200°C for 10 minutes. These two pretreatment conditions were investigated using two different process configurations. The highest ethanol and methane yields were obtained from the material pretreated in the presence of sulphuric acid. The slurry in this case was split into a solid fraction and a liquid fraction, where the solid fraction was used to produce ethanol and the liquid fraction to produce biogas. The total energy recovery in this case was 86% of the enthalpy of combustion energy in corn stover.ConclusionsThe highest yield, comprising ethanol, methane and solids, was achieved using pretreatment in the presence of sulphuric acid followed by a process configuration in which the slurry from the pretreatment was divided into a solid fraction and a liquid fraction. The solid fraction was subjected to SSF, while the liquid fraction, together with the filtered residual from SSF, was used in AD. Using sulphuric acid in AD did not inhibit the reaction, which may be due to the low concentration of sulphuric acid used. In contrast, a pretreatment step without sulphuric acid resulted not only in higher concentrations of inhibitors, which affected the ethanol yield, but also in lower methane production.

Constitutive expression of a fungal glucuronoyl esterase in Arabidopsis reveals altered cell wall composition and structure

A family 15 carbohydrate esterase (CE15) from the white-rot basidiomycete, Phanerochaete carnosa (PcGCE), was transformed into Arabidopsis thaliana Col-0 and was expressed from the constitutive cauliflower mosaic virus 35S promoter. Like other CE15 enzymes, PcGCE hydrolyzed methyl-4-O-methyl-d-glucopyranuronate and could target ester linkages that contribute to lignin-carbohydrate complexes that form in plant cell walls. Three independently transformed Arabidopsis lines were evaluated in terms of nine morphometric parameters, total sugar and lignin composition, cell wall anatomy, enzymatic saccharification and xylan extractability. The transgenic lines consistently displayed a leaf-yellowing phenotype, as well as reduced glucose and xylose content by as much as 30% and 35%, respectively. Histological analysis revealed 50% reduction in cell wall thickness in the interfascicular fibres of transgenic plants, and FT-IR microspectroscopy of interfascicular fibre walls indicated reduction in lignin cross-linking in plants overexpressing PcGCE. Notably, these characteristics could be correlated with improved xylose recovery in transgenic plants, up to 15%. The current analysis represents the first example whereby a fungal glucuronoyl esterase is expressed in Arabidopsis and shows that the promotion of glucuronoyl esterase activity in plants can alter the extent of intermolecular cross-linking within plant cell walls.

Corn stover saccharification with concentrated sulfuric acid: Effects of saccharification conditions on sugar recovery and by-product generation

Although concentrated sulfuric acid saccharification is not a novel method for breaking down lignocellulosic biomass, the process by which saccharification affects biomass decomposition, sugar recovery, and by-product generation is not well studied. The present study employed Taguchi experimental design to study the effects of seven parameters on corn stover concentrated sulfuric acid saccharification. The concentration of sulfuric acid and the temperature of solubilization significantly affect corn stover decomposition. They also have significant effects on glucose and xylose recoveries. Low generation of furfural and 5-hydroxymethyl-2-furfural (5HMF) was noted and organic acids were the main by-products detected in the hydrolysate. Temperature also significantly affected the generation of levulinic acid and formic acid; however, acetic acid generation was not significantly influenced by all seven parameters. The ratio of acid to feedstock significantly affected glucose recovery, but not total sugar recovery. The corn stover hydrolysate was well fermented by both glucose- and xylose-fermenting yeast strains.

Hydrolysis of sweet sorghum bagasse and eucalyptus wood chips with liquid hot water

The chemical composition, hydrolysis products, and kinetics during liquid hot water pretreatment of sweet sorghum bagasse (SSB) and eucalyptus wood chips (EWC) were investigated. Under optimal conditions, a total xylose recovery of 79.6% and 55.6% for SSB and of 74.9% and 84.4% for EWC was achieved after pretreatments in a step-change flow rate reactor (184°C, 20ml/min, 8min, and 10ml/min, 10min) and batch stirred reactor (184°C, 5%w/v, 18min), respectively. More than 90% of the xylose was recovered as oligomers from SSB, independent of the type of reactor employed. The activation energies of xylan decomposition of SSB in the step-change flow rate reactor was 6.5-fold greater than that of EWC in the batch stirred reactor due to accumulation of acidic products. These findings show that sugar recovery is dependent on the reactor configuration for specific substrates.

Optimization of the enzymatic hydrolysis conditions of steam‐exploded wheat straw for maximum glucose and xylose recovery

AbstractBACKGROUND: The enzymatic hydrolysis of steam‐exploded wheat straw using commercial enzyme complexes has been studied. A cellulase enzyme complex (Accellerase 1500), along with specific xylanase complements (Accellerase‐XC and Accellerase‐XY) provided by Genencor, have been used to enhance glucose and xylose recovery.A systematic study with response surface methodology (RSM) was used to check the effect of the operating conditions: pH (4–5), temperature (50–60 °C) and enzyme/substrate ratio (0.1–0.5 mL gcellulose−1) on the enzymatic hydrolysis with Acellerase 1500 to maximize the sugar yield. Xylanases were used as complements to increase the release of xylose.RESULT: Statistical results from ANOVA analysis demonstrated that the enzymatic hydrolysis was clearly improved by temperature and enzyme/substrate ratio. The optimum conditions for higher glucose and xylose releases were obtained with the higher enzyme dosage ratio (0.5 mL g−1cellulose), 50 °C and pH 4.CONCLUSION: Model validation at optimum operating conditions showed good agreement between the experimental results and the predicted responses for a confidence level of 95%.The use of the xylanase complements, Accellerase‐XY (accessory xylanase enzyme complex) and Accellerase‐XC (accessory xylanase/cellulase enzyme complex), increases the conversion of hemicellulose. Accellerase‐XC supplementation was more effective, obtaining an increase in yields of glucose and xylose of 11.8% and 23.6%, respectively, using a dosage of 0.125 mL g−1cellulose. © 2012 Society of Chemical Industry

Biological conversion of forage sorghum biomass to ethanol by steam explosion pretreatment and simultaneous hydrolysis and fermentation at high solid content

In this work, forage sorghum biomass was studied as feedstock for ethanol production by a biological conversion process comprising the steps of hydrothermal steam explosion pretreatment, enzymatic hydrolysis with commercial enzymes, and fermentation with the yeast Saccharomyces cerevisiae. Steam explosion conditions were optimized using a response surface methodology considering temperature (180–230°C) and time (2–10 min). Sugar recovery in the pretreatment and the enzymatic digestibility of the pretreated solid were used to determine the optimum conditions, i.e., 220°C and 7 min. At these conditions, saccharification efficiency attained 89 % of the theoretical and the recovery of xylose in the prehydrolyzate accounted for 35 % of the amount of xylose present in raw material. Then, a simultaneous hydrolysis and fermentation (SSF) process was tested at laboratory scale on the solid fraction of forage sorghum pretreated at optimum condition, in order to evaluate ethanol production. The effect of the enzyme dose and the supplementation with xylanase enzyme of the cellulolytic enzyme cocktail was studied at increasing solid concentration up to 18 % (w/w) in SSF media. Results show good performance of SSF in all consistencies tested with a significant effect of increasing enzyme load in SSF yield and final ethanol concentration. Xylanase supplementation allows increasing solid concentration up to 18 % (w/w) with good SSF performance and final ethanol content of 55 g/l after 4–5 days. Based on this result, about 190 l of ethanol could be obtained from 1 t of untreated forage sorghum, which means a transformation yield of 85 % of the glucose contained in the feedstock.