Enzymatic Hydrolysis Of Wheat Straw Research Articles

Enhanced enzymatic hydrolysis of wheat straw by two-step pretreatment combining alkalization and adsorption.

Wheat straws (WS) were pretreated by a two-step pretreatment for enhanced enzymatic hydrolysis. The raw wheat straw (RWS) was firstly soaked in microwave-assisted NaOH solution at the presence of a mixed solution of H2O2 and hexadecyl trimethyl ammonium chloride (HTAC), and the residue was put into methyl orange (MO) solution to obtain the final substrate for enzymatic hydrolysis. It was interesting to find that the WS after the first step of the pretreatment could effectively remove MO in the second step of the pretreatment with the highest removal efficiency of 98.86% at the MO concentration of 25mg/L and at the adsorbent-adsorbate ratio of 0.8%. Meanwhile, the enzymatic hydrolysis efficiency of the WS that was pretreated by the two steps was higher than that of the RWS as well as the first-step-pretreated WS. Enzymatic hydrolysis experiment showed that the glucose concentration after 48-h hydrolysis was 4.85g/L at the solid loading of 5%, compared with the RWS of 0.90g/L and the first-step-pretreated WS of 4.33g/L. This suggested that the two-step pretreatment method could not only make WS as a good adsorbent but also a more biodegradable lignocellulosic material. Characterization analysis showed that the specific surface area and the cellulose content of the WS were both increased after the two-step pretreatment, indicating that the pretreatment method was significant to properly utilizing WS as biosorbent and biofuel. Besides, a possible mechanism for the effect of the pretreatment on the WS was proposed.

Use of wheat straw biomass in production of L-lactic acid applying biocatalysis and combined lactic acid bacteria strains belonging to the genus Lactobacillus

Abstract The aim of the study was to investigate the usability of wheat straw in the production of L-lactic acid via fermentation applying by newly isolated lactic acid bacteria (LAB) strains belonging to the genus Lactobacillus and its combinations. Biotreatment of wheat straw was carried out through a three-step procedure consisting of: (i) physical pre-treatment, (ii) enzymatic hydrolysis and (iii) fermentation with LAB strains under laboratory conditions. Lactic acid production, residual sugar, cell biomass, pH medium and the influence of ions such as magnesium, calcium and sodium on efficiency of enzymatic hydrolysis of wheat straw were the main features examined. Moreover, optimal parameters for enzymatic hydrolysis were selected. Increased lactic acid production was observed, when mixed LAB cultures were used in comparison to individual ones. The results confirmed that tested wheat straw could be used for lactic acid and L-lactic acid production using selected enzymes and combined LAB strains.

Effects and Mechanism of Metal Ions on Enzymatic Hydrolysis of Wheat Straw after Pretreatment

The effects and mechanism on the enzymatic hydrolysis of lignocellulose by metal ions were investigated by scanning electron microscopy (SEM), Fourier transform infrared spectroscopy (FTIR), dynamic light scattering (DLS), Fluorescence Spectra, and enzymatic kinetics and activity analyses of the enzymatic hydrolysis system. Fe3+ exerted the best enzymatic hydrolysis effect on pretreated wheat straw, and the highest reducing sugar conversion was 44.5%. SEM and FTIR indicated that alkali and ultrasonic pretreatments partially removed the lignin and hemicellulose from lignocellulose. DLS and fluorescence spectra results revealed that the electrostatic interaction between Fe3+ and the carboxyl group in the enzyme enlarged the enzyme’s steric structure. The data on enzymatic kinetics displayed that Fe3+ increased the maximum rate of reaction by 33.9% and the Michaelis-Menten by 5.72 g/L. The enzyme activity increase rate rose initially and then diminished, and the maximum increase rate was 36.1%.

Alkaline-assisted screw press pretreatment affecting enzymatic hydrolysis of wheat straw.

Screw press processing of biomass can be considered as a suitable mechanically based pretreatment for biofuel production since it disrupts the structure of lignocellulosic biomass with high shear and pressure forces. The combination with chemical treatment has been suggested to increase the conversion of lignocellulosic biomass to fermentable sugars. Within the study, the synergetic effect of alkaline (sodium hydroxide, NaOH) soaking and screw press pretreatment on wheat straw was evaluated based on, e.g., sugar recovery and energy efficiency. After alkaline soaking (at 0.1M for 30min) and sequential screw press pretreatment with various screw press configurations and modified screw barrel, the lignin content of pretreated wheat straw was quantified. In addition, the structure of pretreated wheat straw was investigated by scanning electron microscopy and measurement of specific surface area. It could be shown that removal of lignin is more important than increase of surface area of the biomass to reach a high sugar recovery. The rate constant of the enzymatic hydrolysis increased from 1.1×10-31/h for the non-treated material over 2.3×10-31/h for the alkaline-soaked material to 26.9×10-31/h for alkaline-assisted screw press pretreated material, indicating a nearly 25-fold improvement of the digestibility by the combined chemo-mechanical pretreatment. Finally, the screw configuration was found to be an important factor for improving the sugar recovery and for reducing the specific energy consumption of the screw press pretreatment.

The effect of direct and counter-current flow-through delignification on enzymatic hydrolysis of wheat straw, and flow limits due to compressibility.

This article compares the processes for wheat straw lignocellulose fractionation by percolation, counter-current progressing batch percolation and batch reaction at low NaOH-loadings (3-6% of DM). The flow-through processes were found to improve delignification and subsequent enzymatic saccharification, reduce NaOH-consumption and allow reduction of thermal severity, whereas hemicellulose dissolution was unaffected. However, contrary to previous expectations, a counter-current process did not provide additional benefits to regular percolation. The compressibility and flow properties of a straw bed were determined and used for simulation of the packing density profile and dynamic pressure in an industrial scale column. After dissolution of 30% of the straw DM by delignification, a pressure drop above 100 kPa m-1 led to clogging of the flow due to compaction of straw. Accordingly, the maximum applicable feed pressure and volumetric straw throughput was determined as a function of column height, indicating that a 10 m column can be operated at a maximum feed pressure of 530 kPa, corresponding to an operation time of 50 min and a throughput of 163 kg m-3 h-1 . Biotechnol. Bioeng. 2016;113: 2605-2613. © 2016 Wiley Periodicals, Inc.

Purification of Biorefinery Lignin with Alcohols

After hydrothermal pretreatment and enzymatic hydrolysis of wheat straw, a slurry rich in lignin but with a high content of inorganic substances, especially silica, and residual carbohydrates is produced. This slurry was used to develop an ethanol organosolv separation method to produce silica-free lignin fractions. The addition of para toluene sulphonic acid (PTSA) and the use of two alternative long-chain alcohols, oleyl alcohol or nonylphenol, were tested. In every reaction, two lignin fractions were produced and their molecular size and elemental composition were characterized. The yield of each fraction and the change in MWD were studied as a function of temperature and solid to liquid ratio. At 100, 150, and 200°C and with the use of PTSA, high-purity lignin fractions were obtained. After lignin fractionation with nonylphenol, a liquid silica-free product with high lignin content was obtained in yields between 17 and 72%.

Enhancement of enzymatic hydrolysis of wheat straw by gamma irradiation–alkaline pretreatment

Abstract Pretreatment of wheat straw with gamma irradiation and NaOH was performed to enhance the enzymatic hydrolysis of wheat straw for production of reducing sugar. The results showed that the irradiation of wheat straw at 50 kGy decreased the yield of reducing sugar, however, the reducing sugar yield increased with increasing dose from 50 kGy to 400 kGy. The irradiation of wheat straw at 100 kGy can significantly decrease NaOH consumption and treatment time. The reducing sugar yield could reach 72.67% after irradiation at 100 kGy and 2% NaOH treatment for 1 h. The combined pretreatment of wheat straw by gamma radiation and NaOH immersion can increase the solubilization of hemicellulose and lignin as well as the accessible surface area for enzyme molecules.

Efficient Pretreatment of Wheat Straw Using Novel Renewable Cholinium Ionic Liquids To Improve Enzymatic Saccharification

Nine cholinium ionic liquids (ILs) were synthesized. A high solubility of lignin (up to 483 mg g–1) and xylan (up to 721 mg g–1) was observed in four ILs containing organic anions, while cellulose, chitosan, and keratin were scarcely soluble in all ILs. These ILs were used for wheat straw pretreatment. Among the nine ILs tested, cholinium taurate ([Ch][Tau]) was the best. The effects of biomass particle sizes, water contents, and biomass loadings on the IL pretreatment were studied. Readily digestible residues were obtained after wheat straw up to 2 mm size was pretreated. Additionally, this IL pretreatment process was highly tolerant toward moisture. A good reducing sugar yield (79.7%) was achieved in the enzymatic hydrolysis of wheat straw pretreated by [Ch][Tau] at a biomass loading of 10% under 80 °C for 6 h. Therefore, renewable sulfonate-based cholinium ILs may be promising solvents for pretreatment and fractionation of lignocelluloses.

Sugar production from wheat straw biomass by alkaline extrusion and enzymatic hydrolysis

One characteristic necessary to make ethanol production from biomass economically feasible is to optimize enzymatic dosage, since enzymes production is expensive. This work investigated the efficacy of different enzymes dosages and solid loadings on wheat straw enzymatic hydrolysis, aimed at obtaining process conditions that lead to good sugars yields from pretreated material. Alkaline extrusion was employed as pretreatment at 70 °C and 10% NaOH solution (w/v). Enzymatic hydrolysis was performed at 5, 10, 15 and 20% solids loading (w/v). Enzyme doses ranged from 6.92 to 20 FPU/g of glucan. Cellulase was also supplemented with xylanase at various proportions. Alkaline extrusion provided a substrate easier to hydrolyze than untreated material. Even the assay with the lowest enzyme dosage (6.92 FPU) achieved a good carbohydrate hydrolysis yield in relation to the theoretical; the glucose yield was 73.8% and xylose yield was 82.8%. A medium containing 100 g/L of fermentable sugar was obtained at 20% solids loading (w/v) and 20 FPU/g of glucan. The supplementation of cellulase with xylanase at U to FPU activity ratio of 3.11:1 improved the glucose yield about 21% over the assay with no xylanase.

Rapid estimation of sugar release from winter wheat straw during bioethanol production using FTIR-photoacoustic spectroscopy.

BackgroundComplexity and high cost are the main limitations for high-throughput screening methods for the estimation of the sugar release from plant materials during bioethanol production. In addition, it is important that we improve our understanding of the mechanisms by which different chemical components are affecting the degradability of plant material. In this study, Fourier transform infrared photoacoustic spectroscopy (FTIR-PAS) was combined with advanced chemometrics to develop calibration models predicting the amount of sugars released after pretreatment and enzymatic hydrolysis of wheat straw during bioethanol production, and the spectra were analysed to identify components associated with recalcitrance.ResultsA total of 1122 wheat straw samples from nine different locations in Denmark and one location in the United Kingdom, spanning a large variation in genetic material and environmental conditions during growth, were analysed. The FTIR-PAS spectra of non-pretreated wheat straw were correlated with the measured sugar release, determined by a high-throughput pretreatment and enzymatic hydrolysis (HTPH) assay. A partial least square regression (PLSR) calibration model predicting the glucose and xylose release was developed. The interpretation of the regression coefficients revealed a positive correlation between the released glucose and xylose with easily hydrolysable compounds, such as amorphous cellulose and hemicellulose. Additionally, a negative correlation with crystalline cellulose and lignin, which inhibits cellulose and hemicellulose hydrolysis, was observed.ConclusionsFTIR-PAS was used as a reliable method for the rapid estimation of sugar release during bioethanol production. The spectra revealed that lignin inhibited the hydrolysis of polysaccharides into monomers, while the crystallinity of cellulose retarded its hydrolysis into glucose. Amorphous cellulose and xylans were found to contribute significantly to the released amounts of glucose and xylose, respectively.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0267-2) contains supplementary material, which is available to authorized users.

A comparison of several organosolv pretreatments for improving the enzymatic hydrolysis of wheat straw: Substrate digestibility, fermentability and structural features

Abstract Four organosolv pretreatment processes, namely Formiline, Acetoline, sulfuric acid-catalyzed ethanol (SACE) and auto-catalyzed ethanol (ACE) pretreatments were used to pretreat wheat straw under respective optimal conditions. Comparative studies were performed in terms of the enzymatic digestibility of cellulosic solids, simultaneous saccharification and fermentation (SSF) for ethanol production, mass balance analysis and structural features of the pretreated solids. The results indicated that Formiline and Acetoline pretreatments showed higher degrees of delignification, lower xylose degradation and lower solid glucan recoveries than SACE and ACE processes. The SACE and ACE pretreated solids still had high lignin contents but demonstrated higher initial enzymatic hydrolysis rates than Formiline and Acetoline pretreated solids. Formiline pretreatment obtained the highest final enzymatic glucan conversion, glucose concentration and ethanol yield, while Acetoline pretreatment obtained the lowest. After organosolv pretreatment, the compact and beehive-like cell wall structure was disrupted and cellulose fibers became separated. The SACE and ACE pretreated solids showed more depositions on fiber surface, which probably came from the condensation and precipitation of lignin.

Sequential pretreatment strategies under mild conditions for efficient enzymatic hydrolysis of wheat straw.

This work studies the sequential execution of dilute sulfuric acid (DAP) (0.1-0.75 %, v/v) and dilute sodium hydroxide (AKP) (0.25-3 %, w/v) [i.e., DAP followed by AKP (DAP+AKP) and vice versa (AKP+DAP)] at low temperatures (<121 °C) and short reaction times (5-60 min) for maximizing sugar recovery in the enzymatic hydrolysis of wheat straw with low enzyme dosage. The pretreatment effectiveness was measured by the sum of the severity factors of both pretreatments and the saccharification yield achieved in the subsequent stage of enzymatic hydrolysis. Degradation compounds were quantified and mass balance calculations were carried out for each pretreatment sequence to verify the correct account of the input biomass and output products. Results show that sequential pretreatments (AKP+DAP and DAP+AKP) had a positive effect in enzyme accessibility thus improving monosaccharide yields compared to single DAP and AKP pretreatments. DAP+AKP achieved a high xylose yield (ca. 0.867 of theoretical) at the DAP stage, while no xylose monosaccharides were detected in the subsequent AKP. After enzyme saccharification of double-pretreated solids, the total monosaccharide yield was 0.786 (of theoretical). For AKP+DAP sequence, lower results were obtained (total monosaccharide yield 0.783 of theoretical). Sequential pretreatments total yields increased by 21 % compared to single pretreatments. AKP removed more than half of the lignin from the wheat straw in all cases. Acid and alkali concentrations played a relevant role in all pretreatment sequences, while reaction time and temperature were less important with an almost-linear effect on the total monosaccharide yields.

Yield optimization and rational function modelling of enzymatic hydrolysis of wheat straw pretreated by NaOH-delignification, autohydrolysis and their combination

The sugar yield of saccharification processes must be optimized against productivity, for which rational function modelling provides a smooth solution.

CELLULASES PRODUCTION UNDER SOLID STATE FERMENTATION USING AGRO WASTE AS A SUBSTRATE AND ITS APPLICATION IN SACCHARIFICATION BY TRAMETES HIRSUTA NCIM

Food and energy crisis are the biggest constraint all over the world which has focused lights on need of utilizing renewable resources to meet the future demand. A promising strategy is efficient utilization of lignocellulosic waste and fermentation of the resulting sugars for production of desired metabolites or biofuel. Production of all the cellulase enzymes on wheat bran and different parameters regulating it like pH, moisture ratio (substrate: liquid), temperature and inoculum size has been optimized which found to be 4.5, 1:3, 30°C and 108 spores respectively. Salient feature of partially purified enzyme with stability in the range of 30-50°C under acidic pH range was found to be prominent for industrial applications, moreover in this study, Trametes hirsuta, an efficient cellulase producer, was observed to be an effective species for saccharification of wheat straw to enhance the sugar yield. Enzymatic hydrolysis of wheat straw with 15 FPU of cellulase from the species showed 73% yield in 20 hrs. It may prove to be a suitable choice for the industrial saccharification of lignocellulosic biomasses.

Effects of different pre-extractions combining with chemi-thermomechanical treatments on the enzymatic hydrolysis of wheat straw

Three different pre-extraction methods (i.e., acetic acid, sulfuric acid and sodium hydroxide) were used for the pretreatment followed by chemi-thermomechanical treatments and then enzymatic hydrolysis of wheat straw to produce fermentable sugars. The performance of enzymatic hydrolysis by the synergistic effect of pre-extractions and chemi-thermomechanical treatments was remarkable. Results showed that the pre-extraction combining with the chemi-thermomechanical treatments shorten the enzymatic hydrolysis time and improved the glucose yield at the same enzyme loadings. The chemical components, swelling ability, and crystallinity, as well as the surface morphology of the substrates were changed obviously. All of these changes can affect the accessibility of enzymes to cellulose in the substrates to a certain extent.

Evaluation of Selected White-Rot Fungal Isolates for Improving the Sugar Yield from Wheat Straw

Biological pretreatment of lignocellulosic biomass by fungi can represent a low-cost and eco-friendly alternative to physicochemical methods to facilitate enzymatic hydrolysis. However, fungal metabolism can cause cellulose loss and it is therefore necessary to use the appropriate fungal strain-biomass type combination. In this work, the effects of biological pretreatments carried out by five different fungi on enzymatic hydrolysis of wheat straw were investigated. The best results were obtained with a Ceriporiopsis subvermispora strain, which minimized weight and cellulose losses and gave the highest net sugar yield (calculated with respect to the holocellulose content of the untreated straw), up to 44 % after a 10-week pretreatment, more than doubling the yields obtained with the other isolates. Moreover, prolonging the pretreatment from 4 up to 10 weeks produced a 2-fold increase, up to 60 %, in digestibility (sugar yield, calculated considering the holocellulose content of the pretreated material). The hemicellulose content of the pretreated material resulted inversely correlated with digestibility, and it could thus be utilized as an index of the pretreatment efficacy. Finally, a correlation was also found between digestibility and the difference between the absorbance values at 290 and 320 nm of pretreated wheat straw extracts.

Effect of dilute acid pretreatment conditions and washing on the production of inhibitors and on recovery of sugars during wheat straw enzymatic hydrolysis

Pretreatment is an essential process to break down recalcitrant biomass and dilute acid hydrolysis is one of the most efficient and cost effective pretreatment technologies available today. However there are potential disadvantages in using dilute acid as a pretreatment, such as the production of degradation products, which inhibits the ensuing processing chain and limits its adoption. In this work, wheat straw was pretreated under varying dilute acid conditions; the resulting degradation products were determined and the quality of sugar stream generated via enzymatic saccharification was monitored. The dilute acid pretreatment conditions were: temperatures of 140 and 160 °C, sulfuric acid concentrations of 5, 10 and 20 dm3 m−3 and reaction times of 10, 20, 30, 45 and 60 min. Pretreated wheat straw was washed with six dilutions of water and hydrolyzed with commercial cellulase enzymes for 24–48 h. Optimal conditions for pretreating wheat straw were determined as: 140 °C, 10 dm3 m−3 sulfuric acid concentration and a 30 min reaction time. At these conditions, the glucose yield from wheat straw was maximized at 89% of the theoretical maximum, while the concentrations of formic acid, furfural, acetic acid and 5-hydroxymethylfurfural were 32.37 ± 4.91, 12.08 ± 1.69, 7.98 ± 1.02 and 1.14 ± 0.22 g kg−1, respectively. Increases in pretreatment severity led to increases in inhibitor generation, as well as a 27% reduction in monosaccharide yield. Rinsing with deionized water was effective in removing inhibitors, such as 86% of furfural. The formation of inhibitors was thus observed to depend on dilute acid pretreatment conditions.

Combined Severity during Pretreatment Chemical and Temperature on the Saccharification of Wheat Straw using Acids and Alkalis of Differing Strength

Acids and alkalis are considered important catalysts in biomass pretreatment, which is essential to overcome the recalcitrance of lignocellulose for sugar release. In this study, the effects of various chemicals and temperatures on the pretreatment and subsequent enzymatic hydrolysis of wheat straw were investigated. The conversions of glucan and xylan during pretreatment and enzymatic hydrolysis were examined. The temperature and different ions in pretreatment govern the dissociation constant and hydrogen ion concentration. Due to higher dissociation at higher temperature, weak acids and weak alkalis can produce high glucose yields, similar to strong acids and alkalis. The concept of modified combined severity for weak acid pretreatment was explored. The pH value and real combined severity of weak acids at reaction temperatures were estimated according to xylan recovery during pretreatment. Glucose yield in enzymatic hydrolysis is mainly decided by xylan recovery for acidic pretreatment and by total content of xylan and acid-insoluble-lignin in solids for alkaline pretreatment.

Improved enzymatic hydrolysis of wheat straw by combined use of gamma ray and dilute acid for bioethanol production

Pretreating wheat straw with a combination of dilute acid and gamma irradiation was performed in an attempt to enhance the enzymatic hydrolysis for bioethanol production. The glucose yield was significantly affected by combined pretreatment (3% sulfuric acid-gamma irradiation), compared with untreated wheat straw and individual pretreatment. The increasing enzymatic hydrolysis after combined pretreatment is resulting from decrease in crystallinity of cellulose, loss of hemicelluloses, and removal or modification of lignin. Therefore, combined pretreatment is one of the most effective methods for enhancing the enzymatic hydrolysis of wheat straw biomass.

Characterization of a Novel Dye-Decolorizing Peroxidase (DyP)-Type Enzyme from Irpex lacteus and Its Application in Enzymatic Hydrolysis of Wheat Straw

Irpex lacteus is a white rot basidiomycete proposed for a wide spectrum of biotechnological applications which presents an interesting, but still scarcely known, enzymatic oxidative system. Among these enzymes, the production, purification, and identification of a new dye-decolorizing peroxidase (DyP)-type enzyme, as well as its physico-chemical, spectroscopic, and catalytic properties, are described in the current work. According to its N-terminal sequence and peptide mass fingerprinting analyses, I. lacteus DyP showed high homology (>95%) with the hypothetical (not isolated or characterized) protein cpop21 from an unidentified species of the family Polyporaceae. The enzyme had a low optimal pH, was very stable to acid pH and temperature, and showed improved activity and stability at high H2O2 concentrations compared to other peroxidases. Other attractive features of I. lacteus DyP were its high catalytic efficiency oxidizing the recalcitrant anthraquinone and azo dyes assayed (kcat/Km of 1.6 × 10(6) s(-1) M(-1)) and its ability to oxidize nonphenolic aromatic compounds like veratryl alcohol. In addition, the effect of this DyP during the enzymatic hydrolysis of wheat straw was checked. The results suggest that I. lacteus DyP displayed a synergistic action with cellulases during the hydrolysis of wheat straw, increasing significantly the fermentable glucose recoveries from this substrate. These data show a promising biotechnological potential for this enzyme.