Saccharification Of Rice Straw Research Articles

Microwave-assisted ternary deep eutectic solvent pretreatment for improved rice straw saccharification under mild pretreatment conditions

The development of a green and cost-effective pretreatment method to overcome biomass recalcitrance is a challenging assignment for the efficient valorization of lignocellulosic compounds. In this study, a ternary deep eutectic solvent (DES) consisting of choline chloride (ChCl), p-toluene sulfonic acid (pTSA) and ethylene glycol (EG) was applied in rice straw (RS) pretreatment under microwave (MW) irradiation for the further conversion of the polysaccharide fraction. The effect of the pretreatment temperature, time and pTSA content in the DES on lignin extraction and polysaccharide hydrolysis was assessed by a central composite design (CCD). Under the selected pretreatment conditions (80 ºC, 22.5 min, ChCl:pTSA:EG 1:1:9), 61.6% delignification was achieved, as well as nearly complete conversion of the initial glucan in RS (93.4% glucose yield) and a good xylan conversion rate (48.3% xylose yield), representing a total polysaccharide exploitation of 78.3%. Energetical requirement was remarkably lower compared to conventional conductive heating. Importantly, the ternary DES showed good recyclability pattern after two reuses. Overall, this study demonstrated the potential of MW-assisted ternary DES pretreatment for improved valorization of biomass polysaccharides under mild pretreatment conditions, representing an efficient and energetical-saving alternative pathway within the biorefinery framework.

Improved saccharification of rice straw by removing phenolic compounds using a stable immobilized metagenome-derived laccase on sodium alginate-based hydrogel

Laccases can biodegrade lignocellulosic agricultural waste, which has a recalcitrant structure hindering industrial biomass hydrolysis. In the context of biomass decomposition, introduction of a stabilized enzyme with enhanced performance is of critical importance. This study aimed to stabilize laccase, obtained from tannery metagenome (PersiLac2) on sodium alginate-based hydrogels. The immobilized laccase remained stable in the acidic and alkaline pH ranges and preserved over 79.39 % of its initial activity at pH 4.0–9.0. Similarly, immobilized enzyme improved laccase activity at high temperatures, which is crucial in biorefinery processes, and the immobilized enzyme demonstrated 88.35 % activity at 80 ºC. The immobilization of laccase on hydrogels effectively prevented enzyme leaching and rendered it easier to separate and recycle, showing 58.74 % laccase activity after 15 cycles. The efficiency of immobilized PersiLac2 in enzymatic hydrolysis of rice straw was evaluated to enhance the generation of fermentable sugars, saccharification, and phenol reduction. Laccase treatment of rice straw resulted in an excellent saccharification yield and liberation of reducing sugars and removed 77.19 % of phenols during hydrolysis. The depolymerization effect of free and immobilized laccase on rice straw was investigated by FTIR and SEM analyses which confirmed efficient structural disruption by immobilization. The results indicated the potential of immobilized Persilac2 to degrade the compact wrap of lignin–carbohydrate complex in lignocellulosic substrates and its application in biomass-based industries.

Microwave-assisted alkali pre-treatment medium for fractionation of rice straw and catalytic conversion to value-added 5-hydroxymethyl furfural and lignin production

In the current study, the use of microwave-assisted sodium hydroxide medium (MWSH) for pre-treatment and saccharification of rice straw to obtain sugar syrup for the production of 5-hydroxymethyl furfural (5-HMF) was investigated. The optimization of the MWSH pre-treatment was carried out using central composite methodology, resulting in a maximum reducing sugar yield of 350 mg/g of treated rice straw (TRS) and a glucose yield of 255 mg/g of TRS under the conditions of a microwave power of 681 W, a NaOH concentration of 0.54 M, and a pre-treatment time of 3 min. Additionally, the microwave assisted transformation of sugar syrup with titanium magnetic silica nanoparticle as catalyst, producing 41.1 % yield of 5-HMF from the sugar syrup after 30 min microwave irradiation at 120 °C with catalyst loading of 2.0:200 (w/v)). The structural characterization of the lignin was analysed using 1H NMR techniques, and the surface carbon (C1s spectra) and oxygen (O1s spectra) composition changes of the rice straw during pre-treatment were analysed using X-ray photoelectron spectroscopy. The rice straw based bio-refinery process which contains MWSH pretreatment followed by dehydration of sugars achieved high efficiency of 5-HMF production.

Cellulase production by Myceliophthora thermophila in solid state fermentation and its utility in saccharification of rice straw

在固态发酵中研究了嗜热B展示了嗜热毁丝，JTLRMDU3连续连续生产55个霉菌的优化。嗜热毁丝，产生最大的霉菌（45.81 U/g DMR）。81 U/g DMR），1:3，水活度为 0.95，硫酸铵 (0.5%) 和 20000 (0.5%) 45 °C 下使用 5 天 PEG 在“一次”的变量中。进一步添加Tween-20 (0.5%) 和 K 2 HPO 4 (0.25%) 可提高SSF 中嗜热菌的后续发酵发酵产量（56.06 U/g DMR）。部分精制的嗜热分枝菌的发酵酶发酵量（20 U），与未经处理的生物质相对，碳酸钠的稻草在 24 小时（203.91 mg/g 底物）后，在 pH 5.0（185.56 mg/g/g 底物）和 60 °C（190.83 mg/g 底物）下释放出最大的糖还原碳还原稻草中释放的糖未经处理的稻草。

Prospects of utilizing seawater as a reaction medium for pretreatment and saccharification of rice straw

The transition towards a bio-based economy has led to an unprecedented surge in fresh water consumption that renders biofuel a high water footprint product. The depleting fresh water resources have exacerbated the situation which necessitates the exploration of non-potable water for biorefinery purposes. In the current study, seawater is used as a plausible alternative reaction medium for pretreatment and saccharification of rice straw. Response Surface Methodology (RSM) based on Box-Behnken Design (BBD) was employed to model, predict and validate cellulose release and reducing sugar yield from rice straw subjected to microwave-NaOH pretreatment. The optimized pretreatment conditions were determined to be 8.54% substrate loading, 1.94% NaOH and 4.09 min which resulted in the maximum cellulose release of 65.43% and reducing sugar yield of 0.554 g/g. Several physico-chemical studies of the raw and pretreated biomass were carried out using bomb calorimetry, scanning electron microscopy (SEM), Fourier transform infrared (FTIR) spectroscopy, Brunauer–Emmett–Teller (BET) analysis and thermal gravimetric analysis (TGA) to examine the efficacy of pretreatment. Evidences of an apparent delignification was substantiated by the increase in surface area from 7.719 to 44.188 m2 g−1and pore volume from 0.039 to 0.071 mlg−1 which was consistent with the decrease in energy density and distorted surface morphology of the pretreated biomass. Further, the FTIR revealed a reduced peak in the absorption spectral bands at 1636 cm−1 which confirmed the pretreatment mediated degradation of lignin and hemicellulose. This finding provides evidence on the prospects of utilizing abundantly available seawater resource as a reaction medium for sustainable biofuel production.

Biocatalytic pretreatment of rice straw by ligninolytic enzymes produced by newly isolated Micrococcus unnanensis strain B4 for downstream cellulolytic saccharification.

Rice (Oryza sativa L.) straw is an agricultural byproduct of high yield, and its disposal by burning has detrimental effect on ecosystem. It has potential as source of fermentable sugars for industrial use; however, it requires effective pretreatment to remove lignin. Bacterial enzymes based pretreatment is advantageous due to their extracellular nature, and tolerance to higher temperature, pH and oxygen limitation. We herein report screening of lignocellulose degradation environment of vermicompost for ligninolytic bacteria, and studying role of Micrococcus unnanensis strain B4 in delignification of rice straw. The bacterium was capable to degrade acid soluble and insoluble lignin; and produced lignin degrading laccase and peroxidase having maximum activity at pH 6.5 and 72 h incubation. Both enzymes exhibited alkaline pH stability, and thermal stability with retention of 100 % activity on pre-incubation at 60 ℃ for 1 h. The enzymes were used for pretreatment of rice straw using chemicals (acetic acid:hydrogen peroxide) pretreatment as reference. Scanning electron microscopy of pretreated rice straw samples showed alteration in morphology with exposure of cellulosic components. Enzymatically pretreated rice straw on saccharification by a commercial cellulase yielded about 400 mg of reducing sugar per gram, comparable to that released on chemical pretreatment. Hence, pretreatment based on M.unnanensis strain B4 and its ligninolytic enzymes can be an alternative to chemical pretreatment for saccharification of rice straw to fermentable sugars.

The combined effect of inorganic salt and ionic liquid in pretreatment on enzymatic saccharification of rice straw

The pretreatment method is one of the challenging steps in the production of biofuel through the biorefinery process that unlocks the recalcitrant nature of lignocellulosic biomass. Ionic liquid pretreatment gained attention for being highly effective to improve the enzymatic saccharification of the biomass, however its high cost hinders its industrial application. In this study, the combined effect of ionic liquid 1- ethyl-3-methylimidazolium acetate (EMIM-Ac) with inorganic salts (NaCl and KCl) was used for the pretreatment of rice straw. Optimization of pretreatment was conducted based on Response Surface Methodology and sugar yields obtained by EMIM-Ac+NaCl (160 °C, 88.7 min, 7.6%wt) and EMIMAc+ KCl (160 °C, 68.2 min, 12.5%wt) were 670.7 and 392.9 mg/g-biomass, respectively. The effect of combined pretreatment on ethanol production was analyzed after 48h fermentation. The results showed that the ethanol yield from pretreated samples with EMIM-Ac+NaCl (0.72%) and EMIM+KCl (0.76%) was increased by 2.18 and 2.25 fold times, respectively, compared to untreated sample (0.33%). This combined effect of inorganic salts and ionic liquid significantly removed the lignin during pretreatment, while maintaining efficient enzymatic saccharification of rice straw. Thus, this cost-effective combined chemical method may be an alternative strategy for increasing cellulosic ethanol production.

Efficient saccharification of ionic liquid-pretreated rice straw in a one-pot system using novel metagenomics derived cellulases

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

Simultaneous Biological Pretreatment and Saccharification of Rice Straw by Ligninolytic Enzymes from Panus neostrigosus I9 and Commercial Cellulase.

The utilization of rice straw for biofuel production is limited by its composition. The pretreatment process is required to improve the enzymatic accessibility of polysaccharides in the biomass prior to enzymatic saccharification. In this study, simultaneous biological pretreatment and saccharification (SPS) of rice straw starting from laccase production by Panus neostrigosus I9 was operated in a 2-L fermenter. It was found that fungal physiology was strongly influenced by the agitation, and that the highest laccase production was obtained at an agitation speed of 750 rpm (209.96 ± 0.34 U/L). The dilution rate of 0.05 h−1 was set in continuous fermentation which resulted in laccase activity of 678.49 ± 20.39 U/L, approximately three times higher than that in batch culture. Response surface methodology (RSM) was applied to achieve the condition for maximum percentage of delignification. The maximum percentage of delignification of 45.55% was accomplished after pretreatment of rice straw with laccase enzyme 39.40 U/g rice straw at 43.70 °C for 11.19 h. Reducing sugar of 3.85 ± 0.15 g/L was obtained from the digested rice straw in a SPS reactor, while non-pretreated rice straw gave only 1.13 ± 0.10 g/L within 12 h of incubation. The results indicated that simultaneous biological pretreatment and saccharification (SPS) of rice straw by laccase helped to improve the accessibility of cellulose by cellulolytic enzymes.

Thermoxylanolytic and Thermosaccharolytic Potential of a Heat Adapted Bacterial Consortium Developed From Goat Rumen Contents

Thermoactive xylanases have important applications in the industrial deconstruction of lignocellulosic plant biomass, due to their sustained activity even at high temperature conditions of industrial bioreactors. We herein report the development of a thermoactive xylanolytic microbial consortium from the semi-digested contents of goat rumen and characterization of the xylanolytic enzyme cocktail produced by it. The consortium exhibited maximum endoxylanase activity at pH6 and at 60°C. Zymogram analysis revealed the production of multiple xylanases. The xylanase cocktail was stable over a pH range of 5–9 after pre-incubation for 3 h. It retained 74% activity after pre-incubation (60°C) for 50 min. It’s activity was enhanced in presence of β-mercaptoethanol, NH4+, Mg2⁺ and Ca2⁺, whereas Hg2⁺ had an inhibitory effect. The xylanolytic cocktail was further utilized for the saccharification of alkali pre-treated rice straw and mushroom spent rice straw. Saccharification was studied quantitatively using the dinitrosalicylic acid method and qualitatively using scanning electron microscopy. Results indicated the potential of the xylanolytic cocktail for the saccharification of rice straw and highlighted the significance of chemical and/or biological pre-treatment in improving the accessibility of the substrate towards the xylanase cocktail.

A greener, mild, and efficient bioprocess for the pretreatment and saccharification of rice straw

Open rice straw burning has created hazardous effects on the environment and human health. Biological pretreatment of rice straw has been proven as an environmental-benign and economical feasible process for the production of biofuels and value-added products under milder and greener conditions by avoiding harmful chemicals and toxic reagents. A consolidated bioprocess for the production of cellulolytic enzymes and biological pretreatment was developed to achieve a cost-effective saccharification of rice straw. Biodegradation of biomass was slightly enhanced with increase in cultivation time of microbial pretreatment. Furthermore, the modification in biomass due to biological pretreatment weakened the interaction between hemicellulose and lignin that resulted in significant reduction in lignin using Bacillus subtilis subsp. subtilis JJBS300, Myceliophthora thermophila BJTLRMDU3, and Aspergillus oryzae SBS50 for biological pretreatment of rice straw. Bacterial culture produced maximum FPase, CMCase, and β-glucosidase of 28, 17, and 20.36 U/g DMR after 2 days during pretreatment process, whereas M. thermophila produced maximum FPase (85.10 U/g DMR), CMCase (96.89 U/g DMR), and β-glucosidase (91.92 U/g DMR) after 9 days. The mold A.oryzae SBS50 also produced maximum FPase (57.41 U/g DMR), CMCase (55.36 U/g DMR), and β-glucosidase (48.04 U/g DMR) after 9 days of pretreatment. Maximum amount of reducing sugars of 52.41, 86.74, and 49.59 mg/g substrate were liberated from 6-, 5-, and 3-day-old biological pretreated rice straw by B. subtilis, M. thermophila, and A. oryzae, respectively, after enzymatic hydrolysis for 6 h at 60 oC and pH 5.0. Laccase-pretreated rice straw followed by enzymastic saccharification resulted in liberation of 162.82 mg/g reducing sugars at pH 5.0 and 60 °C after 6h using 20 U/g cellulase. Simultaneous laccase pretreatment and saccharification (SLPS) process further enhanced the liberated reducing sugars, i.e., 179.47 mg/g substrate. FTIR, XRD, and SEM analyses showed marked morphological changes as a result of delignification after biological pretreatment of rice straw. Biological pretreatment being an environmental-benign process causing no harm to the environment in comparison to physical and chemical pretreatments of lignocellulosic biomass could be a better pretreatment strategy for bioremediation of lignocellulosic substrates.

Mutagenesis of UDP-xylose epimerase and xylan arabinosyl-transferase decreases arabinose content and improves saccharification of rice straw.

Rice straw is an important renewable biomass resource. However, due to its slow degradation returning to the field, and the environmental pollution of conventional straw burning, it is highly desired for more efficient utilization of rice straw resource. The complex structure of rice cell wall composition impedes the efficient utilization of straw biomass.

Biochemical characteristics of a novel ethanol-tolerant xylanase from Bacillus subtilis subsp. subtilis JJBS250 and its applicability in saccharification of rice straw

The present study reports the partial purification and characterisation of a novel xylanase from Bacillus subtilis subsp. subtilis JJBS250 followed by its applicability in the saccharification of rice straw. Bacterial xylanase was partially purified by gel filtration chromatography using Sephadax G-50 matrix that displayed optimal activity at 60 °C and pH 7.0 with half-life values of 1420 and 718 min at 60 °C and 80 °C, respectively. Bacterial xylanase showed high tolerance to ethanol with Km and Vmax values of 1.62 mg/ml and 23.92 U/ml, respectively, for beechwood xylan. Maximum amount of reducing sugars was obtained from sodium carbonate pretreated rice straw (151.65 mg/g substrate) as compared to untreated biomass (90.49 mg/g substrate) using 20 U/g enzyme dose at 60 °C and pH 7.0 after 48 h. Furthermore, the saccharification of pretreated rice straw was improved by synergistic action of bacterial and fungal xylanases. Analysis of rice straw using scanning electron microscopy (SEM), x-ray diffraction (XRD) and Fourier transform infrared (FTIR) spectroscopy clearly showed the morphological changes and delignification in rice straw after pretreatment. Bacterial xylanase exhibiting novel properties including ethanol tolerance and high thermostability is highly suitable for the production of second generation biofuels in simultaneous saccharification and fermentation process using lignocellulosic substrates.

Rice straw saccharification using cellulolytic cocktail from Aspergillus tubingensis and structure alterations studies of the wall polymer

Optimization of saccharification of rice straw plays a crucial role in harnessing maximum fermentable sugars through enzymatic hydrolysis of this complex polymer. The present study was aimed to evaluate the applicability of A. tubingensis NKBP-55 cellulolytic cocktail for generation of fermentable sugars and to carry out parametric optimization of the saccharification process followed by batch ethanolic fermentation of the rice straw hydrolysate. Also, evaluation of the alterations (composition, crystallinity and structural morphology) occurring in the wall polymer structure after sequential treatments was studied. The cellulolytic cocktail, under the statistically optimized conditions (rice straw 4% w/v and pH 5.0) liberated 578 mg fermentable sugars (glucose 463 mg, xylose 114.35 and cellobiose 0.71 mg) per gram of pretreated rice straw showing 2.17-fold enhancement. Candida shehatae NCIM 3501 utilized both glucose and xylose and produced 16.15 g/L bioethanol along with yield (YP/S) 0.50 after 24 h of fermentation. Its bioethanol production was observed to be better than Saccharomyces cerevisiae (13.39 g/L) and their co-culture (15.57 g/L). Sequential changes brought about by the enzymatic treatment of the solid substrate revealed by X-ray diffraction and FTIR analyses showed decrease in the absolute crystallinity (CrI) (54.80 to 48.31%) and total crystallinity index (TCI) (1.002 to 0.991) and confirmed the degradation of the crystalline domain of cellulose by enzyme. The study demonstrated the potential of cellulolytic cocktail produced by A. tubingensis NKBP-55 in rice straw saccharification and its efficient fermentation by conventional and xylose-fermenting yeast in batch ethanolic fermentation.

Improvement of potassium permanganate pretreatment by enzymatic saccharification of rice straw for production of biofuels

Commonly, the agricultural waste, i.e. lignocellulosic biomass is disposed through combustion causing air pollution with production of PM2.5 and PM10 particles. However, it has been found that these biomasses can be used as source for the production of biofuels and other valuable biochemicals. Though deconstruction of lignocellulosic biomass is challenging due to its complex structure. In this study, rice straw (RS) was pretreated using potassium permanganate (KMnO4) to enhance the enzymatic saccharification efficiency. The study was carried out by varying the operational factors in pretreatment, including temperature (30-90°C), time (30-360 min) and concentration of KMnO4 (0.5-3.0, % w/v), respectively, based on Box-Behnken design (BBD). Through multi-regression analysis of the experimental data obtained after pretreatment, the optimum conditions were determined. The optimum conditions for temperature, time and potassium permanganate concentration were 48.09°C, 360 min, and 1.36% w/v, respectively. The saccharifications of pretreatment and untreated rice straw were carried out using Cellic Ctec2. The reducing sugar was determined by using DNS method and the yields of the untreated and pretreated RS were 32.38 and 49.011 mg/mL, respectively. The results showed that the sugar for pretreated RS were 1.51 fold times higher compared to untreated RS. Therefore, this work illustrates the pretreatment efficiency for KMnO4 to enhance the reducing sugar yield during saccharification, which can be used for biofuel and value-added product productions.

Association mapping identifies quantitative trait loci (QTL) for digestibility in rice straw

BackgroundThe conversion of lignocellulosic biomass from agricultural waste into biofuels and chemicals is considered a promising way to provide sustainable low carbon products without compromising food security. However, the use of lignocellulosic biomass for biofuel and chemical production is limited by the cost-effectiveness of the production process due to its recalcitrance to enzymatic hydrolysis and fermentable sugar release (i.e., saccharification). Rice straw is a particularly attractive feedstock because millions of tons are currently burned in the field each year for disposal. The aim of this study was to explore the underlying natural genetic variation that impacts the recalcitrance of rice (Oryza sativa) straw to enzymatic saccharification. Ultimately, we wanted to investigate whether we could identify genetic markers that could be used in rice breeding to improve commercial cultivars for this trait. Here, we describe the development and characterization of a Vietnamese rice genome-wide association panel, high-throughput analysis of rice straw saccharification and lignin content, and the results from preliminary genome-wide association studies (GWAS) of the combined data sets. We identify both QTL and plausible candidate genes that may have an impact on the saccharification of rice straw.ResultsWe assembled a diversity panel comprising 151 rice genotypes (Indica and Japonica types) from commercial, historical elite cultivars, and traditional landraces grown in Vietnam. The diversity panel was genotyped using genotype by sequencing (GBS) methods yielding a total of 328,915 single nucleotide polymorphisms (SNPs). We collected phenotypic data from stems of these 151 genotypes for biomass saccharification and lignin content. Using GWAS on the indica genotypes over 2 years we identified ten significant QTL for saccharification (digestibility) and seven significant QTL for lignin. One QTL on chromosome 11 occurred in both GWAS for digestibility and for lignin. Seven QTL for digestibility, on CH2, CH6, CH7, CH8, and CH11, were observed in both years of the study. The QTL regions for saccharification include three potential candidate genes that have been previously reported to influence digestibility: OsAT10; OsIRX9; and OsMYB58/63-L.ConclusionsDespite the difficulties associated with multi-phasic analysis of complex traits in novel germplasm, a moderate resolution GWAS successfully identified genetic associations encompassing both known and/or novel genes involved in determining the saccharification potential and lignin content of rice straw. Plausible candidates within QTL regions, in particular those with roles in cell wall biosynthesis, were identified but will require validation to confirm their value for application in rice breeding.

Production of cellulolytic enzymes by Myceliophthora thermophila and their applicability in saccharification of rice straw

Optimization of cellulase production by Myceliophthora thermophila BJTLRMDU3 was studied in solid state fermentation. Sequential use of Plackett-Burman and response surface methodology (RSM) resulted in the production of 98.81, 243.19, and 316.48 U/g dry moldy residue (DMR) of FPase, CMCase, and β-glucosidase, respectively. Statistical optimization has resulted in more than 4.0-fold increase in the production of cellulases. Optimization of saccharification of untreated and pretreated rice straw was carried out by cellulolytic enzymes of thermophilic mold M. thermophila. The liberation of reducing sugars was higher using fungal cellulases in ammonia-pretreated rice straw as compared with untreated biomass. Maximum liberation of reducing sugars was attained at 60 °C (224.24 mg/g substrate) and pH 5.0 (246.33 mg/g substrate) after an incubation time of 24 h (345.61 mg/g substrate) using enzyme dose of 20 U/g in ammonia-pretreated rice straw. Supplementation of xylanase further enhanced the saccharification (488.78 mg/g substrate) of pretreated rice straw. Analysis using high-performance liquid chromatography (HPLC) indicated the presence of various monomeric and oligomeric sugars in the enzymatic hydrolysate of pretreated rice straw. Both, Fourier-transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) revealed the structural changes in rice straw after ammonia pretreatment.

A low-cost approach for the generation of enhanced sugars and ethanol from rice straw using in-house produced cellulase-hemicellulase consortium from A. niger P-19

A natural variant of Aspergillus niger P-19 was used for the in-house production of cellulase-hemicellulase consortium for efficient and low-cost saccharification of rice straw. Solid-state fermentation of raw rice straw produced the highest enzyme titers corresponding to 126, 36, 47, 693, and 57 IU/g for CMCase, FPase, β-glucosidase, xylanase, and mannanase after 5 days. The enzyme characterization revealed that all the components of the consortium had the optima at 60 °C and pH 4.0 and were highly stable at 50-60 °C for up to 408 h. The crude in-house enzyme preparation worked well in the saccharification of 0.25 N NaOH pretreated rice straw releasing 70 g/l of reducing sugars with 10% solid loading thus proving to be a low-cost approach for producing high titers of sugars. The fermentation of C6 sugars resulted in an ethanol yield of 15.6 g/l with scope for improving the yield by simultaneously targeting the C5 sugars.

Significant boost in xylose yield and enhanced economic value with one-pot process using deep eutectic solvent for the pretreatment and saccharification of rice straw

The conversion of crop wastes into fermentable sugars and other chemicals mediated by deep eutectic solvents (DESs) has attracted significant attention. In this work, lactic acid, the constituents of DES, was proved to be a harmful inhibitor for cellulase during the conversion of rice straw to fermentable sugars. Nevertheless, the study here also demonstrated that depending on conditions, lactic acidic–choline chloride (LC) can be utilized for pretreatment and saccharification in a one-pot (PSOP) process with high sugar release. The PSOP process performed at 120℃ for 3 h, 15% biomass loading, a 0.30 mol/L LC with a 40 FPU enzymes saccharification system, achieved a total sugar yield of 75.7%. This value is significantly higher than the 49.9% yield achieved in traditional solid-liquid separation (SLS) processes due to the excellent xylose yield (75.7%). This high total sugar yield is attributed to the retention of the xylooligosaccharide, which was directly utilized in the PSOP process. In addition, the techno-economic analysis demonstrates the potential feasibility of a LC based PSOP process in industrial application.

Process development for sodium carbonate pretreatment and enzymatic saccharification of rice straw for bioethanol production

Optimization of pretreatment of rice straw was carried out with sodium carbonate. Initially, sodium carbonate pretreatment of rice straw followed by saccharification using partially purified cellulolytic enzymes of thermophilic mould Myceliophthora thermophila BJTLRMDU3 (20 U/g) at 60 °C and pH 5.0 after 6 h, released about 3-fold more reducing sugars with autoclaving (154.93 mg/g substrate) as compared to room temperature (51.01 mg/g substrate). Further optimization was carried out using statistical tools by response surface methodology (RSM) selecting three variables i.e., sodium carbonate concentration, substrate concentration and autoclaving time. Statistical optimization has resulted in enhanced liberation of reducing sugars i.e., 531.2 mg/g substrate using 5% rice straw, 1.25% sodium carbonate and autoclave time of 30 min after saccharification for 6 h. Furthermore, maximum liberation of reducing sugars (728.45 mg/g substrate) from pretreated rice straw was recorded after 48 h. Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM) data clearly confirmed the breakdown of cellulose and hemicellulose, removal of lignin and morphological changes in pretreated rice straw. Fermentation of enzymatic hydrolysate (20%) was carried out by Saccharomyces cerevisiae at 30 °C, pH 6.0, 150 rpm that resulted in 18.07 g/L ethanol after 72 h.