Enhanced the enzymatic hydrolysis efficiency of wheat straw after combined steam explosion and laccase pretreatment

Offsetting the environmental impacts of single or multi-product biorefineries from wheat straw

Moving toward a bioeconomy system is fundamental to climate change mitigation, nevertheless, the biotechnological routes should guarantee an environmental sustainability. Isobutene, a precursor in several industrial applications, is one of those chemicals that the environmental effects of its bio-based production have been scarcely explored. This study aims to assess the environmental performance of two biorefinery systems: the first one focuses only on the production of isobutene (I) and the second one on the co-production with lignin (I + L), both from the valorisation of wheat straw. The Life Cycle Assessment methodology is used to determine the environmental impacts considering mid-point and end-point categories. Biorefineries report 0.65 and 1.32 kg CO₂-eq per kg of biomass processed for I and I + L system, respectively. The most affected endpoint damage category corresponds to Human Health, regardless of the scenarios. Moreover, the pre-treatment stage constitutes the main hotspot of both systems considering midpoint and endpoint perspectives.

The Deconstruction of the Lignocellulolytic Structure of Sugarcane Bagasse by Laccases Improves the Production of H2 and Organic Acids

The production of biofuels using sugarcane bagasse (SCB) as substrate can be considered an environmentally friendly approach, due to the possibility of combining energy production with the reuse of agroindustrial wastes. This study was undertaken to explore the applicability of a new extract with the enzymes (Lac_mix) isolated from Chaetomium cupreum for SCB pretreatment. Lac_mix was more active at pH of 2.2 to 4 and 50 to 60 °C. Further, the individual and mutual effects of SCB concentration (6.6 to 23.4 g L^- 1), enzyme concentration (0.066 to 0.234 U L^- 1), and incubation time of the SCB with Lac_mix (19 to 221 min) on SCB pretreatment were evaluated using a response surface methodology and central composite design. The optimized conditions were 23.4 g L^- 1 SCB, 0.234 U mL^- 1 laccases, and 2.44 h resulting in 547 ± 108 mg L^- 1 of total sugars. This value agrees with the predicted value (455 ± 41 mg L^- 1) by the statistical model. Through the SCB pretreated with Lac_mix fermentation, 96.1% more H₂ and 22.5% more organic acids were observed compared to SCB without pretreatment. Therefore, laccases improve delignification, maximizing biomass fermentation for biofuel production.

Environmental assessment of the production of itaconic acid from wheat straw under a biorefinery approach

This study performs the environmental assessment of itaconic acid (IA) production from wheat straw. The Life Cycle Assessment (LCA) methodology is used to determine the environmental hotspots, considering impact categories such as Global Warming (GW), Fossil Resource Scarcity (FRS), Water Consumption (WC), among others. A sensitivity analysis was performed considering an optimization of the steam explosion process and 100% renewable energy. Results report an impact of about 14.33 kg CO₂ eq in GW, 4.15 kg of oil eq in FRS, for each kg of IA produced for the baseline scenario. Moreover, the pretreatment and fermentation stages constitute hotspots of the IA production. In addition, using a renewable energy source in production would reduce the impact by 82% in GW, 71% in PM and 82% in FRS categories. The optimization of the steam explosion process presents a better performance in GW and FRS but also lies in an increase in WC.

Enhancement of the enzymatic hydrolysis efficiency of wheat bran using the Bacillus strains and their consortium

In the downstream process, the bioconversion of lignocellulosic biomass can be improved by applying a biological pretreatment procedure using microorganisms to produce hydrolytic enzymes to modify the recalcitrant structure of lignocellulose. In this study, various Bacillus strains (B. subtilis B.01162 and B.01212, B. coagulans B.01123 and B.01139, B. cereus B.00076 and B.01718, B. licheniformis B.01223 and B.01231) were evaluated for the degrading capacity of wheat bran in the submerged medium using enzymatic activities, reducing sugars and weight loss as indicators. The obtained results revealed that the B. subtilis B.01162, B. coagulans B.01123 and B. cereus B.00076 could be promising degraders for the wheat bran pretreatment. Besides, the application of their consortium (the combination of 2-3 Bacillus species) showed the positive effects on cellulose bioconversion compared with monocultures. Among them, the mixture of B. subtilis B.01162 and B. coagulans B.01123 increased significantly the cellulase, endo-glucanase, and xylanase enzyme activity resulting in accelerating the lignocellulose degradation. Our results served a very good base for the development of microbial consortium for biological pretreatment of lignocellulosic raw materials.

Enhancement of Biological Pretreatment on Rice Straw by an Ionic Liquid or Surfactant

Fungal delignification can be a feasible process to pretreat biomass for bioethanol production if its performance is improved in terms of efficiency through a few modifications. The aim of this study was to enhance the biodelignification pretreatment of rice straw using laccase in the presence of ionic liquid (1-Allyl-3-methylimidazolium chloride, [AMIM]Cl) or surfactant (TritonX-100). Addition of 750 mg/L [AMIM]Cl and 500 mg/L TritonX-100 increases the lignin removal to 18.49% and 31.79%, which is higher than that of laccase only (11.97%). The enzymatic saccharification process was carried out based on different strategies. The highest cellulose conversion, 40.96%, 38.24%, and 37.91%, was obtained after 72 h of enzymatic saccharification when the substrate was washed with distilled water after pretreatment of rice straw with laccase + TritonX-100, laccase + [AMIM]Cl, and laccase only, respectively. In addition, the morphology and structure changes of pretreated and untreated rice straw were studied. Both surface area and cellulose crystallinity are substantially altered after laccase + [AMIM]Cl and laccase + TritonX-100 pretreatment. Enhanced saccharification efficiency of rice straw was achieved by laccase pretreatment with ionic liquid or surfactant in a single system.

Heterologous Expression of Laccase From Lentinula edodes in Pichia pastoris and Its Application in Degrading Rape Straw

Rape straw cannot be efficiently degraded and utilized by ruminants due to its severe lignification and complex cross-linked structure between fiber and lignin. The laccases can catalyze the inter-unit bond cleavage in lignin substrates. Therefore, this study investigated the recombinant laccase from Lentinula edodes (LeLac) and its application in degrading rape straw. The LeLac was expressed using Pichia pastoris. It had the maximum activity at 60°C and pH 3.0 using ABTS as substrate and at 50°C and pH 4.0 using o-tolidine as substrate. The LeLac exhibited preferential oxidation of ABTS and featured resistance to high temperature, but relatively poor thermal stability. The LeLac activity could be strengthened by Cu²⁺ in dose-dependent manners. The LeLac could tolerate 15% of ethanol and methanol. The optimal pH for the lignin degradation of rape straw acid detergent fiber (ADF) by LeLac was 4.0. The LeLac could improve the cellulose enzymolysis of rape straw ADF by degrading its lignin. Relatively fewer lignin but more soluble phenols from original rape straw were removed by LeLac. The enhancement of enzymatic hydrolysis in original rape straw should be a combined result of polyphenols removal and lignin degradation caused by LeLac. This study demonstrated that the LeLac could improve the utilization of rape straw by degrading its lignin, meanwhile it’s worth noting that removing the soluble phenols by LeLac might also play an important role.

Enhanced Enzymatic Hydrolysis and Lignin Extraction of Wheat Straw by Triethylbenzyl Ammonium Chloride/Lactic Acid-Based Deep Eutectic Solvent Pretreatment

Efficient and feasible pretreatment of lignocellulosic biomass waste is an important prerequisite step to promote subsequent enzymatic hydrolysis and enhance the economics of biofuels production. This study focuses on the pretreatment of wheat straw (WS) with triethylbenzyl ammonium chloride/lactic acid (TEBAC/LA)-based deep eutectic solvents to enhance biomass fractionation and lignin extraction. Effects of pretreatment time, temperature, and TEBAC/LA molar ratio on pretreatment were evaluated systematically. Results suggested that 89.06 ± 1.05% of cellulose and 71.00 ± 1.03% of xylan were hydrolyzed with enzyme loadings of 35 FPU cellulase and 82 CBU β-glucosidase (per gram of dry biomass) after pretreatment by TEBAC/LA (1:9) at 373 K for 10 h. A total monosaccharide yield of 0.550 g/g WS (91.27% of the theoretical yield) was achieved with 79.73 ± 0.93% of lignin removal. Furthermore, the ¹H-¹³C two-dimensional heteronuclear single quantum correlation (2D-HSQC) NMR spectroscopy showed that the regenerated lignin (75.69 ± 1.32% purity) was mainly composed of the syringyl units and the guaiacyl units. Overall, the results in this study provide an effective and facile pretreatment method for lignocellulosic biomass waste to enhance enzymatic hydrolysis saccharification.

Effect of Novel Pretreatment of Steam Explosion Associated with Ammonium Sulfite Process on Enzymatic Hydrolysis of Corn Straw

Effective pretreatment process to improve enzymatic saccharification and decrease inhibitors generation is a key operation involved in the lignocellulosic bioconversion. The pretreatment of steam explosion associated with ammonium sulfite (SEAS) process was carried out to investigate the effect on enzymatic hydrolysis and fermentation production as a combinatorial pretreatment. Results showed that after pretreatment (1.0 MPa, 30 min, 20%w/w ammonium sulfite added), the phenolic inhibitors derived from lignin significantly removed (37.8%), which transformed to chemical humic acid (humic acid and fulvic acid) mostly. Sugar conversion (glucan (77.8%) and xylan (73.3%)) and ethanol concentration (40.8 g/L) of combinatorial pretreated samples were increased by 24.7% and 33.8%, respectively, compared with steam explosion (SE) pretreated samples. FT-IR and elemental analysis results indicated that the lignin structure changed and aromatization degree increased after SEAS pretreatment. In addition, the ratio of C/N decreased and compost maturity degree increased with the holding time. The effect on the growth of wheat seedlings of soluble fulvic acid solution from combinatorial pretreatment was investigated, where below 1% (w/w) concentration did contribute to growth. Therefore, one-step chemical pretreatment process could be provided for inhibitors removal, enzymatic saccharification increase, and chemical humic acid formation as well.

Pretreatment of wheat straw using basic ethanolamine-based deep eutectic solvents for improving enzymatic hydrolysis

A series of ethanolamine based deep eutectic solvents (DESs), which have strong basicity, were firstly applied in wheat straw pretreatment. Typically, choline chloride: monoethanolamine (C:M) as the best solvent among these DESs can remove 71.4% lignin and reserve 93.7% cellulose (70 °C, L/S mass ratio of 20:1, 9 h), and improve the enzymatic hydrolysis of residue, i.e., 89.8% cellulose and 62.0% xylan conversion. The pretreatment capacity of C:M is comparable to other solvents while C:M has several advantages, e.g., lower cost with cheap materials and simpler preparation process, mild conditions and lower polysaccharide loss. The XRD, SEM and FT-IR results verified that the polysaccharide conversion and sugars yield were enhanced by the removal of lignin in the pretreatment process. The basic ethanolamine based DESs are promising solvents for industrial application of wheat straw pretreatment.

Heterologous expression of a Streptomyces cyaneus laccase for biomass modification applications

Laccases are used for the conversion of biomass into fermentable sugars but it is difficult to produce high yields of active laccases in heterologous expression systems. We overcame this challenge by expressing Streptomyces cyaneus CECT 3335 laccase in Escherichia coli (ScLac) and we achieved a yield of up to 104 mg L-1 following purification by one-step affinity chromatography. Stability and activity assays using simple lignin model substrates showed that the purified enzyme preparation was active over a broad pH range and at high temperatures, suggesting it would be suitable for biomass degradation. The reusability of ScLac was also demonstrated by immobilizing the enzyme on agarose beads with a binding yield of 33%, and by the synthesis of cross-linked enzyme aggregates with an initial activity recovery of 72%.

Cholinium amino acids-glycerol mixtures: New class of solvents for pretreating wheat straw to facilitate enzymatic hydrolysis

New solvents for pretreating wheat straw, mixtures of cholinium amino acids ionic liquids ([Ch][AA] ILs) and glycerol, were developed. As a typical result, 50% cholinium alanine-glycerol is capable of removing 67.6% lignin while reserving 95.1% cellulose (90°C, L/S mass ratio of 20:1, 6h) and the conversions of cellulose and xylan are 89.7% and 70.9%, respectively, which is comparable to the pretreatment capability of other solvents, while [Ch][AA]-glycerol mixtures have desirable advantages, e.g., biocompatibility, lower cost with adding glycerol than pure IL, much lower pretreatment temperature (typically <100°C) than that by glycerol (typically >200°C). Lignin removal and polysaccharide conversion are dependent on [Ch][AA] content and pH of pretreatment solvents. [Ch][AA] not only remove lignin in wheat straw effectively but also swell cellulose while not remarkably dissolve cellulose with high cellulose reservation, favoring the enzymatic hydrolysis. Such mixtures of ILs and co-solvents are potential solvents for pretreating biomass.

Development of natural cellulase inhibitor mediated intensified biological pretreatment technology using Pleurotus florida for maximum recovery of cellulose from paddy straw under solid state condition

Inhibitor mediated intensified bio-pretreatment (IMBP) technology using natural cellulase inhibitor (NCI) for maximum cellulose recovery from paddy straw was studied. Pretreatment was carried out under solid state condition. Supplementation of 8% NCI in pretreatment medium improves cellulose recovery and delignification by 1.2 and 1.5-fold respectively, compared to conventional bio-pretreatment due to inhibition of 61% of cellulase activity in IMBP. Further increase in NCI concentration showed negative effect on Pleurotus florida growth and suppress the laccase productivity by 1.1-fold. Laccase activity in IMBP was found to be 2.0U/mL on 19^thday, which is higher than (1.5U/mL) conventional bio-pretreatment. Physico-chemical modifications in paddy straw before and after pretreatment were analysed by SEM, ATR-FTIR, XRD and TGA. According to these findings, the IMBP technology can be a viable eco-friendly technology for sustainable production of bioethanol with maximum cellulose recovery.

Steam explosion distinctively enhances biomass enzymatic saccharification of cotton stalks by largely reducing cellulose polymerization degree in G. barbadense and G. hirsutum

In this study, steam explosion pretreatment was performed in cotton stalks, leading to 5-6 folds enhancements on biomass enzymatic saccharification distinctive in Gossypium barbadense and Gossypium hirsutum species. Sequential 1% H2SO4 pretreatment could further increase biomass digestibility of the steam-exploded stalks, and also cause the highest sugar-ethanol conversion rates probably by releasing less inhibitor to yeast fermentation. By comparison, extremely high concentration alkali (16% NaOH) pretreatment with raw stalks resulted in the highest hexoses yields, but it had the lowest sugar-ethanol conversion rates. Characterization of wall polymer features indicated that biomass saccharification was enhanced with steam explosion by largely reducing cellulose DP and extracting hemicelluloses. It also showed that cellulose crystallinity and arabinose substitution degree of xylans were the major factors on biomass digestibility in cotton stalks. Hence, this study has provided the insights into cell wall modification and biomass process technology in cotton stalks and beyond.

Unraveling the effects of laccase treatment on enzymatic hydrolysis of steam-exploded wheat straw

Laccase enzymes are promising detoxifying agents during lignocellulosic bioethanol production from wheat straw. However, they affect the enzymatic hydrolysis of this material by lowering the glucose recovery yields. This work aimed at explaining the negative effects of laccase on enzymatic hydrolysis. Relative glucose recovery in presence of laccase (10IU/g substrate) with model cellulosic substrate (Sigmacell) at 10% (w/v) was almost 10% points lower (P<0.01) than in the absence of laccase. This fact could be due to an increase in the competition of cellulose binding sites between the enzymes and a slight inhibition of β-glucosidase activity. However, enzymatic hydrolysis and infrared spectra of laccase-treated and untreated wheat straw filtered pretreated residue (WS-FPR), revealed that a grafting process of phenoxy radicals onto the lignin fiber could be the cause of diminished accessibility of cellulases to cellulose in pretreated wheat straw.

De-ashing treatment of corn stover improves the efficiencies of enzymatic hydrolysis and consequent ethanol fermentation

In this study, corn stover with different ash content was pretreated using dry dilute acid pretreatment method at high solids loading of 67% (w/w). The results indicate that the hydrolysis yield of corn stover is increased from 43.30% to 70.99%, and ethanol yield is increased from 51.74% to 73.52% when ash is removed from 9.60% to 4.98%. The pH measurement of corn stover slurry indicates that the decrease of pretreatment efficiency is due to the neutralization of sulfuric acid by alkaline compounds in the ash. The elemental analysis reveals that the ash has the similar composition with the farmland soil. This study demonstrates the importance of ash removal from lignocellulose feedstock under high solids content pretreatment.

Enhanced fermentability of poplar by combination of alkaline peroxide pretreatment and semi-simultaneous saccharification and fermentation

To improve ethanol productivity with few inhibitors generated, a novel process of combined alkaline peroxide (AP) pretreatment and semi-simultaneous saccharification and fermentation (SSSF) was developed in this work. Pretreatment with 10% (g H2O2/g wood) H2O2 at 160°C for 2h followed by SSSF was found to be the optimal combination with remarkably increased ethanol yield. The proposed process resulted in 63.1% of ethanol yield, which was about five times more than that of the untreated sample that was processed using conventional simultaneous saccharification and fermentation (SSF). The efficient conversion was ascribed to the high delignification efficiency (64.9%) of AP pretreatment, which led to incompact structure and generation of fewer inhibitors during SSSF (c. 6g/L of lactic acid) than SSF (c. 10 g/L of lactic acid). This combined approach was proved to be an effective method for the promotion of the bioconversion of lignocellulosic materials.

Novel method utilizing microbial treatment for cleaner production of diosgenin from Dioscorea zingiberensis C.H. Wright (DZW)

A novel method utilizing microbial treatment for cleaner production of diosgenin from Dioscorea zingiberensis C.H. Wright (DZW) was presented. A new Bacillus pumilus HR19, which has the great ability to secrete pectinase, was screened and applied in the microbial treatment. Low-pressure steam expansion pretreatment (LSEP) was employed in advance to assist microbial treatment efficiently in releasing saponins, which are the precursors of diosgenin. Compared with the traditional process of acid hydrolysis, this novel process reduced the consumptions of water, acid and organic solvent by more than 92.5%, 97.0%, 97.0%, respectively, while simultaneously increasing the diosgenin yield by 6.21%. In addition, the microbial treatment was more efficient than enzymatic treatment, which arised from that microorganisms could be induced to secrete related enzymes by the compositions of DZW and relieve product inhibition by utilizing enzyme hydrolysates.

Biobutanol from sweet sorghum bagasse hydrolysate by a hybrid pervaporation process

In this study, the pervaporation membrane was used not only for the detoxification of sweet sorghum bagasse (SSB) hydrolysate, but also for butanol separation from its fermentation broth. As a result of detoxification, about 94.5% furfural was reduced by the pervaporation method, and 138.25 g/L furfural was obtained in the permeate side. 87.5% phenolic compounds were degradated by further laccase detoxification. As for fermentation part, 12.3±0.1 g/L butanol, 6.1±0.05 g/L acetone and 2.5±0.07 g/L ethanol were obtained. And after 2h of pervaporation separation, 201.9 g/L butanol, 76.2g/L acetone and traces of ethanol were obtained in the permeate. The hybrid pervaporation process shows promising for the industrial production of biofuel butanol and biochemical furfural.

Biological pretreatment of corn stover with ligninolytic enzyme for high efficient enzymatic hydrolysis

Aiming at increasing the efficiency of transferring corn stover into sugars, a biological pretreatment was developed and investigated in this study. The protocol was characterized by the pretreatment with crude ligninolytic enzymes from Phanerochete chrysosporium and Coridus versicolor to break the lignin structure in corn stover, followed by a washing procedure to eliminate the inhibition of ligninolytic enzyme on cellulase. By a 2 d-pretreatment, sugar yield from corn stover hydrolysis could be increased by 50.2% (up to 323 mg/g) compared with that of the control. X-ray diffractometry and FT-IR analysis revealed that biological pretreatment could partially remove the lignin of corn stover, and consequently enhance the enzymatic hydrolysis efficiency of cellulose and hemeicellulose. In addition, the amount of microbial inhibitors, such as acetic acid and furfural, were much lower in biological pretreatment than that in acid pretreatment. This study provided a promising pretreatment method for biotransformation of corn stovers.

Evaluation of ligninolytic enzymes, ultrasonication and liquid hot water as pretreatments for bioethanol production from cotton gin trash

Cotton gin trash (CGT) is a ubiquitous cotton-production-waste resource which can be used for ethanol production. In this research, seven combinations of three pretreatments; ultrasonication, liquid hot water and ligninolytic enzymes were evaluated on CGT to select the best pretreatments combination that increased the cellulose conversion and the ethanol yield in the saccharification and fermentation processes, respectively. The structural changes in the cellulose, hemicellulose and lignin from CGT were followed using FT-IR after each pretreatment. All the pretreatment combinations modified the CGT's structure and composition compared with the unpretreated CGT, and the majority of them improved release of sugars originally present in the CGT. The best results were achieved by the sequential combination of ultrasonication, hot water, and ligninolytic enzymes with an improvement of 10% in the ethanol yield and cellulose conversion compared to the other pretreatments. These results are a contribution to develop a feasible bioethanol production from CGT.