Structural changes of lignocelluloses by a nonionic surfactant, Tween 20, and their effects on cellulase adsorption and saccharification

Development of a DC-Biased AC-Stimulated Microfluidic Device for the Electrokinetic Separation of Bacterial and Yeast Cells

Electrokinetic (EK) microsystems, which are capable of performing separations without the need for labeling analytes, are a rapidly growing area in microfluidics. The present work demonstrated three distinct binary microbial separations, computationally modeled and experimentally performed, in an insulator-based EK (iEK) system stimulated by DC-biased AC potentials. The separations had an increasing order of difficulty. First, a separation between cells of two distinct domains (Escherichia coli and Saccharomyces cerevisiae) was demonstrated. The second separation was for cells from the same domain but different species (Bacillus subtilis and Bacillus cereus). The last separation included cells from two closely related microbial strains of the same domain and the same species (two distinct S. cerevisiae strains). For each separation, a novel computational model, employing a continuous spatial and temporal function for predicting the particle velocity, was used to predict the retention time (tR,p) of each cell type, which aided the experimentation. All three cases resulted in separation resolution values Rs>1.5, indicating complete separation between the two cell species, with good reproducibility between the experimental repetitions (deviations < 6%) and good agreement (deviations < 18%) between the predicted tR,p and experimental (tR,e) retention time values. This study demonstrated the potential of DC-biased AC iEK systems for performing challenging microbial separations.

Advances and perspectives on mass transfer and enzymatic hydrolysis in the enzyme-mediated lignocellulosic biorefinery: A review

Enzymatic hydrolysis is a critical process for the cellulase-mediated lignocellulosic biorefinery to produce sugar syrups that can be converted into a whole range of biofuels and biochemicals. Such a process operating at high-solid loadings (i.e., scarcely any free water or roughly ≥ 15% solids, w/w) is considered more economically feasible, as it can generate a high sugar concentration at low operation and capital costs. However, this approach remains restricted and incurs "high-solid effects", ultimately causing the lower hydrolysis yields with increasing solid loadings. The lack of available water leads to a highly viscous system with impaired mixing that exhibits strong transfer resistance and reaction limitation imposed on enzyme action. Evidently, high-solid enzymatic hydrolysis involves multi-scale mass transfer and multi-phase enzyme reaction, and thus requires a synergistic perspective of transfer and biotransformation to assess the interactions among water, biomass components, and cellulase enzymes. Porous particle characteristics of biomass and its interface properties determine the water form and distribution state surrounding the particles, which are summarized in this review aiming to identify the water-driven multi-scale/multi-phase bioprocesses. Further aided by the cognition of rheological behavior of biomass slurry, solute transfer theories, and enzyme kinetics, the coupling effects of flow-transfer-reaction are revealed under high-solid conditions. Based on the above basic features, this review lucidly explains the causes of high-solid hydrolysis hindrances, highlights the mismatched issues between transfer and reaction, and more importantly, presents the advanced strategies for transfer and reaction enhancements from the viewpoint of process optimization, reactor design, as well as enzyme/auxiliary additive customization.

Non-ionic surfactant formulation sequentially enhances the enzymatic hydrolysis of cellulignin from sugarcane bagasse and the production of Monascus ruber biopigments

The effect of a non-ionic surfactant optimized formulation (SOF) obtained from an experimental design was evaluated for different influencing variables in the processing of sugarcane bagasse cellulignin to produce biopigments. The major findings in the saccharification stage using the SOF point that: at same enzyme loading, the highest glucan hydrolysis yield was 63 % (2-fold higher compared to control); the enzyme loading of 2.5 FPU/g resulted in similar yield compared to 10 FPU/g (control); 15 % (m/v) of total solids loading maintained the yield in fed-batch configuration; the hydrolysis yield is maintained at high shear force stress (800 rpm of stirring rate) and temperatures (50-70 °C). Besides, under separate and semi-simultaneous hydrolysis and fermentation, the maximum biopigments production were of 10 AU_510nm/mL and 17.84 AU_510nm/mL, respectively. The SOF used in this study was found to be a promising additive either in a single or sequential steps to produce biopigments in biorefineries.

Roles of Surfactants in Oriented Immobilization of Cellulase on Nanocarriers and Multiphase Hydrolysis System

Surfactants, especially non-ionic surfactants, play an important role in the preparation of nanocarriers and can also promote the enzymatic hydrolysis of lignocellulose. A broad overview of the current status of surfactants on the immobilization of cellulase is provided in this review. In addition, the restricting factors in cellulase immobilization in the complex multiphase hydrolysis system are discussed, including the carrier structure characteristics, solid-solid contact obstacles, external diffusion resistance, limited recycling frequency, and nonproductive combination of enzyme active centers. Furthermore, promising prospects of cellulase-oriented immobilization are proposed, including the hydrophilic-hydrophobic interaction of surfactants and cellulase in the oil-water reaction system, the reversed micelle system of surfactants, and the possible oriented immobilization mechanism.

High solid loading enzymatic hydrolysis of acetic acid-peroxide/acetic acid pretreated poplar and cellulase recycling

High solid loading saccharification is the premise of preparing high-concentration sugar which is beneficial to bioethanol production, but the limited sugar concentration and high enzyme dosage are two challenges. In this work, the glucan-rich acetic acid-hydrogen peroxide/acetic acid (AC-HPAC)-pretreated poplar (85.8%) were prepared for enzymatic hydrolysis at 10%-40% solid loading and the strategies for reducing cellulase dosage were explored. Results showed that the maximum glucose concentration reached to 250.8 g/L at 40% solid loading, which was the highest concentration in previous literatures. As the solid loading was 20%, the addition of Tween 80 saved 50% of cellulase and the recycling of unhydrolyzed residue (0.2 g/g DM) saved another 25% of cellulase, resulting in 152.2 g/L of glucose concentration with yield of 79.9%. This work showed potential of poplar to produce the high concentration glucose solution with low enzyme loading through the recycling of enzyme bound onto unhydrolyzed residue.

Interplays of enzyme, substrate, and surfactant on hydrolysis of native lignocellulosic biomass

Tracking enzyme, substrate, and surfactant interactions to reach maximum reducing sugar production during enzymatic hydrolysis of plant biomass may provide a better understanding of factors that limit the lignocellulosic material degradation in native rice straw. In this study, enzymes (Cellic Ctec2 cellulase and Cellic Htec2 xylanase) and Triton X-100 (surfactant) were used as biocatalysts for cellulose and xylan degradation and as a lignin blocking agent, respectively. The response surface model (R² = 0.99 and R²-adj = 0.97) indicated that Cellic Ctec2 cellulase (p < 0.0001) had significant impacts on reducing sugar production, whereas Cellic Htec2 xylanase and Triton X-100 had insignificant impacts on sugar yield. Although FTIR analysis suggested binding of Triton X-100 to lignin surfaces, the morphological observation by SEM revealed similar surface features (i.e., smooth surfaces with some pores) of rice straw irrespective of Triton X-100. The reducing sugar yields from substrate hydrolysis with or without the surfactant were comparable, suggesting similar exposure of polysaccharides accessible to the enzymes. The model analysis and chemical and structural evidence suggest that there would be no positive effects on enzymatic hydrolysis by blocking lignins with Triton X-100 if high lignin coverage exists in the substrate due to the limited availability of hydrolyzable polysaccharides.

Erythrocyte haemotoxicity profiling of snake venom toxins after nanofractionation

Snakebite is classified as a priority Neglected Tropical Disease by the World Health Organization. Understanding the pathology of individual snake venom toxins is of great importance when developing more effective snakebite therapies. Snake venoms may induce a range of pathologies, including haemolytic activity. Although snake venom-induced erythrocyte lysis is not the primary cause of mortality, haemolytic activity can greatly debilitate victims and contributes to systemic haemotoxicity. Current assays designed for studying haemolytic activity are not suitable for rapid screening of large numbers of toxic compounds. Consequently, in this study, a high-throughput haemolytic assay was developed that allows profiling of erythrocyte lysis, and was validated using venom from a number of medically important snake species (Calloselasma rhodostoma, Daboia russelii, Naja mossambica, Naja nigricollis and Naja pallida). The assay was developed in a format enabling direct integration into nanofractionation analytics, which involves liquid chromatographic separation of venom followed by high-resolution fractionation and subsequent bioassaying (and optional proteomics analysis), and parallel mass spectrometric detection. Analysis of the five snake venoms via this nanofractionation approach involving haemolytic assaying provided venom-cytotoxicity profiles and enabled identification of the toxins responsible for haemolytic activity. Our results show that the elapid snake venoms (Naja spp.) contained both direct and indirect lytic toxins, while the viperid venoms (C. rhodostoma and D. russelii) only showed indirect lytic activities, which required the addition of phospholipids to exert cytotoxicity on erythrocytes. The haemolytic venom toxins identified were mainly phospholipase A2s and cytotoxic three finger toxins. Finally, the applicability of this new analytical method was demonstrated using a conventional snakebite antivenom treatment and a small-molecule drug candidate to assess neutralisation of venom cytotoxins.

Catalytic Performance of a Recombinant Organophosphate-Hydrolyzing Phosphotriesterase from Brevundimonas diminuta in the Presence of Surfactants

Phosphotriestease (PTE), also known as parathion hydrolase, has the ability to hydrolyze the triester linkage of organophosphate (OP) pesticides and chemical warfare nerve agents, making it highly suitable for environment remediation. Here, we studied the effects of various surfactants and commercial detergents on the esterase activity of a recombinant PTE (His6-tagged BdPTE) from Brevundimonas diminuta. Enzymatic assays indicated that His6-tagged BdPTE was severely inactivated by SDS even at lower concentrations and, conversely, the other three surfactants (Triton X-100, Tween 20, and Tween 80) had a stimulatory effect on the activity, especially at a pre-incubating temperature of 40 °C. The enzyme exhibited a good compatibility with several commercial detergents, such as Dr. Formula® and Sugar Bubble®. The evolution results of pyrene fluorescence spectroscopy showed that the enzyme molecules participated in the formation of SDS micelles but did not alter the property of SDS micelles above the critical micelle concentration (CMC). Structural analyses revealed a significant change in the enzyme’s secondary structure in the presence of SDS. Through the use of the intentionally fenthion-contaminated Chinese cabbage leaves as the model experiment, enzyme–Joy® washer solution could remove the pesticide from the contaminated sample more efficiently than detergent alone. Overall, our data promote a better understanding of the links between the esterase activity of His6-tagged BdPTE and surfactants, and they offer valuable information about its potential applications in liquid detergent formulations.

Natural surfactant-aided dilute sulfuric acid pretreatment of waste wheat straw to enhance enzymatic hydrolysis efficiency

Traditional surfactants have been reported to enhance enzymatic saccharification of lignocellulose, however, it is important to transfer these findings to a system that uses a high-efficiency and low-toxicity natural surfactant instead. In this work, a novel hybrid method involving use of the natural surfactant (humic acid, HA) during mild acid (H₂SO₄) pretreatment was developed for waste wheat straw (WWS) biorefinery. The HA was found to help remove lignin up to 40.6%, and hemicellulose up to 96.2%. As a result of these changes, the enzymatic hydrolysis efficiency reached as high as 92.9%. The success of enzymatic digestion was partly attributed to the improved accessibility of cellulose to cellulase and changes in lignocellulose structures. We anticipate that these findings will be used to further evaluate HA as a beneficial surfactant in biorefinery pretreatment processes, and perhaps spur others to identify other natural surfactants that may prove even more effective.

Effect of the isoelectric point of pH-responsive lignin-based amphoteric surfactant on the enzymatic hydrolysis of lignocellulose

The isoelectric point (pI) of lignin-based surfactant is an important factor in the enhancement on the enzymatic hydrolysis of lignocellulose. In this work, lignin carboxylate (LC) and quaternary ammonium lignin carboxylates (LCQ-x, x%: the mass ratio of quaternizing agent to enzymatic hydrolysis lignin) with different isoelectric points were synthesized. LC or LCQ-x with pI significantly lower or higher than 4.8 reduced the non-productive adsorption of cellulase on lignin, but for the significant inhibitory effect on cellulase activity, their enhancements on the enzymatic hydrolysis of lignocellulose were not remarkable. However, LCQ-x with pI around 4.8 preserved the cellulase activity, and significantly reduced the non-productive adsorption of cellulase, therefore remarkably enhanced the enzymatic hydrolysis. 2 g/L LC, LCQ-40 (pI = 5.0) and LCQ-100 (pI = 9.2) increased the enzymatic digestibility of pretreated eucalyptus from 35.2% to 53.4%, 95.3% and 60.4% respectively. In addition, for the excellent pH-response performance, LCQ could be efficiently recovered after enzymatic saccharification.

Synergistic effects of surfactant-assisted biodegradation of wheat straw and production of polysaccharides by Inonotus obliquus under submerged fermentation

Current work proposes an innovative wheat straw biomass utilization strategy that connects efficient lignocellulose biodegradation with exo-polysaccharide (EPS) production in I. obliquus under submerged fermentation. The addition of Tween 80 increased the activities of ligninolytic enzymes MnP, LiP and Lac by 1200%, 125% and 39.9%, respectively. When wheat straw lignin recalcitrance was substantially reduced with the aid of Tween 80, I. obliquus was capable of utilizing the substrates and in turn accumulated EPS. The degradation of cellulose, hemicellulose and lignin reached 46.1%, 46.4% and 44.1% on Day 9 of growth, respectively. Meanwhile, the maximum mycelial biomass and EPS production increased by 23.3% and 142.9%, respectively. The EPS had higher contents of sugar, protein, uronic acid, and mannose ratio, and higher antioxidant activity against 2, 2-diphenyl-1-picrylhydrazyl (DPPH), 2,2-azinobis-(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS^•+) and hydroxyl radicals.

Dissecting the effect of polyethylene glycol on the enzymatic hydrolysis of diverse lignocellulose

Natural lignocellulose is used as raw material to produce chemicals through biological transformation. The accessibility of cellulase to substrate was also one of the limiting factors of industrial production. Polyethylene glycol (PEG) can be used as additive in enzymatic hydrolysis of lignocellulose. In this study, enzymatic activity on simultaneous or non-simultaneous addition of PEG 4000 was investigated, and the partly delignified rice straw, the rice straw and filter paper were used as substrates, respectively. Enzyme activity was characterized by reducing sugar concentration in supernatant which was quantified through 3,5-dinitrosalicylic acid (DNS) method. Addition of PEG has been proven to facilitate enzymatic hydrolysis of lignocellulosic materials. Furthermore, PEG had the positive effect on hydrolytic enzyme activity of pure cellulose materials without lignin. Changes in lignocellulose materials have been observed by inverted microscope and Scanning electron microscope (SEM), and no chemical changes were shown by Fourier transform infrared spectroscopy (FTIR). The promotion of PEG on enzymatic hydrolysis of pure cellulose materials may be due to its loose physical structure and similar phenomenon in natural lignin materials. PEG loosens the physical structure of lignocellulose, thus facilitating enzymatic hydrolysis. This may be a new idea to optimize the lignocellulosic enzymatic hydrolysis process.

Enhancement of bioethanol production from Moso bamboo pretreated with biodiesel crude glycerol: Substrate digestibility, cellulase absorption and fermentability

Utilization of sustainable energy is limited by energy requirement for the manufacturing of renewable fuels. Moso bamboo was pretreated with industrially derived crude glycerol obtained from different sources at 150/160 °C for 3 h. This bamboo, pretreated with base biodiesel glycerol with pressure filtration removal method, showed a high glucose yield of 94.95% and an ethanol yield of 73.10% of the theoretical. Major glycerol content was removed by pressure filtration, leaving a small amount of fatty acid soap in the pretreated sample, which formed an emulsion that reduced lignin redisposition onto the biomass surface and effectively blocked lignin absorption of cellulase, allowing greater enzymatic hydrolysis and fermentation system function. The surface was more hydrophilic and a higher lignin removal was achieved: 39.24% with base biodiesel glycerol pretreatment compared to 26.08% with sodium hydroxide glycerol pretreatment. This study provides a useful and cost-effective process, BBGP, for high-yield ethanol production.

Critical Point Drying: An Effective Drying Method for Direct Measurement of the Surface Area of a Pretreated Cellulosic Biomass

The surface area and pore size distribution of Eucalyptus samples that were pretreated by different methods were determined by the Brunauer–Emmett–Teller (BET) technique. Three methods were applied to prepare cellulosic biomass samples for the BET measurements, air, freeze, and critical point drying (CPD). The air and freeze drying caused a severe collapse of the biomass pore structures, but the CPD effectively preserved the biomass morphology. The surface area of the CPD prepared Eucalyptus samples were determined to be 58–161 m²/g, whereas the air and freeze dried samples were 0.5–1.3 and 1.0–2.4 m²/g, respectively. The average pore diameter of the CPD prepared Eucalyptus samples were 61–70 Å. The CPD preserved the Eucalyptus sample morphology by replacing water with a non-polar solvent, CO₂ fluid, which prevented hydrogen bond reformation in the cellulose.

Enhancing enzyme-aided production of fermentable sugars from poplar pulp in the presence of non-ionic surfactants

Addition of surfactants to enzymatic hydrolysis has been reported to enhance the hydrolytic potential of enzymes in the bioconversion of lignocellulosic biomass to fermentable sugars. The objective of this investigation was to evaluate the effects of four non-ionic surfactants (PEG4000, PEG8000, TitronX-100, and Tween80) on the efficiency of enzymatic hydrolysis of steam-pretreated poplar using a commercial cellulase preparation (Cellic® CTec2). Statistical discriminant analysis at four variable factors (surfactant type, surfactant concentration, hydrolysis time, and substrate consistency) revealed that enzymatic hydrolysis was significantly enhanced in the presence of PEG4000, with 19.2% increase in glucose yield over control without surfactant, whereas ANOVA test indicated substrate consistency and hydrolysis time as the most significant factors (P < 0.05). Hydrolysis of poplar pulp at 5% w/w pulp consistency with CTec2 in presence of 1% w/w PEG4000 produced the highest glucose yield of 58.5% after 96 h reaction time.

Nonionic surfactants enhanced enzymatic hydrolysis of cellulose by reducing cellulase deactivation caused by shear force and air-liquid interface

Effects of nonionic surfactants on enzymatic hydrolysis of Avicel at different agitation rates and solid loadings and the mechanism were studied. Nonionic surfactants couldn't improve the enzymatic hydrolysis efficiency at 0 and 100rpm but could enhance the enzymatic hydrolysis significantly at high agitation rate (200 and 250rpm). Cellulase was easily deactivated at high agitation rate and the addition of nonionic surfactants can protect against the shear-induced deactivation, especially when the cellulase concentration was low. When 25mg protein/L of cellulase solution was incubated at 200rpm for 72h, the enzyme activity increased from 36.0% to 89.5% by adding PEG4600. Moreover nonionic surfactants can compete with enzyme in air-liquid interface and reduce the amount of enzyme exposed in the air-liquid interface. The mechanism was proposed that nonionic surfactants could enhance the enzymatic hydrolysis of Avicel by reducing the cellulase deactivation caused by shear force and air-liquid interface.

Real-time adsorption and action of expansin on cellulose

BACKGROUND

Biological pretreatment is an environmentally safe method for disrupting recalcitrant structures of lignocellulose and thereby improving their hydrolysis efficiency. Expansin and expansin-like proteins act synergistically with cellulases during hydrolysis. A systematic analysis of the adsorption behavior and mechanism of action of expansin family proteins can provide a basis for the development of highly efficient pretreatment methods for cellulosic substrates using expansins.

RESULTS

Adsorption of Bacillus subtilis expansin (BsEXLX1) onto cellulose film under different conditions was monitored in real time using a quartz crystal microbalance with dissipation. A model was established to describe the adsorption of BsEXLX1 onto the film. High temperatures increased the initial adsorption rate while reducing the maximum amount of BsEXLX1 adsorbed onto the cellulose. Non-ionic surfactants (polyethylene glycol 4000 and Tween 80) at low concentrations enhanced BsEXLX1 adsorption; whereas, high concentrations had the opposite effect. However, sodium dodecyl sulfate inhibited adsorption at both low and high concentrations. We also investigated the structural changes of cellulose upon BsEXLX1 adsorption and found that BsEXLX1 adsorption decreased the crystallinity index, disrupted hydrogen bonding, and increased the surface area of cellulose, indicating greater accessibility of the substrate to the protein.

CONCLUSIONS

These results increase our understanding of the interaction between expansin and cellulose, and provide evidence for expansin treatment as a promising strategy to enhance enzymatic hydrolysis of lignocellulose.

Enhanced enzymatic hydrolysis of eucalyptus by synergy of zinc chloride hydrate pretreatment and bovine serum albumin

Enhancement of eucalyptus enzymatic saccharification by synergy of ZnCl₂ hydrate pretreatment and bovine serum albumin (BSA) was investigated in this study. The result showed that the ZnCl₂ hydrate pretreatment could not only selectively extract up to ∼100% of the hemicellulose from eucalyptus, but also convert portion of high crystalline cellulose I into low crystalline cellulose II, which both beneficial for enhancing subsequent pretreated solids enzymatic saccharification. The addition of BSA into enzymatic hydrolysis step could significantly promote the glucose release from pretreated solids, especially, under the low enzyme loading. Furthermore, the material balance indicated that the highest glucose yield of this study was 35.5g/100g raw material, which representing 90.3% of glucose in raw eucalyptus, combined with the xylose yield, 13.9g/100g eucalyptus, it can be concluded that ZnCl₂ hydrate pretreatment offered the potential to co-produce xylose and glucose from eucalyptus.

Additives enhancing enzymatic hydrolysis of lignocellulosic biomass

Linked to the development of cellulolytic enzyme cocktails from Myceliophthora thermophila, we studied the effect of different additives on the enzymatic hydrolysis yield. The hydrolysis of pretreated corn stover (PCS), sugar cane straw (PSCS) and microcrystalline cellulose (Avicel) was performed under industrial conditions using high solid loadings, limited mixing, and low enzyme dosages. The addition of polyethylene glycol (PEG4000) allowed to increase the glucose yields by 10%, 7.5%, and 32%, respectively in the three materials. PEG4000 did not have significant effect on the stability of the main individual enzymes but increased beta-glucosidase and endoglucanase activity by 20% and 60% respectively. Moreover, the presence of PEG4000 accelerated cellulase-catalyzed hydrolysis reducing up to 25% the liquefaction time. However, a preliminary economical assessment concludes that even with these improvements, a lower contribution of PEG4000 to the 2G bioethanol production costs would be needed to reach commercial feasibility.

Using polyvinylpyrrolidone to enhance the enzymatic hydrolysis of lignocelluloses by reducing the cellulase non-productive adsorption on lignin

Polyvinylpyrrolidone (PVP) is an antifouling polymer to resist the adsorption of protein on solid surface. Effects of PVP on the enzymatic hydrolysis of pretreated lignocelluloses and its mechanism were studied. Adding 1g/L of PVP8000, the enzymatic digestibility of eucalyptus pretreated by dilute acid (Eu-DA) was increased from 28.9% to 73.4%, which is stronger than the classic additives, such as PEG, Tween and bovine serum albumin. Compared with PEG4600, the adsorption of PVP8000 on lignin was larger, and the adsorption layer was more stable and hydrophilic. Therefore, PVP8000 reduced 73.1% of the cellulase non-productive adsorption on lignin and enhanced the enzymatic hydrolysis of lignocelluloses greatly.

Mechanisms of the inhibition of enzymatic hydrolysis of waste pulp fibers by calcium carbonate and the influence of nonionic surfactant for mitigation

Recycled paper mills produce large quantities of fibrous rejects and fines which are usually sent to landfills as solid waste. These cellulosic materials can be enzymatically hydrolyzed into sugars for the production of biofuels and biomaterials. Paper mill wastes also contain large amounts of calcium carbonate which inhibits cellulase activity. The calcium carbonate (30%, w/w) decreased 40-60% of sugar yield of unbleached softwood kraft pulp. The prime mechanisms for this are by pH variation, competitive and non-productive binding, and aggregation effect. Addition of acetic acid (pH adjustment) increased the sugar production from 19 to 22 g/L of paper mill waste fibers. Strong affinity of enzyme-calcium carbonate decreased free enzyme in solution and hindered sugar production. Electrostatic and hydrogen bond interactions are mainly possible mechanism of enzyme-calcium carbonate adsorption. The application of the nonionic surfactant Tween 80 alleviated the non-productive binding of enzyme with the higher affinity on calcium carbonate. Dissociated calcium ion also inhibited the hydrolysis by aggregation of enzyme.

Investigating the enzyme-lignin binding with surfactants for improved saccharification of pilot scale pretreated wheat straw

In this study, commercial surfactants have been investigated at economically viable dosage to enhance the enzymatic saccharification of pretreated wheat straw at high solid loadings. Twenty one surfactants were evaluated with pilot scale pretreated wheat straw and mechanism of surfactant action has been elucidated. One surfactant has improved the saccharification of dilute acid wheat straw (DAWS) by 26.4% after 24h and 23.1% after 48h while, steam exploded wheat straw (SEWS) saccharification was increased by 51.2% after 24h and 36.4% after 48h at 10% solid loading. At 20% solid loading, about 31% increase in yield was obtained on DAWS and about 55% on SEWS after 48h. Further, lignin was isolated from pretreated wheat straws and characterized which revealed that SEWS derived lignin was more hydrophobic than DAWS lignin. This investigation suggests that surfactant supplementation during saccharification is an effective strategy to achieve higher saccharification yield.

Epoxidation and etherification of alkaline lignin to prepare water-soluble derivatives and its performance in improvement of enzymatic hydrolysis efficiency

BACKGROUND

Due to the depletion of fossil resources and their environmental impact, woody biomass has received much attention as an alternative resource. Lignin, as the third most abundant biopolymer from biomass, is now considered as an excellent alternative feedstock for chemicals and materials. The conversion of lignin to the value-added products is a key process to achieve an integrated biorefinery of woody biomass. Among these value-added products, lignin-based derivatives with good surface activity can be applied to enhance the conversion of cellulose into fermentable sugars, which not only decrease the cost of bioethanol production, but also reduce the environmental pollution and green house effect resulting from the burning of fossil resources.

RESULTS

Water-soluble alkaline lignin was synthesized by the reaction between polyethylene glycols (PEG600 and PEG1000) and epoxy lignin. FT-IR and NMR analyses indicated that PEGs were successively introduced into epoxy alkaline lignin using potassium persulfate as a catalyst. Emulsification and surface activity tests indicated that the surface tension of the prepared lignin derivative solution was 43.30 mN/m at the critical micelle concentration (1.03 %). A stable emulsions layer was formed with hexanes and the emulsion particle diameter in the emulsion phase for all products was observed at 10-50 μm. The results of enzymatic hydrolysis indicated that the products derived from PEG1000-grafted lignin resulted in the highest increasing rate of 18.6 % of glucose yield during the enzymatic hydrolysis of hardwood bleached pulp. The results of fermentation experiments suggested that the product had no toxicity for fermentation micro-organisms.

CONCLUSION

Water-soluble alkaline lignin derivatives were prepared through epoxidation and etherification, which are promising feedstocks for detergents, emulsifier, and additive to enhance enzymatic hydrolysis efficiency and ethanol fermentation.

Efficient hydrolysis of corncob residue through cellulolytic enzymes from Trichoderma strain G26 and L-lactic acid preparation with the hydrolysate

To prepare fermentable hydrolysate from corncob residue (CCR), Trichoderma strain G26 was cultured on medium containing CCR for production of cellulolytic enzymes through solid-state fermentation (SSF), resulting in 71.3 IU/g (FPA), 136.2 IU/g (CMCase), 85.1 IU/g (β-glucosidase) and 11,344 IU/g (xylanase), respectively. Through a three-stage saccharification strategy, CCR was hydrolyzed by the enzymatic solution (6.5 FPU/ml) into fermentable hydrolysate containing 60.1g/l glucose (81.2% cellulose was converted at solid loading of 12.5%), 21.4% higher than that by the one-stage method. And then the hydrolysate was used to produce L-lactic acid by a previous screened strain Bacillus coagulans ZX25 in the submerged fermentation. 52.0 g/l L-lactic acid was obtained after fermentation for 44 h, with 86.5% glucose being converted to L-lactic acid. The results indicate that the strains and the hydrolysis strategy are promising for commercial production of L-lactic acid from CCR and other biomass.

Effect of non-enzymatic proteins on enzymatic hydrolysis and simultaneous saccharification and fermentation of different lignocellulosic materials

Non-enzymatic proteins were added during hydrolysis of cellulose and simultaneous saccharification and fermentation (SSF) of different biomass materials. Bovine serum albumin (BSA), a model non-enzymatic protein, increased cellulose and xylose conversion efficiency and also enhanced the ethanol yield during SSF of rice straw subjected to varied pretreatments. Corn steep liquor, yeast extract, and peptone also exerted a similar effect as BSA and enhanced the enzymatic hydrolysis of rice straw. Compared to the glucose yields obtained after enzymatic hydrolysis of rice straw in the absence of additives, the glucose yields after 72h of hydrolysis increased by 12.7%, 13.5%, and 13.7% after addition of the corn steep liquor, yeast extract, and peptone, respectively. This study indicated the use of BSA as an alternative to intensive pretreatment of lignocellulosic materials for enhancing enzymatic digestibility. The utilization of non-enzymatic protein additives is promising for application in glucose and ethanol production from lignocellulosic materials.

A study on cell surface hydrophobicity, growth and metabolism of Zymomonas mobilis influenced by PEG as a pretreatment agent

This study investigates the effects of polyethylene glycol (PEG) 4000, a non-ionic surfactant, on the cell surface hydrophobicity (CSH) ofZymomonas mobilis, as well as its growth and metabolism.

Tween 40 pretreatment of unwashed water-insoluble solids of reed straw and corn stover pretreated with liquid hot water to obtain high concentrations of bioethanol

BACKGROUND

Liquid hot water (LHW) pretreatment is an effective and environmentally friendly method to produce bioethanol with lignocellulosic materials. In our previous study, high ethanol concentration and ethanol yield were obtained from water-insoluble solids (WIS) of reed straw and corn stover pretreated with LHW by using fed-batch semi-simultaneous saccharification and fermentation (S-SSF). However, high cellulase loading and the large amount of wash water possibly limit the practical application of LHW pretreatment. To decrease cellulase loading and the amount of wash water, we performed Tween 40 pretreatment before WIS was subjected to bioethanol fermentation.

RESULTS

Results showed that the optimum conditions of Tween 40 pretreatment were as follows: Tween 40 concentration of 1.5%, WIS-to-Tween 40 ratio of 1:10 (w/v), and pretreatment time of 1 hour at ambient temperature. After Tween 40 pretreatment, cellulase loading could be greatly reduced. After Tween 40 pretreatment, the residual liquid could be recycled for utilization but slightly affected ethanol concentration and yield. The unwashed WIS could obtain a high ethanol concentration of 56.28 g/L (reed straw) and 52.26 g/L (corn stover) by Tween 40 pretreatment using fed-batch S-SSF. Ethanol yield reached a maximum of 69.1% (reed straw) and 71.1% (corn stover).

CONCLUSIONS

Tween 40 pretreatment was a very effective and less costly method with unwashed WIS. This pretreatment could greatly reduce cellulase loading and save wash water. Higher ethanol concentration was obtained almost without reducing ethanol yield.

Enzymatic hydrolysis and ethanol yields of combined surfactant and dilute ammonia treated sugarcane bagasse

Tween 80, Tween 20, PEG 4000 or PEG 6000 was used in combination with ammonium hydroxide for the pretreatment of sugarcane bagasse. Pretreatment was carried out by mixing sugarcane bagasse, ammonium hydroxide (28% v/v solution), and water at a ratio of 1:0.5:20, adding 3% (w/w) surfactant based on the weight of dry biomass, and heating the mixture to 160 °C for 1 h. Fibers were hydrolyzed using two concentrations of commercially available enzymes, Spezyme CP and Novozyme 188. The results indicated that PEG 4000 and Tween 80 gave the highest cellulose digestibilities (62%, 66%) and ethanol yields (73%, 69%) as compared to the use of only dilute ammonia (38%, 42%) or water (27%, 26%) as catalysts, respectively. The enhanced digestibilities of non-ionic surfactant–dilute ammonia treated biomass can be attributed to delignification and reduction of cellulose crystallinity as confirmed by FTIR, TGA and XRD analysis.

Numerical analysis of the impact of structural changes in cellulosic substrates on enzymatic saccharification

Here, a simple cellulose conversion model that considers the cellulose surface area and surface density of adsorbed cellulase as substrate-derived and cellulase-derived factors controlling reaction rates is provided. Microcrystalline cellulose (Avicel) and delignifed softwood were used as controls, and structure-modified samples were prepared. It was shown that the initial cellulose conversion rate is largely controlled by the cellulose surface area. Moreover, the proposed model demonstrates that increases in cellulose surface area reduce retardation of the cellulase reaction. The proposed model was used to estimate the impact of structural changes in a substrate (i.e., cellulose surface area) by pre-treatment on enzymatic saccharification. It was found that increasing the cellulose surface area is the most effective way to optimize enzymatic saccharification of cellulose substrates.