Adsorption of enzyme onto lignins of liquid hot water pretreated hardwoods

Fenton-ultrasound treatment of corn stalks enhances humification during composting by stimulating the inheritance and synthesis of polyphenolic compounds-preliminary evidence from a laboratory trial

The impact of Fenton-ultrasound treatment on the production of polyphenols and humic acid (HA) during corn stalk composting was investigated by analyzing the potential for microbial assimilation of polysaccharides in corn stalks to generate polyphenols using a13C-glucose tracer. The results showed that Fenton-ultrasound treatment promoted the decomposition of lignocellulose and increased the HA content, degree of polymerization (DP), and humification index (HI). The primary factor could be attributed to Fenton-ultrasound treatment-induced enhanced the abundance of lignocellulose-degrading microorganisms, as Firmicutes, Actinobacteria phylum and Aspergillis genus, which serve as the primary driving forces behind polyphenol and HA formation. Additionally, the utilization of a13C isotope tracer revealed that corn stalk polysaccharide decomposition products can be assimilated by microbes and subsequently secrete polyphenolic compounds. This study highlights the potential of microbial activity to generate phenolic compounds, offering a theoretical basis for increasing polyphenol production and promoting HA formation during composting.

The role of glycosylation in non-productive adsorption of cellulase to lignin isolated from pretreated corn stover

Glycosylation, a general post-translational modification for fungal cellulase, has been shown to affect cellulase binding to its substrate. However, the exact impact of glycosylation on cellulase-lignin interaction remain unclear. Here, we demonstrated that the lignin isolated from tetrahydrofuran-pretreated corn stover exhibits strong adsorption capability to cellulase due to its negatively charged and porous structure. For the cellulases with varying glycosylation levels, the less-glycosylated protein showed high adsorption capability to lignin, and that trend was observed for the main cellulase components secreted by Penicillium oxilicum, including endoglucanase PoCel5B, cellobiohydrolase PoCel7A-2, and β-glucosidase PoBgl1. Additionally, N-glycan sites and motifs were examined using mass spectrometry, and protein structures with N-glycans were constructed, where PoBgl1 and PoCel7A-2 contained 13 and 1 glycosylated sites respectively. The results of molecular dynamics simulations indicated that the N-glycans impacted on the solvent-accessible surface area and secondary structure of protein, and the binding conformation of lignin fragment on cellulase, resulting in a decrease in binding energy (14 kcal/mol for PoBgl1 and 13 kcal/mol for PoCel7A-2), particularly for van der Waals and electrostatic interaction. Those findings suggested that glycosylation negatively impacted the lignin-cellulase interaction, providing a theoretical basis for the rational engineering of enzymes to reduce lignin-enzyme interaction.

Evaluating the mechanism of soybean meal protein for boosting the laccase-catalyzed of thymol onto lignosulfonate via restraining non-specific adsorption

The control of laccase-catalyzed efficiency often relies on the utilization of modifying enzyme molecules and shielding agents. However, their elevated costs or carcinogenicity led to the inability for large-scale application. To address this concern, we found that a low-cost protein from soybean meal can reduce lignin's ineffective adsorption onto enzymes for improving the efficiency of thymol grafting to lignosulfonate. The results demonstrated that by adding 0.5 mg/mL of additional soybean meal protein, the thymol reaction ratio of the modified lignosulfonate (L-0.5 S) significantly boosted from 18.1 % to 35.0 %, with the minimal inhibitory concentrations of the L-0.5 S against Aspergillus niger dramatically improved from 12.5 mg/mL to 3.1 mg/mL. Multiple characterization methods were employed to better understand the benefit of the modification under the addition of the soybean meal protein. The CO and R1-O group content increased from 20.5 % to 37.8 % and from 65.1 % to 75.5 %, respectively. The proposed potential reaction mechanism was further substantiated by the physicochemical properties. The incorporation of soybean meal effectively mitigated the non-specific adsorption of lignosulfonate, resulting in a reduction of the surface area of lignin from 235.0 to 139.2 m2/g. The utilization of soybean meal as a cost-effective and efficient shielding agent significantly enhanced the efficiency of subsequent enzyme catalysis. Consequently, the application of soybean meal in commercial enzyme catalysis holds considerable appeal and amplifies the relevance of this study in preservative industries.

Molecular insights into inhibiting effects of lignin on cellulase investigated by molecular dynamics simulation

The hydrolysis of lignocellulose into fermentable monosaccharides using cellulases represents a critical stage in lignocellulosic bioconversion. However, the inactivation of cellulase in the presence of lignin is attributed to the high cost of biofinery. To address this challenge, a comprehensive investigation into the structure-function relationship underlying lignin-driven cellulase inactivation is essential. In this study, molecular docking and molecular dynamics (MD) simulations were employed to explore the impacts of lignin fragments on the catalytic efficiency of cellulase at the atomic level. The findings revealed that soluble lignin fragments and cellulose could spontaneously form stable complexes with cellulase, indicating a competitive binding scenario. The enzyme's structure remained unchanged upon binding to lignin. Furthermore, specific amino acid residues have been identified as involved in interactions with lignin and cellulose. Hydrophobic interactions were found to dominate the binding of lignin to cellulase. Based on the mechanisms underlying the interactions between lignin fragments and cellulase, decreased hydrophobicity and change in the charge of lignin may mitigate the inhibition of cellulase. Furthermore, site mutations and chemical modification are also feasible to improve the efficiency of cellulase. This study may contribute valuable insights into the design of more lignin-resistant enzymes and the optimization of lignocellulosic pretreatment technologies.Communicated by Ramaswamy H. Sarma.

Improving enzymatic efficiency of β-glucosidases in cellulase system by altering its binding behavior to the insoluble substrate during bioconversion of lignocellulose

The enzymatic efficiency of β-glucosidases is influenced by their binding behavior onto insoluble substrates (cellulose and lignin) during bioconversion of lignocellulose. This study suggested that the Bgl3 protein (Aspergillus fumigatus) showed strong adsorption affinity to lignin and the Bgl1 protein (Penicillium oxalicum) tended to adsorb to cellulose. It indicated that the various surface properties of the fibronectin type Ш-like domain (FnIII) led to different binding properties of β-glucosidases by investigating their binding mechanism. By engineering β-glucosidases' FnIII domain, Bgl3-1 and Bgl1-3 were constructed, which both showed lower binding capacities to insoluble substrates. As well as for Bgl1-3, its sensitivity to the phenolic component was also eased. Based on that, the reconstructed protein showed high catalytic efficiency during the enzymatic hydrolysis of corn stover by effectively transforming cellobiose to glucose. Thus, this study provided a new strategy to engineer β-glucosidases to enhance their performance in the cellulase system.

Recent advances in the synthesis and applications of single-atom nanozymes in food safety monitoring

Nanozymes are synthetic compounds with enzyme-like tunable catalytic properties. The success of nanozymes for catalytic applications can be attributed to their small dimensions, cost-effective synthesis, appreciable stability, and scalability to molecular dimensions. The emergence of single atom nanozymes (SANzymes) has opened up new possibilities in bioanalytical applications. In this regard, this review outlines enzyme-mimicking features of SANzymes for food safety applications in relation to the key variables controlling their catalytic performance. The discussion is extended further to cover the applications of SANzymes for the monitoring of various compounds/biomaterials of significance with respect to food safety (e.g., pesticides, veterinary drug residues, foodborne pathogenic bacteria, mycotoxins/bacterial endotoxin, antioxidant residues, hydrogen peroxide residues, and heavy metal ions). Furthermore, the performance of SANzymes is evaluated in terms of various performance metrics such as limit of detection (LOD), linear dynamic range, and figure of merit (FoM). The challenges and future road map for the applications of SANzymes are also addressed along with their upscaling in the area of food safety.

Unveiling the role of long-range and short-range forces in the non-productive adsorption between lignin and cellulases at different temperatures

Quantitatively understanding of interaction mechanism between lignin and cellulases is essential for the efficient improvement of lignocellulose enzymatic hydrolysis. However, the individual contribution of multiple forces between lignin and cellulases to the non-productive adsorption of enzymes still remains deeply ambiguous, especially in situations of near enzymatic hydrolysis temperatures. Herein, atomic force microscopy (AFM) and computational simulations were utilized to quantitatively analyze the intermolecular forces between lignin and enzyme at 25 °C and 40 °C. Our results unveiled that an increase in temperature obviously improved adsorption capacity and total intermolecular forces between lignin and cellulases. This positive relationship mainly comes from the increase in the decay length of hydrophobic forces for lignin-cellulases when temperature increases. Different from the hydrophobic interaction which provides long-range part of attractions, van der Waals forces dominate the intermolecular force only at approaches < 2 nm. On the other hand, electrostatic forces exhibited repulsive effects, and its intensity and distance were limited due to the low surface potential of cellulases. Short-range forces including hydrogen bonding (main) and π-π stacking (minor) stabilize the non-specific binding of enzymes to lignin, but increasing temperature reduces hydrogen bond number. Therefore, the relative contribution of long-range forces increased markedly at higher temperatures, which benefits protein capture and brings lignin and cellulase close together. Finally, the structure-activity relationships between lignin physicochemical properties and its inhibitory effect to enzymes indicated that hydrophobic interactions, hydrogen bonding, and steric effects drive the final adsorption capacity and glucose yields. This work provides quantitative and basic insights into the mechanism of lignin-cellulase interfacial interactions and guides design of saccharification enhancement approaches.

Exploring how lignin structure influences the interaction between carbohydrate-binding module and lignin using AFM

Nonproductive adsorption of cellulase onto the residual lignin in substrate seriously hinders the enzymatic hydrolysis. To understand how lignin structure affects lignin-cellulase interaction, the carbohydrate-binding module (CBM) functionalized atomic force microscope tip was used to measure CBM-lignin interaction by single-molecule dynamic force spectroscopy in this work. The results showed that sulfonated lignin (SL) has the greatest adhesion force to CBM (4.74 nN), while those of masson pine milled wood lignin (MWL), poplar MWL and herbaceous MWLs were 2.85, 1.03 and 0.27-0.61 nN, respectively. It provides direct quantitative evidence for the significance of lignin structure on lignin-cellulase interaction. The CBM-MWLs interaction decreased sharply to 0.054-0.083 nN while SL was added, indicating the primary mechanism of SL promoting lignocellulose hydrolysis was significantly reducing the nonproductive adsorption of substrate lignin on cellulase. Finally, the "competitive adsorption" mechanism was proposed to interpret why SL effectively promotes the enzymatic hydrolysis of lignin-containing substrates.

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.

Positive role of non-catalytic proteins on mitigating inhibitory effects of lignin and enhancing cellulase activity in enzymatic hydrolysis: Application, mechanism, and prospective

Fermentable sugar production from lignocellulosic biomass has received considerable attention and has been dramatic progress recently. However, due to low enzymatic hydrolysis (EH) yields and rates, a high dosage of the costly enzyme is required, which is a bottleneck for commercial applications. Over the last decades, various strategies have been developed to reduce cellulase enzyme costs. The progress of the non-catalytic additive proteins in mitigating inhibition in EH is discussed in detail in this review. The low efficiency of EH is mostly due to soluble lignin compounds, insoluble lignin, and harsh thermal and mechanical conditions of the EH process. Adding non-catalytic proteins into the EH is considered a simple and efficient approach to boost hydrolysis yield. This review discussed the multiple mechanical steps involved in the EH process. The effect of physicochemical properties of modified lignin on EH and its interaction with cellulase and cellulose are identified and discussed, which include hydrogen bonding, hydrophobic, electrostatic, and cation-π interactions, as well as physical barriers. Moreover, the effects of different conditions of EH that lead to cellulase deactivation by thermal and mechanical mechanisms are also explained. Finally, recent advances in the development, potential mechanisms, and economic feasibility of non-catalytic proteins on EH are evaluated and perspectives are presented.

Highly catalytic supramolecular host-guest complex for high value directional conversion of lignin to syringyl monomer

In order to meet the challenge of enzyme catalysis of waste lignin, laccase (LAC)- guaiacyl(G)-type monomers noncovalent supramolecular system (LGS) were constructed for conversion of lignin. In this contribution, the catalytic effect of LGS formed by LAC and G-type monomers was studied. LAC changes the secondary structure conformation of its binding site to accommodate the G-type monomer, which is bound by hydrogen bonding and hydrophobic interactions. A mechanistic study highlights that the non-covalent complexation accelerates the internal electron transfer rate of LGS and syringol substrate for subsequent coupling reactions. In the presence of guaiacol/4-ethylguaiacol/vanillin-LAC, the conversion of dealkali lignin were 16.44, 29.12 and 22.72, respectively, higher than that in the presence of LAC alone. And the product of syringyl monomer was significantly increased in the actual lignin catalysis. Our work explains the mechanisms underlying existing enzyme-substrate interactions and enhanced catalytic system can be used for efficient utilization of waste.

Inhibitor formation and detoxification during lignocellulose biorefinery: A review

For lignocellulose biorefinery, pretreatment is needed to maximize the cellulose accessibility, frequently generating excess inhibitory substances to decline the efficiency of the subsequent fermentation processes. This mini-review updates the current research efforts to detoxify the adverse impacts of generated inhibitors on the performance of biomass biorefinery. The lignocellulose pretreatment processes are first reviewed. The generation of inhibitors, furans, furfural, phenols, formic acid, and acetic acid, from the lignocellulose, with their action mechanisms, are listed. Then the detoxification processes are reviewed, from which the biological detoxification processes are noted as promising and worth further study. The challenges and prospects for applying biological detoxification in lignocellulose biorefinery are outlined. Integrated studies considering the entire biorefinery should be performed on a case-by-case basis.

Dissolved xylan inhibits cellulosome-based saccharification by binding to the key cellulosomal component of Clostridium thermocellum

Polysaccharides derived from lignocellulose are promising sustainable carbon sources. Cellulosome is a supramolecular machine integrating multi-function enzymes for effective lignocellulose bio-saccharification. However, how various non-cellulose components of lignocellulose affect the cellulosomal saccharification is hitherto unclear. This study first investigated the stability and oxygen sensitivity of the cellulosome from Clostridium thermocellum during long-term saccharification process. Then, the differential inhibitory effects of non-cellulose components, including lignin, xylan, and arabinoxylan, on the cellulosome-based saccharification were determined. The results showed that lignin played inhibitory roles by non-productively adsorbing extracellular proteins of C. thermocellum. Differently, arabinoxylan preferred to bind with the cellulosomal components. Almost no adsorption of cellulosomal proteins on solid xylan was detected. Instead, xylan in water-dissolved form interacted with the cellulosomal proteins, especially the key exoglucanase Cel48S, leading to the xylan inhibitory effect. Compared to xylan, xylooligosaccharides influenced the cellulosome activity slightly. Hence, this work demonstrates that the timely hydrolysis or removal of dissolved xylan is important for cellulosome-based lignocellulose saccharification.

An effective strategy for improving the specific activity and saccharification efficiency of cellulase by pre-incubation with phenolic acids

This short communication analyzed the effects of lignin-derived phenolic acid compounds on cellulase. Vanillic acid, syringic acid, ferulic acid, and isovanillic acid improved cellulase specific activity and saccharification efficiency. In the enzymatic hydrolysis process, the promotion effect of phenolic acid was concentration-dependent. The effect of low concentration of phenolic acids (less than 5 mM) was negligible. After pre-incubating 1 g cellulase with 5 mmol phenolic acid, FPase-specific activity, CMCase-specific activity, and pNPGase-specific activity increased by 57.06%, 136.79%, and 110.61%, respectively. After digestion with pre-incubated cellulase, the saccharification efficiency of phosphoric acid-swollen cellulose increased by 45.13%. Pre-incubation with phenolic acid improved the saccharification efficiency of cellulase. It might be helpful to enhance the comprehensive utilization capacity of lignin-derived compounds.

Current understanding and optimization strategies for efficient lignin-enzyme interaction: A review

From energy perspective, with abundant polysaccharides (45-85%), the renewable lignocellulosic is recognized as the 2nd generation feedstock for bioethanol and bio-based products production. Enzymatic hydrolysis is a critical pathway to yield fermentable monosaccharides from pretreated substrates of lignocellulose. Nevertheless, the lignin presence in lignocellulosic substrates leads to the low substrate enzymatic digestibility ascribed to the nonproductive adsorption. It has been reported that the water-soluble lignin (low molecular weight, sulfonated/sulfomethylated and graft polymer) enhance the rate of enzymatic digestibility, however, the catalytic mechanism of lignin-enzyme interaction remains elusive. In this review, optimization strategies for enzymatic hydrolysis based on the lignin structural modification, enzyme engineering, and different additives are critically reviewed. Lignin-enzyme interaction mechanism is also discussed (lignin and various cellulases). In addition, the mathematical models and simulation of lignin, cellulose and enzyme aims for promoting an integrated biomass-conversion process for sustainable production of value-added biofuels.

Development of a powerful synthetic hybrid promoter to improve the cellulase system of Trichoderma reesei for efficient saccharification of corncob residues

Background

The filamentous fungus Trichoderma reesei is a widely used workhorse for cellulase production in industry due to its prominent secretion capacity of extracellular cellulolytic enzymes. However, some key components are not always sufficient in this cellulase cocktail, making the conversion of cellulose-based biomass costly on the industrial scale. Development of strong and efficient promoters would enable cellulase cocktail to be optimized for bioconversion of biomass.

Results

In this study, a synthetic hybrid promoter was constructed and applied to optimize the cellulolytic system of T. reesei for efficient saccharification towards corncob residues. Firstly, a series of 5’ truncated promoters in different lengths were established based on the strong constitutive promoter Pcdna1. The strongest promoter amongst them was Pcdna1-3 (− 640 to − 1 bp upstream of the translation initiation codon ATG), exhibiting a 1.4-fold higher activity than that of the native cdna1 promoter. Meanwhile, the activation region (− 821 to − 622 bp upstream of the translation initiation codon ATG and devoid of the Cre1-binding sites) of the strong inducible promoter Pcbh1 was cloned and identified to be an amplifier in initiating gene expression. Finally, this activation region was fused to the strongest promoter Pcdna1-3, generating the novel synthetic hybrid promoter Pcc. This engineered promoter Pcc drove strong gene expression by displaying 1.6- and 1.8-fold stronger fluorescence intensity than Pcbh1 and Pcdna1 under the inducible condition using egfp as the reporter gene, respectively. Furthermore, Pcc was applied to overexpress the Aspergillus niger β-glucosidase BGLA coding gene bglA and the native endoglucanase EG2 coding gene eg2, achieving 43.5-fold BGL activity and 1.2-fold EG activity increase, respectively. Ultimately, to overcome the defects of the native cellulase system in T. reesei, the bglA and eg2 were co-overexpressed under the control of Pcc promoter. The bglA-eg2 double expression strain QPEB70 exhibited a 178% increase in total cellulase activity, whose cellulase system displayed 2.3- and 2.4-fold higher saccharification efficiency towards acid-pretreated and delignified corncob residues than the parental strain, respectively.

Conclusions

The synthetic hybrid promoter Pcc was generated and employed to improve the cellulase system of T. reesei by expressing specific components. Therefore, construction of synthetic hybrid promoters would allow particular cellulase genes to be expressed at desired levels, which is a viable strategy to optimize the cellulolytic enzyme system for efficient biomass bioconversion.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12934-021-01727-8.

Comparative Evaluation of Adsorption of Major Enzymes in a Cellulase Cocktail Obtained from Trichoderma reesei onto Different Types of Lignin

Cellulase adsorption onto lignin decreases the productivity of enzymatic hydrolysis of lignocellulosic biomass. Here, adsorption of enzymes onto different types of lignin was investigated, and the five major enzymes—cellobiohydrolases (CBHs), endoglucanase (Cel7B), β-glucosidase (Cel3A), xylanase (XYNIV), and mannanase (Man5A)—in a cellulase cocktail obtained from Trichoderma reesei were individually analyzed through SDS-PAGE and zymogram assay. Lignin was isolated from woody (oak and pine lignin) and herbaceous (rice straw and kenaf lignin) plants. The relative adsorption of CBHs compared to the control was in the range of 14.15–18.61%. The carbohydrate binding motif (CBM) of the CBHs contributed to higher adsorption levels in oak and kenaf lignin, compared to those in pine and rice lignin. The adsorption of endoglucanase (Cel7B) by herbaceous plant lignin was two times higher than that of woody lignin, whereas XYNIV showed the opposite pattern. β-glucosidase (Cel3A) displayed the highest and lowest adsorption ratios on rice straw and kenaf lignin, respectively. Mannanase (Man5A) was found to have the lowest adsorption ratio on pine lignin. Our results showed that the hydrophobic properties of CBM and the enzyme structures are key factors in adsorption onto lignin, whereas the properties of specific lignin types indirectly affect adsorption.

Liquid hot water as sustainable biomass pretreatment technique for bioenergy production: A review

In recent years, lignocellulosic biomass has emerged as one of the most versatile energy sources among the research community for the production of biofuels and value-added chemicals. However, biomass pretreatment plays an important role in reducing the recalcitrant properties of lignocellulose, leading to superior quality of target products in bioenergy production. Among existing pretreatment techniques, liquid hot water (LHW) pretreatment has several outstanding advantages compared to others including minimum formation of monomeric sugars, significant removal of hemicellulose, and positive environmental impacts; however, several constraints of LHW pretreatment should be clarified. This contribution aims to provide a comprehensive analysis of reaction mechanism, reactor characteristics, influencing factors, techno-economic aspects, challenges, and prospects for LHW-based biomass pretreatment. Generally, LHW pretreatment could be widely employed in bioenergy processing from biomass, but circular economy-based advanced pretreatment techniques should be further studied in the future to achieve maximum efficiency, and minimum cost and drawbacks.

Knockout of the lignin pathway gene BnF5H decreases the S/G lignin compositional ratio and improves Sclerotinia sclerotiorum resistance in Brassica napus

Ferulate-5-hydroxylase is a key enzyme involved in the conversion of the guaiacyl monolignol to the syringyl monolignol in angiosperms. The monolignol ratio has been proposed to affect biomass recalcitrance and the resistance to plant disease. Stem rot caused by the fungus Sclerotinia sclerotiorum in Brassica napus causes severe losses in its production. To date, there is no information about the effect of the lignin monomer ratio on the resistance to S. sclerotiorum in B. napus. Four dominantly expressed ferulate-5-hydroxylase genes were concertedly knocked out by CRISPR/Cas9 in B. napus, and three mutant lines were generated. The S/G lignin compositional ratio was decreased compared to that of the wild type based on the results of Mӓule staining and 2D-NMR profiling in KO-7. The resistance to S. sclerotiorum in stems and leaves increased for the three f5h mutant lines compared with WT. Furthermore, we found that the stem strength of f5h mutant lines was significantly increased. Overall, we demonstrate for the first time that decreasing the S/G ratio by knocking out of the F5H gene improves S. sclerotiorum resistance in B. napus and increases stem strength.

Severity factor kinetic model as a strategic parameter of hydrothermal processing (steam explosion and liquid hot water) for biomass fractionation under biorefinery concept

Hydrothermal processes are an attractive clean technology and cost-effective engineering platform for biorefineries based in the conversion of biomass to biofuels and high-value bioproducts under the basis of sustainability and circular bioeconomy. The deep and detailed knowledge of the structural changes by the severity of biomasses hydrothermal fractionation is scientifically and technological needed in order to improve processes effectiveness, reactors designs, and industrial application of the multi-scale target compounds obtained by steam explosion and liquid hot water systems. The concept of the severity factor [log₁₀ (R_o)] established>30 years ago, continues to be a useful index that can provide a simple descriptor of the relationship between the operational conditions for biomass fractionation in second generation of biorefineries. This review develops a deep explanation of the hydrothermal severity factor based in lignocellulosic biomass fractionation with emphasis in research advances, pretreatment operations and the applications of severity factor kinetic model.

Recent advances in understanding the effects of lignin structural characteristics on enzymatic hydrolysis

Enzymatic hydrolysis of lignocellulose for bioethanol production shows a great potential to remit the rapid consumption of fossil fuels, given the fact that lignocellulose feedstocks are abundant, cost-efficient, and renewable. Lignin results in low enzymatic saccharification by forming the steric hindrance, non-productive adsorption of cellulase onto lignin, and deactivating the cellulase. In general, the non-productive binding of cellulase on lignin is widely known as the major cause for inhibiting the enzymatic hydrolysis. Pretreatment is an effective way to remove lignin and improve the enzymatic digestibility of lignocellulose. Along with removing lignin, the pretreatment can modify the lignin structure, which significantly affects the non-productive adsorption of cellulase onto lignin. To relieve the inhibitory effect of lignin on enzymatic hydrolysis, enormous efforts have been made to elucidate the correlation of lignin structure with lignin-enzyme interactions but with different views. In addition, contrary to the traditional belief that lignin inhibits enzymatic hydrolysis, in recent years, the addition of water-soluble lignin such as lignosulfonate or low molecular-weight lignin exerts a positive effect on enzymatic hydrolysis, which gives a new insight into the lignin-enzyme interactions. For throwing light on their structure-interaction relationship during enzymatic hydrolysis, the effect of residual lignin in substrate and introduced lignin in hydrolysate on enzymatic hydrolysis are critically reviewed, aiming at realizing the targeted regulation of lignin structure for improving the saccharification of lignocellulose. The review is also focused on exploring the lignin-enzyme interactions to mitigate the negative impact of lignin and reducing the cost of enzymatic hydrolysis of lignocellulose.

Unlocking the secret of lignin-enzyme interactions: Recent advances in developing state-of-the-art analytical techniques

Bioconversion of renewable lignocellulosics to produce liquid fuels and chemicals is one of the most effective ways to solve the problem of fossil resource shortage, energy security, and environmental challenges. Among the many biorefinery pathways, hydrolysis of lignocellulosics to fermentable monosaccharides by cellulase is arguably the most critical step of lignocellulose bioconversion. In the process of enzymatic hydrolysis, the direct physical contact between enzymes and cellulose is an essential prerequisite for the hydrolysis to occur. However, lignin is considered one of the most recalcitrant factors hindering the accessibility of cellulose by binding to cellulase unproductively, which reduces the saccharification rate and yield of sugars. This results in high costs for the saccharification of carbohydrates. The various interactions between enzymes and lignin have been explored from different perspectives in literature, and a basic lignin inhibition mechanism has been proposed. However, the exact interaction between lignin and enzyme as well as the recently reported promotion of some types of lignin on enzymatic hydrolysis is still unclear at the molecular level. Multiple analytical techniques have been developed, and fully unlocking the secret of lignin-enzyme interactions would require a continuous improvement of the currently available analytical techniques. This review summarizes the current commonly used advanced research analytical techniques for investigating the interaction between lignin and enzyme, including quartz crystal microbalance with dissipation (QCM-D), surface plasmon resonance (SPR), attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy, atomic force microscopy (AFM), nuclear magnetic resonance (NMR) spectroscopy, fluorescence spectroscopy (FLS), and molecular dynamics (MD) simulations. Interdisciplinary integration of these analytical methods is pursued to provide new insight into the interactions between lignin and enzymes. This review will serve as a resource for future research seeking to develop new methodologies for a better understanding of the basic mechanism of lignin-enzyme binding during the critical hydrolysis process.

Hot Compressed Water Pretreatment and Surfactant Effect on Enzymatic Hydrolysis Using Agave Bagasse

Agave bagasse is a residual biomass in the production of the alcoholic beverage tequila, and therefore, it is a promising raw material in the development of biorefineries using hot compressed water pretreatment (hydrothermal processing). Surfactants application has been frequently reported as an alternative to enhance monomeric sugars production efficiency and as a possibility to reduce the enzyme loading required. Nevertheless, the surfactant’s action mechanisms in the enzymatic hydrolysis is still not elucidated. In this work, hot compressed water pretreatment was applied on agave bagasse for biomass fractionation at 194 °C in isothermal regime for 30 min, and the effect of non-ionic surfactants (Tween 20, Tween 80, Span 80, and Polyethylene glycol (PEG 400)) was studied as a potential enhancer of enzymatic saccharification of hydrothermally pretreated solids of agave bagasse (AGB). It was found that non-ionic surfactants show an improvement in the conversion yield of cellulose to glucose (100%) and production of glucose (79.76 g/L) at 15 FPU/g glucan, the highest enhancement obtained being 7% regarding the control (no surfactant addition), using PEG 400 as an additive. The use of surfactants allows improving the production of fermentable sugars for the development of second-generation biorefineries.

Construction of a structural enzyme adsorption/kinetics model to elucidate additives associated lignin-cellulase interactions in complex bioconversion system

Enzymatic hydrolysis is a rate-limiting process in lignocellulose biorefinery. The reaction involves complex enzyme-substrate and enzyme-lignin interactions in both liquid and solid phases, and has not been well characterized numerically. In this study, a kinetic model was developed to incorporate dynamic enzyme adsorption and product inhibition parameters into hydrolysis simulation. The enzyme adsorption coefficients obtained from Langmuir isotherm were fed dynamically into first-order kinetics for simulating the equilibrium enzyme adsorption in hydrolysis. A fractal and product inhibition kinetics was introduced and successfully applied to improve the simulation accuracy on adsorbed enzyme and glucose concentrations at different enzyme loadings, lignin contents, and in the presence of bovine serum albumin (BSA) and lysozyme. The model provided numerical proof quantifying the beneficial effects of both additives, which improved the hydrolysis rate by reducing the nonproductive adsorption of enzyme on lignin. The hydrolysis rate coefficient and fractal exponent both increased with increasing enzyme loadings, and lignin inhibition exhibited with increasing fractal exponent. Compared with BSA, the addition of lysozyme exhibited higher hydrolysis rates, which was reflected in the larger hydrolysis rate coefficients and smaller fractal exponents in the simulation. The model provides new insights to support process development, control, and optimization.

Effect of lignin-blocking agent on enzyme hydrolysis of acid pretreated hemp waste

Hemp wastes (stems and branches), fractionated after hemp flower extraction for the production of cannabidiol oil, were utilized as a potentially renewable resource for the sugar flatform process. Hydrolysis of cellulose from the acid pretreated hemp biomass using a commercial enzyme was tested and evaluated for its chemical composition, morphological change, and sugar recovery. Acid pretreated hemp stems and branches, containing 1% glucan (w/v) solids, were hydrolyzed for 72 h using 25 mg enzyme protein per g glucan. A 54% glucose conversion was achieved from the treated branches versus a 71% yield from the treated stems. Raw branches and stems yielded 35% and 38% glucose, respectively. Further tests with a lignin-blocking additive (e.g. bovine serum albumin) resulted in a 72% glucose yield increase for stem hydrolysis using 10 mg enzyme protein per g glucan. While pretreatment promotes amorphous hemicellulose decrease and cellulose decomposition, it causes enzyme inhibition/deactivation due to potential inhibitors (phenols and lignin-derived compounds). This study confirms the addition of non-catalytic proteins enhances the cellulose conversion by avoiding non-productive binding of enzymes to the lignin and lignin-derived molecules, with lignin content determining the degree of inhibition and conversion efficiency.

The Pretreatment of Lignocelluloses With Green Solvent as Biorefinery Preprocess: A Minor Review

Converting agriculture and forestry lignocellulosic residues into high value-added liquid fuels (ethanol, butanol, etc.), chemicals (levulinic acid, furfural, etc.), and materials (aerogel, bioresin, etc.) via a bio-refinery process is an important way to utilize biomass energy resources. However, because of the dense and complex supermolecular structure of lignocelluloses, it is difficult for enzymes and chemical reagents to efficiently depolymerize lignocelluloses. Strikingly, the compact structure of lignocelluloses could be effectively decomposed with a proper pretreatment technology, followed by efficient separation of cellulose, hemicellulose and lignin, which improves the conversion and utilization efficiency of lignocelluloses. Based on a review of traditional pretreatment methods, this study focuses on the discussion of pretreatment process with recyclable and non-toxic/low-toxic green solvents, such as polar aprotic solvents, ionic liquids, and deep eutectic solvents, and provides an outlook of the industrial application prospects of solvent pretreatment.

Protective effects of non-catalytic proteins on endoglucanase activity at air and lignin interfaces

The manner in which added non-catalytic proteins during enzymatic hydrolysis of lignocellulosic substrates enhances hydrolysis mechanisms is not completely understood. Prior research has indicated that a reduction in the non-specific adsorption of enzymes on lignin, and deactivation of enzymes exposed to air-liquid interface provide rationale. This work investigated root causes including effects of the air-liquid interface on non-catalytic proteins, and effects of lignin on endoglucanase. Three different experimental designs and three variables (air-liquid interfacial area, the types of lignin (acid or enzymatic lignin), and the presence of non-enzymatic protein (bovine serum albumin [BSA] or soy proteins ) were used. The results showed that acid isolated lignin adsorbed almost all endoglucanase activity initially present in supernatant, independent of air interface conditions (25 or 250 ml flasks) with the presence of BSA preventing this effect. Endoglucanase lost 30%-50% of its activity due to an air-liquid interface in the presence of lignin while addition of non-enzymatic protein helped to preserve this enzyme's activity. Langmuir and Freundlich models applied to experimental data indicated that the adsorption increases with increasing temperature for both endoglucanase and BSA. Adsorption of the enzyme and protein were endothermic with an increase in entropy. These results, combined, show that hydrophobicity plays a strong role in the adsorption of both endoglucanase and BSA on lignin.

Design of experiments driven optimization of alkaline pretreatment and saccharification for sugarcane bagasse

To maximize the sugar release from sugarcane bagasse, a high-resolution Fractional Factorial Design (FFD) was combined with a Central Composite Orthogonal (CCO) design to simultaneously evaluate a wide range of variables for alkaline pretreatment (NaOH: 0.1-1 mol/L, temperature: 100-220 °C, and time: 20-80 min) and enzymatic saccharification (enzyme loading: 2.5-17.5%, and reaction volume: 550-850 µL). A total of 46 experimental conditions were evaluated and the maximum sugar yield (423 mg/g) was obtained after 18 h enzymatic hydrolysis under optimized conditions (0.25 mol/L NaOH at 202 °C for 40 min, with 12.5% of enzyme loading). Biomass compositional analyses showed that the pretreatments strongly removed lignin (up to 70%), silica (up to 80%) and promoted cellulose enrichment (25-110%). This robust design of experiments resulted in maximizing enzymatic hydrolysis efficiency of sugarcane bagasse and further indicated that this combined approach is versatile for other lignocellulosic biomasses.

Balancing sugar recovery and inhibitor generation during energycane processing: Coupling cryogenic grinding with hydrothermal pretreatment at low temperatures

Pretreatment of lignocellulosic biomass at high temperatures or with oxidizing chemicals generate various inhibitors that restrict the efficient bioconversion of sugars in subsequent steps. The present study systematically investigates individual and combinatorial effects of pretreatment parameters on the generation of inhibitors. A plot between pretreatment temperature and inhibitor revealed optimum pretreatment temperature for energycane bagasse i.e., 170 °C beyond which total inhibitor production increased exponentially. No inhibitor production was observed on mechanical processing i.e., disk milling/cryogenic grinding of biomass. Evaluation of response surface regression exhibited that biomass solids loading has a significant effect on inhibitor generation at higher temperatures. The concentrations of certain inhibitors such as acetic acid, furfurals, and HMF increased more than 3-folds on doubling the solids loading. Furthermore, a novel low-severity approach of low-temperature hydrothermal pretreatment coupled with cryogenic grinding for lignocellulosic biomasses has been introduced which improved sugar yields while maintaining a low inhibitor concentration.

Charge-oriented strategies of tunable substrate affinity based on cellulase and biomass for improving in situ saccharification: A review

The intrinsic recalcitrance of lignocellulosic biomass makes it resistant to enzymatic hydrolysis. The electron-rich surface of the lignin and cellulose-alike structure of hemicellulose competitively absorb the cellulase. Thus, modifying the surface charge on biomass components to alter cellulase affinity is an urgent requisite. Developing charge tunable cellulase will alter substrate affinity. Also, charge-based immobilization generates controllable substrate affinity. Within immobilized cellulase involved in situ biomass saccharification, charge effects made a crucial contribution. In addition to affecting the interaction between immobilized cellulase and biomass, charge exerts an impact on cellulase to immobilize the materials, further investigation is essential. This study aims to review the charge effects on the cellulase affinity in biomass saccharification, strategies of charge tunable cellulase, and immobilized cellulase, thereby explaining the role of electrostatic interaction. In terms of electrostatic behavior, the pathways and plans to improve in situ biomass saccharification seem to be promising.

Combination of CTec2 and GH5 or GH26 Endo-Mannanases for Effective Lignocellulosic Biomass Degradation

Among endo-mannanases, glycoside hydrolase (GH) family 26 enzymes have been shown to be more catalytically active than GH5 enzymes on mannans. However, only GH5 endo-mannanases have been used for the formulation of enzyme cocktails. In this study, Bacillus sp.-derived GH5 and GH26 endo-mannanases were comparatively analysed biochemically for their synergistic action with a commercial cellulase blend, CTec2, during pre-treated lignocellulose degradation. Substrate specificity and thermo-stability studies on mannan substrates showed that GH26 endo-mannanase was more catalytically active and stable than GH5. GH26 also exhibited higher binding affinity for mannan than GH5, while GH5 showed more affinity for lignocellulosic substrates than GH26. Applying the endo-mannanases in combination with CTec2 for lignocellulose degradation led to synergism with a 1.3-fold increase in reducing sugar release compared to when CTec2 was used alone. This study showed that using the activity of endo-mannanases displayed with model substrates is a poor predictor of their activity and synergism on complex lignocelluloses.

Tracing Sweetgum Lignin's Molecular Properties through Biorefinery Processing

Changes to the molecular properties of lignin over the course of biorefinery processing were investigated by using sweetgum as a feedstock. Hydrothermal pretreatment has been used because it is an economically attractive, green process. Three representative biorefinery lignin preparations were obtained, with about 70 % yield based on raw lignin. The three fractions included soluble lignin adsorbed on resin (XADL), solvent-extracted lignin (HTCELp), and an additional ball-milled residual lignin (HTRELp). By comparing the raw and biorefinery lignin preparations, it can be concluded that lignin undergoes both degradation and condensation throughout the various stages of the hydrothermal-based biorefinery process. The two fractions made soluble by biorefinery processing, XADL and HTCELp, were found to be low-molecular-weight degradation products enriched with free phenolic hydroxyl groups. In addition, about 15 % of noncondensed phenolic units were involved in condensation reactions. Quantitative NMR spectroscopy analysis revealed that at least about 28 % of β-O-4' substructures were cleaved. Hibbert's ketones were identified in XADL and HTRELp, which provided evidence of lignin undergoing acidolysis. The contents of β-5' and β-β' did not change significantly upon biorefinery processing. Finally, episyringaresinol was detected in XADL and HTCELp. It is hoped that these findings will help to further demonstrate the specific effects of biorefinery processing on lignin in hardwood and facilitate its utilization to improve biorefinery economics.

Using highly recyclable sodium caseinate to enhance lignocellulosic hydrolysis and cellulase recovery

Most additives that capable of enhancing enzymatic hydrolysis of lignocellulose are petroleum-based, which are not easy to recycle with poor biodegradability. In this work, highly recyclable and biodegradable sodium caseinate (SC) was used to enhance lignocellulosic hydrolysis with improved cellulase recyclability. When the pH decreased from 5.5 to 4.8, more than 96% SC could be precipitated from the solution and recovered. Adding SC increased enzymatic digestibility of dilute acid pretreated eucalyptus (Eu-DA) from 39.5% to 78.2% under Eu-DA loading of 10 wt% and pH = 5.5, and increase cellulase content in 72 h hydrolysate from only 15.2% of the original to 60.0%, which facilitated the recovery of cellulases through re-adsorption by fresh substrates. With multiple cycles of re-adsorption, application of SC not only increased the sugar yield of Eu-DA by 95.5%, but also reduced cellulase loading by 40%.

Performance targets defined by retro-techno-economic analysis for the use of soybean protein as saccharification additive in an integrated biorefinery

The use of additives in the enzymatic saccharification of lignocellulosic biomass can have positive effects, decreasing the unproductive adsorption of cellulases on lignin and reducing the loss of enzyme activity. Soybean protein stands out as a potential lignin-blocking additive, but the economic impact of its use has not previously been investigated. Here, a systematic evaluation was performed of the process conditions, together with a techno-economic analysis, for the use of soybean protein in the saccharification of hydrothermally pretreated sugarcane bagasse in the context of an integrated 1G-2G ethanol biorefinery. Statistical experimental design methodology was firstly applied as a tool to select the process variable solids loading at 15% (w/w) and soybean protein concentration at 12% (w/w), followed by determination of enzyme dosage at 10 FPU/g and hydrolysis time of 24 h. The saccharification of sugarcane bagasse under these conditions enabled an increase of 26% in the amount of glucose released, compared to the control without additive. The retro-techno-economic analysis (RTEA) technique showed that to make the biorefinery economically feasible, some performance targets should be reached experimentally such as increasing biomass conversion to ideally 80% and reducing enzyme loading to 5.6 FPU/g in the presence of low-cost soybean protein.

Lignin extracted by γ-valerolactone/water from corn stover improves cellulose enzymatic hydrolysis

The impact of lignin extracted from γ-valerolactone/water (GVL/H₂O) pretreatment of corn stover on the enzymatic hydrolysis of cellulose was investigated. Two lignin samples were separated and named as GL25 and GL75 according to the amounts of sulfuric acid (25 mM and 75 mM) used in the GVL/H₂O pretreatment. With the addition of 2 g/L of GL25 and GL75, the glucan conversion of enzymatic hydrolysis of Avicel improved markedly from 28.0% to 37.4% and 31.3%, respectively. Moreover, the improvement of glucan conversion increased when increasing the loadings of GL25 and GL75. A similar observation was made when GVL/H₂O pretreated corn stover was the substrate. The results of the cellulase adsorption experiments showed that the GLs had a lower maximum cellulase adsorption capacity and binding strength compared to that of acid-insoluble lignin. Further structural characterization of the GLs revealed that they had a low zeta-potential and hydrophobicity, but a high Syringyl/Guaiacyl ratio.

Effect of Lignin Content on Cellulolytic Saccharification of Liquid Hot Water Pretreated Sugarcane Bagasse

Lignin contributes to the rigid structure of the plant cell wall and is partially responsible for the recalcitrance of lignocellulosic materials to enzymatic digestion. Overcoming this recalcitrance is one the most critical issues in a sugar-flat form process. This study addresses the effect of low lignin sugarcane bagasse on enzymatic hydrolysis after liquid hot water pretreatment at 190 °C and 20 min (severity factor: 3.95). The hydrolysis of bagasse from a sugarcane line selected for a relatively low lignin content, gave an 89.7% yield of cellulose conversion to glucose at 40 FPU/g glucan versus a 68.3% yield from a comparably treated bagasse from the high lignin bred line. A lower enzyme loading of 5 FPU/g glucan (equivalent to 3.2 FPU/g total solids) resulted in 31.4% and 21.9% conversion yields, respectively, for low and high lignin samples, suggesting the significance of lignin content in the saccharification process. Further increases in the enzymatic conversion of cellulose to glucose were achieved when the bagasse sample was pre-incubated with a lignin blocking agent, e.g., bovine serum albumin (50 mg BSA/g glucan) at 50 °C for 1 h prior to an actual saccharification. In this work, we have demonstrated that even relatively small differences in lignin content can result in considerably increased sugar production, which supports the dissimilarity of bagasse lignin content and its effects on cellulose digestibility. The increased glucose yields with the addition of BSA helped to decrease the inhibition of non-productive absorption of cellulose enzymes onto lignin and solid residual lignin fractions.

The residue from the acidic concentrated lithium bromide treated crop residue as biochar to remove Cr (VI)

In this work, the hydrolysis residue produced from the acidic concentrated lithium bromide hydrolysis (ALBH) of wheat straw, corn stover and elephant grass were characterized as biochar. The ALBH biochar as the black power had high content of carbon (49.65-55 wt%), specific surface areas (4.53-7.79 m²/g), porous structures (micropores, mesopores and macropores) and abundant oxygen functional groups (hydroxy, carbonyl, ester and ketone groups). These properties made ALBH biochar as a potential adsorbent for environmental remediation, with relatively high removal efficiency for a variety of heavy metal ions, especially hexavalent chromium (Cr(VI)). Therefore, ALBH technology may be an efficient strategy for synthesis of bio-char along with fermentable sugars, which met the concern of sustainability and green chemistry.

Effect of cellulolytic enzyme binding on lignin isolated from alkali and acid pretreated switchgrass on enzymatic hydrolysis

In this research, the binding of cellulolytic enzymes in Cellic^® CTec2 on six lignin isolates obtained from alkali (0.5, 1.0, and 1.5% NaOH at 121 °C for 30 min) and acid (1, 2, and 3% H₂SO₄ at 121 °C for 60 min) pretreated switchgrass was investigated. Briefly, the hydrolysis of cellobiose and Avicel with and without (control) lignin isolates was performed via CTec2 (5 and 10 FPU g^-1 carbohydrate) to determine whether the presence of lignin and binding of cellulolytic enzymes to the isolated lignin can affect the sugar production using three carbohydrate-lignin loadings, namely, 0.5:0.25, 0.5:0.5, and 0.5:1.0% (wv^-1). Based on SDS-PAGE results, β-glucosidase (BG) was significantly bound to all lignin isolates. Some enzymes in CTec2 presumed to be cellobiohydrolases, endo-1,4-β-glucanases, and xylanase, were also observed to partially bind to the lignin isolates. Up to 0.97 g glucose g^-1 cellobiose was produced via hydrolysis (72 h and pH 4.8) with CTec2 (5 and 10 FPU g^-1 carbohydrate). Similarly, up to 0.23 and 0.46 g glucose g^-1 Avicel were produced via hydrolysis (72 h and pH 4.8) with 5 and 10 FPU g^-1 carbohydrate, respectively. Results indicated that the addition of lignin isolates during cellobiose and Avicel hydrolysis did not significantly (p > 0.05) reduce glucose production regardless of type and amount of lignin isolate. Hence, even though BG was significantly bound to lignin isolates, it could maintain its functionality as a biological catalyst in this study.

Structural changes of lignins in natural Populus variants during different pretreatments

In the present study, three leading pretreatment technologies including dilute acid (DA), liquid hot water (LHW), and organosolv pretreatments (OS) were applied on two Populus natural variants with different recalcitrance. The structural features of the isolated lignins were analyzed accordingly. All the studied pretreatments reduced the molecular weights of the lignins. Aliphatic OH was reduced while phenolic OH was increased in all pretreated lignins. HSQC analysis revealed that pretreatment influenced the lignin composition and relative distribution of inter-unit linkages. The lignin S/G ratio was found to increase during DA pretreatment, while it was decreased after LHW and OS pretreatment. LHW pretreatment also resulted in much less cleavage of β-O-4 linkage than the other two pretreatments. These results could offer guidelines on appropriate selection of biomass and pretreatment technology in the future biorefinery process.

Enhancement of high-solids enzymatic hydrolysis efficiency of alkali pretreated sugarcane bagasse at low cellulase dosage by fed-batch strategy based on optimized accessory enzymes and additives

Obtaining higher amount of final sugars with low cellulase dosage has great economic benefits for the industrial biorefinery of lignocellulosic biomass. The optimization of accessory enzymes and additives were performed using single factor and orthogonal experiment firstly, after that, fed-batch strategy was applied to enhance the high-solids enzymatic hydrolysis efficiency of alkali pretreated sugarcane bagasse (SCB). A novel enzymatic hydrolysis procedure with 22% (w/v) substrate content and cellulase dosage of only 4 FPU/g dry biomass (DM) was developed, after digested for 48 h, the achieved glucose titer, yield and productivity were 122 g/L, 80% and 2.54 g L^-1 h^-1, respectively. Results obtained in this study indicated a potential finding for the industrial application of lignocellulosic biomass.

Selective deconstruction of hemicellulose and lignin with producing derivatives by sequential pretreatment process for biorefining concept

For improving the economic efficiency of the biorefining concept, selective decomposition and separation of biomass components is indispensable. In this respect, a sequential pretreatment process consisting of liquid hot water treatment and diluted peracetic acid (PAA) treatment was proposed for total utilization of lignocellulosic woody biomass. During the liquid hot water treatment, hemicellulose can be decomposed efficiently without significant loss of cellulose and lignin, implying the possibility for xylooligomer production by thermochemical treatment. In the PAA treatment, lignin was successfully degraded and liquefied using a 50% diluted PAA solvent, suggesting the possibility of dicarboxylic acid production. After the sequential process proposed in this study, the cellulose accessibility to the enzyme could be maximized by inducing selective deconstruction of hemicellulose and lignin.

Effect of Enzyme Interaction with Lignin Isolated from Pretreated Miscanthus x gigantues on Cellulolytic Efficiency

The effect of binding between the lignin isolates from an alkali (NaOH)– and an acid (H2SO4)– pretreated Miscanthus and cellulolytic enzymes in Cellic® CTec2 was investigated. Additonally, cellobiose and Avicel were enzymatically hydrolyzed with and without lignin isolates to study how enzyme binding onto lignin affects its conversion to glucose. Three carbohydrate–lignin loadings (0.5:0.25, 0.5:0.5, and 0.5:1.0% (w/v)) were employed. The results indicated that β-glucosidase (BG) had a strong tendency to bind to all lignin isolates. The overall tendency of enzyme binding onto lignin isolate was similar regardless of pretreatment chemical concentration. Though enzyme binding onto lignin isolates was observed, hydrolysis in the presence of these isolates did not have a significant (p > 0.05) impact on glucose production from cellobiose and Avicel. Cellobiose to glucose conversion of 99% was achieved via hydrolysis at both 5 and 10 FPU/g carbohydrate. Hydrolysis of Avicel with 5 and 10 FPU/g CTec2 resulted in 29.3 and 47.7% conversion to glucose, respectively.

Improvement of Anaerobic Digestion of Lignocellulosic Biomass by Hydrothermal Pretreatment

Lignocellulosic biomass, comprising of cellulose, hemicellulose, and lignin, is a difficult-to-degrade substrate when subjected to anaerobic digestion. Hydrothermal pretreatment of lignocellulosic biomass could enhance the process performance by increasing the generation of methane, hydrogen, and bioethanol. The recalcitrants (furfurals, and 5-HMF) could be formed at high temperatures during hydrothermal pretreatment of lignocellulosic biomass, which may hinder the process performance. However, the detoxification process involving the use of genetically engineered microbes may be a promising option to reduce the toxic effects of inhibitors. The key challenge lies in the scaleup of the hydrothermal process, mainly due to necessity of upholding high temperature in sizeable reactors, which may demand high capital and operational costs. Thus, more efforts should be towards the techno-economic feasibility of hydrothermal pre-treatment at full scale.