Enzymatic Hydrolysis Of Biomass Research Articles

Effect of microwave pretreatment on lignocellulosic degradation of corn cob

Lignocellulosic biomass is a widespread and renewable alternative to fossil resources from which valuable products such as biofuels and chemicals can be obtained. The usual biotechnological way of lignocellulose processing involves pre-treatment of biomass and enzymatic hydrolysis of complex carbohydrates (cellulose and hemicellulose) to simple sugars. The aim of this study was to examine the effect of microwave pretreatment on lignocellulosic degradation of corn cob. Biomass will be treated in a microwave oven (Bosch Serie 2, Germany) using hydrogen peroxide, under different conditions (pH and treatment time). After treatment, the solid fraction was subjected to enzymatic hydrolysis using the commercial enzyme CellicCTec2 (Novozymes, Denmark). The effect of the treatment was determined by determining the surface area of cellulose and lignin (based on the equation of Langmuir adsorption isotherm for adsorption of Congo red and Azure B, respectively), and the crystallinity index (iodine adsorption method). Enzymatic hydrolysis of biomass was monitored using spectrophotometric methods to determine the concentration of reducing sugars (DNS method), total hexose sugars (Antron method) and total pentose sugars (Orcinol method). The results of the treated samples were compared with the untreated ones in order to determine the most efficient treatment conditions for the degradation of lignocellulosic biomass.

Production of fermentable glucose from bioconversion of cellulose using efficient microbial cellulases produced from water hyacinth waste

The economic production of cellulase enzymes for various industrial applications is one of the major research areas. A number of broad industrial applications, for example, in cellulosic biomass hydrolysis for simple sugars such as glucose and subsequent biofuel production, make these enzyme systems the third most demanding enzymes. Nevertheless, due to their production on commercial substrates, cellulases fall into the category of costly enzymes. Therefore, the goal of the present work is to evaluate the enhancement of cellulase production and its utilization in the enzymatic hydrolysis of biomass using low-cost cellulosic substrate, which is abundant and widely available. In this context, waste biomasses of water hyacinth (WH), including leaves and stems, have been used as feedstock to produce cellulases via solid-state fermentation (SSF) in the current study, which improves its production as well as activity. Furthermore, the impact of process parameters like temperature and pH has been investigated for improved cellulase production. At optimum concentration using 10 g of feedstock, 22 IU/gds of FP, 92 IU/gds of BGL, and 111 IU/gds of EG have been noticed in day 5 of SSF. Herein, 40 °C has been identified as the optimum temperature for cellulase production, whereas 50-55 °C has been recorded as the optimum reaction temperature for cellulase enzyme activity. Additionally, pH 5.5 has been identified as the optimum pH for cellulase enzyme production, whereas this enzyme was thermally stable (55 °C) at pH 5.0 up to 3.5 h. Further, the cellulosic biomass hydrolysis of WH leaves via an optimized crude enzyme has been performed, and this could release 24.34 g/L of glucose in 24 h of the reaction. The current findings may have potential for developing cellulases for mass-scale production using WH-based waste bioresources for numerous biorefinery applications.

Primary Sludge from Dairy and Meat Processing Wastewater and Waste from Biomass Enzymatic Hydrolysis as Resources in Anaerobic Digestion and Co-Digestion Supplemented with Biodegradable Surfactants as Process Enhancers

Incorporation of various alternative resources as co-digestion substrates aids to reduce the consumption of agricultural crops for biogas production. However, the efficiency and limitations of these co-substrates is still not fully understood. Use of biomass waste remaining after enzymatic hydrolysis for high value chemical fermentation, meat processing and dairy wastewater primary sludge as co-substrates in an agricultural resource anaerobic digestion plant is tackled within this study. The results showed that anionic surfactants (<200 ppm) can be used to improve fat, oil and grease (FOG) solubility in water and, at the same time, enhance the biomethane potential of FOG-containing sludge by increasing it from 1374.5 to 1765 mLCH4/gVS for meat processing wastewater primary sludge, and from 534 to 740 mLCH4/gVS for dairy wastewater primary sludge, when agricultural digestate is used as a substrate and sludge loading is not more than 10% from the volatile solids loaded. At the same time, only 549.7 mLCH4/gVS was produced as 30-day BMP when 5% biomass hydrolysis waste was used. Biomass hydrolysis waste co-digestion with primary sludge from dairy and meat processing wastewaters has an antigenic effect, and separate substrate anaerobic digestion gave a better results, thus, showing that excessive combination of various waste resources can be inhibitory for biogas production and the appropriate substrate selection and combination is a technical challenge for the biogas industry.

Advances and Challenges in Biocatalysts Application for High Solid-Loading of Biomass for 2nd Generation Bio-Ethanol Production

Growth in population and thereby increased industrialization to meet its requirement, has elevated significantly the demand for energy resources. Depletion of fossil fuel and environmental sustainability issues encouraged the exploration of alternative renewable eco-friendly fuel resources. Among major alternative fuels, bio-ethanol produced from lignocellulosic biomass is the most popular one. Lignocellulosic biomass is the most abundant renewable resource which is ubiquitous on our planet. All the plant biomass is lignocellulosic which is composed of cellulose, hemicellulose and lignin, intricately linked to each other. Filamentous fungi are known to secrete a plethora of biomass hydrolyzing enzymes. Mostly these enzymes are inducible, hence the fungi secrete them economically which causes challenges in their hyperproduction. Biomass’s complicated structure also throws challenges for which pre-treatments of biomass are necessary to make the biomass amorphous to be accessible for the enzymes to act on it. The enzymatic hydrolysis of biomass is the most sustainable way for fermentable sugar generation to convert into ethanol. To have sufficient ethanol concentration in the broth for efficient distillation, high solid loading >20% of biomass is desirable and is the crux of the whole technology. High solid loading offers several benefits including a high concentration of sugars in broth, low equipment sizing, saving cost on infrastructure, etc. Along with the benefits, several challenges also emerged simultaneously, like issues of mass transfer, low reaction rate due to water constrains in, high inhibitor concentration, non-productive binding of enzyme lignin, etc. This article will give an insight into the challenges for cellulase action on cellulosic biomass at a high solid loading of biomass and its probable solutions.

Correlation between physicochemical characteristics of lignin deposited on autohydrolyzed wood chips and their cellulase enzymatic hydrolysis

Enzymatic hydrolysis is a method to generate biofuel from biomass, and autohydrolysis is a popular method to pretreat biomass prior to enzymatic hydrolysis. The primary aim of the present study was to determine the role of lignin produced in the autohydrolysis process on the enzymatic hydrolysis of biomass. The HSQC and 31P NMR analyses confirmed that β-O-4 of lignin was reduced, while β-5, β-β, and S/G-ratio of lignin were increased with intensifying the hydrolysis intensity.The increase in the hydrolysis intensity significantly enhanced the condensed and non-condensed phenolic OH group of lignin. Interestingly, the cellulase enzyme adsorbed more on lignin that had more phenolic content, and its association with lignin reduced its activity for hydrolyzing cellulose microcrystals. Strong negative correlations were observed between the enzymatic hydrolysis yield and the condensed S-OH (r2 = 0.978) and G-OH (r2 = 0.961) of lignin generated in the autohydrolysis process.

Production of Fermentable Sugars from Cassava Stem using Hybrid Pretreatment Technology

One of the crucial steps in the enzymatic hydrolysis of biomass is pretreatment. We investigated the applicability of a hybrid pretreatment method, This involved acid treatment followed by alkali before the production of fermentable sugars from cassava stem. The substrate was initially treated with acid (1% oxalic acid at 100 °C for 2 h), followed by treatment with a 10% NaOH–urea mixture (by mixing 5 g each of NaOH and urea in 100 mL of water) at 100 °C for 1 h. A cellulose recovery of 98.55% was obtained with the acid-alkali pretreatment method.

Direct observation of endoglucanase fibrillation and rapid thickness identification of cellulose nanoplatelets using constructive interference

Better understanding through direct observation of the mechanisms involved in chemical and enzymatic hydrolysis of biomass is of great importance, to implement a substitute for the common cellulose standards. We report the hydrolysis of biomass, using exclusively the parenchyma, to isolate cellulose nanoplatelets using a less harsh pretreatment. Then, we show direct evidence of the effect of endoglucanase on the structure of cellulose nanoplatelets, finding that amorphous cellulose is exclusively digested, loosening the cellulose nanofibrils in the process. The analysis of micrographs demonstrates that when cellulose nanoplatelets are deposited on a silicon wafer, its thickness can be qualitatively measured by the interference color detected using an optical microscope. This finding facilitates further studies of mechanisms involved in lignin removal and cellulose nanofibrils production by specific enzymatic digestion.

Recycling of Chrysoporthe cubensis enzymes to overcome the adsorption in lignin and to improve sugarcane bagasse saccharification

Biomass enzymatic hydrolysis efficiency shows some limitations, such as the non-specific adsorption of enzymes in lignin. We evaluated the adsorption of proteins and enzymes from Chrysoporthe cubensis into alkaline and acid pretreated sugarcane bagasse, containing 8.1 and 33.8% of lignin, respectively. The data from Langmuir isotherm showed that at 4 °C, proteins were more adsorbed by acid-treated bagasse, 10.5 mg g−1, while higher adsorption affinity, 2.0 mL mg−1, was determined from alkali-treated bagasse. Similarly, under hydrolytic conditions (50 °C), higher amounts of proteins were adsorbed into acid-treated bagasse, confirming the predominant effect of lignin on protein adsorption. Enzymatic recycling rounds during alkali-treated bagasse saccharification showed that the addition of fresh substrate and enzymes promoted the higher release of glucose and xylose, 40.3 and 38.3 g L−1, respectively. However, the addition of only fresh substrates showed to be efficient for C. cubensis enzymes recovery and substrate hydrolysis, which reduces enzyme consumption and costs.

IMPROVEMENT OF BIOETHANOL PRODUCTION FROM LOW GRADE AND DAMAGED LONGAN FRUITS WITH THERMAL PRETREATMENT AND DIFFERENT TYPES OF THE ENZYMATIC HYDROLYSIS

Pretreatment is a vital step in the enzymatic hydrolysis of biomass and the successive production of bioethanol. The present study is focused on thermal pretreatment (boiling & autoclave) methods of low grade and damaged longan fruits using three different types of the enzymatic sources from commercial cellulase, an enzyme from algae and mixed enzymes (i.e., commercial cellulase with algal enzyme). Total sugar production after the hydrolysis process from commercial cellulase, the enzyme from algae and mixed enzymes were 326.41 ± 08.97 g/L, 348.68 ± 01.95 g/L and 368.42 ± 01.16 g/L, respectively. Reducing sugar after the hydrolysis process generated from commercial cellulase, the enzyme from algae and mixed enzymes was 182.54 ± 03.05 g/L, 183.33 ± 04.70 g/L and 297.78 ± 02.94 g/L, respectively. Fermentation of these hydrolysate using Saccharomyces cerevisiae TISTR 5020 produced the highest ethanol production from using commercial cellulase, the enzyme from algae and mixed enzymes was 16.74 ± 0.62 g/L, 5.38 ± 0.54 g/L and 14.32 ± 1.89 g/L, respectively. Consequently, this study suggested that suitable pretreatment and hydrolysis processes are performing a significant role in bioethanol production from low grade and damaged longan fruits.

Cultivation of Microalgae in Media Added of Emergent Pollutants and Effect on Growth, Chemical Composition, and Use of Biomass to Enzymatic Hydrolysis

The objective of this study was to determine the influence of various concentrations of emerging pollutants (EPs) on growth, cell composition, and enzymatic hydrolysis of biomass. The microalgae used were Spirulina platensis LEB-52, Chlorella homosphaera, and Scenedesmus obliquus. The EPs used were paracetamol, diazepam, fluoxetine, acetylsalicylic acid, and caffeine, added to the cultures in concentrations ranging from 1 to 100 mg L−1. The tests were carried out in closed 150-mL Erlenmeyer bioreactors, containing standard medium from each microalga culture. Cell concentrations were determined every 24 h using optical density. Culture continued for 20 days. At the end of the growth, biomass was collected and used to measure carbohydrates, proteins, and enzymatic hydrolysis, to determine possible changes due to the presence of EPs. In general, microalgae resisted concentrations of up to 100 mg L−1 of paracetamol, acetylsalicylic acid, and caffeine, 30 mg L−1 of diazepam, and 1 mg L−1 of fluoxetine. S. obliquus was the most resistant strain, followed by C. homosphaera and S. platensis LEB-52 being less resistant. Acetylsalicylic acid and caffeine influenced the content of carbohydrates and proteins in biomass, reaching values ​above 35% of carbohydrates for S. platensis LEB-52 and above 66% of proteins for S. obliquus. There was no influence of EPs in the enzymatic hydrolysis processes. Microalgae showed resistance to EP concentrations, thereby emerging as a promising wastewater bioremediation technology. These high levels of carbohydrates are of great value because they can be used in the production of bioethanol.

Modeling of optimal green liquor pretreatment for enhanced biomass saccharification and delignification by distinct alteration of wall polymer features and biomass porosity in Miscanthus

Abstract Miscanthus is a leading bioenergy crop with enormous biomass resource convertible into bioethanol and biochemicals. However, lignocellulose recalcitrance basically causes costly bioethanol production with potential secondary pollution to the environment. In this study, the green liquor (mixed sodium carbonate and sodium sulfide) pretreatments were optimized using response surface methodological modeling for enhancing biomass saccharification and delignification in Miscanthus. By comparison, the optimal saccharification approach led to relatively higher hexose yield of 87% (% cellulose) for bioethanol yield of 17.1% (% dry matter) with the sugar-ethanol conversion rate at 98%, whereas the optimal delignification approach could achieve the highest delignification rate at 93% potential for lignin-derived biofuel or value-added biochemicals. Notably, those two optimized pretreatments could distinctively extract hemicellulose-lignin complex and altered wall polymer features, leading to much increased cellulose accessibility for efficient biomass enzymatic hydrolysis. Exceptionally, the optimal delignification led to decreased biomass porosity accountable for relatively lower hexose yield, suggesting that its cellulose microfibrils may be aggregated from excessive non-cellulosic polymers extraction. Hence, this study has demonstrated two optional strategies for green-like and cost-effective biofuels and biochemical production in Miscanthus and other bioenergy crops.

Distinct mechanisms of enzymatic saccharification and bioethanol conversion enhancement by three surfactants under steam explosion and mild chemical pretreatments in bioenergy Miscanthus

Miscanthus is a leading bioenergy crop that represents an enormous lignocellulose resource for biofuels and bioproducts. However, as lignocellulose recalcitrance leads to financially inviable bioethanol production and the potential of secondary wastes into the environment, it becomes crucial to explore green-like and cost-effective biomass processing technologies. To address these issues, low doses of chemical surfactants have been added to enhance biomass enzymatic hydrolysis and bioethanol conversion, but much remains unknown about the mechanism of enhancement. For first time, in this study, a novel chemical surfactant (1% Silwet L-77) was applied to enhance the enzymatic hydrolysis of raw Miscanthus straw, and 40% cellulose digestion was achieved, which is 1.2- and 4.5-fold higher than that of two well-known surfactants (PEG-4000 and Tween-80), respectively. Using lignocellulose substrates obtained from Miscanthus biomass samples that were pretreated by green-like steam explosion followed by mild chemical (NaOH or H2SO4) pretreatments, supplementation with the three surfactants led to significantly enhanced enzymatic saccharification. The 2% Tween-80 supply resulted in a hexose yield of 99% (% cellulose) from enzymatic hydrolysis, followed by 95% with 0.5% PEG-4000 and 71% with 1% Silwet L-77. Despite the slightly lower hexose yield, Silwet L-77 resulted in consistently higher sugar-ethanol conversion rates in all lignocellulose substrates examined. Furthermore, based on the enzyme profiling of mixed cellulase adsorption on lignocellulose and the chemical analysis of wall polymer features and lignocellulose accessibility, this study proposed multiple hypothetical models to interpret the distinct enhancement roles of three surfactants in the enzymatic hydrolyses of diverse lignocellulose substrates. These models also provide a powerful strategy for low-cost bioethanol production with the potential for high-value bioproducts by using desirable surfactants in Miscanthus and other bioenergy crops.

High-temperature tolerant enzyme based extraction of lignocellulose derived C5 and C6 sugars for the integrated production of a promising supplement for a diesel/jet-engine fuel

Development of a novel, integrated production of C8 ester butyl butyrate (BuB), a promising supplement for diesel/jet-engine fuels, from lignocellulose derived C5 and C6 sugars is attempted by means of smart and innovative process design. In the pathway, enzymatic hydrolysis of biomass with high solid loading is an important step which requires reduced amount of water supply and energy input. However, increased substrate loading lead to diffusion limitations of enzymes, on top of nonproductive absorption of enzymes. Addition of ß-glucosidase over cellulase is another reason to increase the cost of enzymes. Viscozyme can be considered as a troubleshooter in these cases where it can offset high substrate loading and increased monomeric sugar generation. In the present study, 17.61 g/L of glucose, along with 7.43 g/L of xylose, have been recovered with a viscozyme concentration of 54.4 g/L. Additionally, thermal deactivation of viscozyme has been investigated. The deactivation constant is found to be gradually increasing with escalated enzyme loading from 24.2 g/L to 54.4 g/L. In this study, it has been found that hydrolysis of biomass follows a first order pseudo-kinetics and the same is eventually used to determine the fractal kinetics of cellulose hydrolysis. Fractal kinetics showed that increment of enzyme concentration is associated with lower fractal dimensions and increased binding capacity of substrate and enzyme. Diffusion limitation of the present enzyme-substrate system has also been investigated. It is observed that faster diffusion, along with increased resistances, can be achieved with increased enzyme concentration.

Combined bead milling and enzymatic hydrolysis for efficient fractionation of lipids, proteins, and carbohydrates of Chlorella vulgaris microalgae

A combined bead milling and enzymatic hydrolysis process was developed for fractionation of the major valuable biomass components, i.e., proteins, carbohydrates, and lipids from the microalgae Chlorella vulgaris. The cells were treated by bead milling followed by hydrolysis with different hydrolytic enzymes, including lipase, phospholipase, protease, and cellulase. Without enzymatic hydrolysis, the recovery yield of lipids, carbohydrates, and proteins for bead milled biomass was 75%, 31%, and 40%, respectively, while by applying enzymatic treatments these results were improved significantly. The maximum recovery yield for all components was obtained after enzymatic hydrolysis of bead milled biomass by lipase at 37 °C and pH 7.4 for 24 h, yielding 88% lipids in the solid phase while 74% carbohydrate and 68% protein were separated in the liquid phase. The recovery yield of components after enzymatic hydrolysis of biomass without bead milling was 44% lower than that of the milled biomass.

Estimation of Biomass Enzymatic Hydrolysis State in Stirred Tank Reactor through Moving Horizon Algorithms with Fixed and Dynamic Fuzzy Weights

Second generation ethanol faces challenges before profitable implementation. Biomass hydrolysis is one of the bottlenecks, especially when this process occurs at high solids loading and with enzymatic catalysts. Under this setting, kinetic modeling and reaction monitoring are hindered due to the conditions of the medium, while increasing the mixing power. An algorithm that addresses these challenges might improve the reactor performance. In this work, a soft sensor that is based on agitation power measurements that uses an Artificial Neural Network (ANN) as an internal model is proposed in order to predict free carbohydrates concentrations. The developed soft sensor is used in a Moving Horizon Estimator (MHE) algorithm to improve the prediction of state variables during biomass hydrolysis. The algorithm is developed and used for batch and fed-batch hydrolysis experimental runs. An alteration of the classical MHE is proposed for improving prediction, using a novel fuzzy rule to alter the filter weights online. This alteration improved the prediction when compared to the original MHE in both training data sets (tracking error decreased 13%) and in test data sets, where the error reduction obtained is 44%.

A novel environmentally friendly process for depolymerization of hydrolysis lignin using Kraft cooking liquor: chemicals recoverable by the Kraft recovery cycle

AbstractHydrolysis lignin (HL) refers to a lignin‐rich residue obtained after the enzymatic hydrolysis of biomass. It is recalcitrant, heterogeneous, insoluble in most common solvents, and less reactive than other lignins. To enhance the reactivity of HL, a novel environmentally friendly depolymerization approach was demonstrated to produce depolymerized hydrolysis lignin (DHL) using Kraft cooking liquor, white liquor (WL) – recoverable by the Kraft recovery cycle. The effects of various process parameters such as reaction time, WL/HL ratio, and reaction temperature on lignin depolymerization were investigated using a 2 L Parr reactor under N2. The DHLs obtained were then characterized by Gel permeation chromatography (GPC)‐Ultraviolet Detector (GPC‐UV), 31P Nuclear Magnetic Resonance (NMR) spectroscopy, and ultraviolet visible (UV–visible) spectroscopy, while the filtrates were characterized by high‐performance liquid chromatography (HPLC) for saccharinic acids. The DHL yield reached 45–70% from the treatments at 150–190 °C for 1 h at a WL/HL mass ratio of 1:4 ~ 2:1. The weight‐average molecular weight (Mw) value of the DHL obtained at 190 °C after treatment for 1 h at a WL/HL ratio of 2:1 (w/w) was 2600 Da. Moreover, a significant increase in non‐condensed phenolic hydroxyl and carboxylic acid group content was observed with decreasing Mw. Compared with various existing lignin modification approaches, the approach reported here is less expensive and more environmentally friendly if integrated into Kraft pulp mill operations with the residual WL from the lignin depolymerization process being recycled to the mill chemical recovery cycle. Process scale‐up was also demonstrated using a 20 L circulating reactor. In this case, the Mw of the DHL produced after treatment at 170 °C for 2 h was 2400 Da. © 2020 Society of Chemical Industry and John Wiley & Sons, Ltd.

Quantification of morphochemical changes during in situ enzymatic hydrolysis of individual biomass particles based on autofluorescence imaging.

Enzymatic hydrolysis of biomass is an established method for producing biofuels. Lignocellulosic biomass such as corn stover is very inhomogeneous material with big variation on conversion rates between individual particles therefore leading to variable recalcitrance results. In this study, we used noninvasive optical microscopy techniques, such as two‐photon microscopy and fluorescence lifetime imaging microscopy, to visualize and analyze morphological and chemical changes of individual corn stover particles pretreated with sulfuric acid during hydrolysis. Morphochemical changes were interpreted based on the fluorescence properties of isolated building blocks of plant cell wall, such as cellulose, hemicellulose, and lignin. Enzymatic hydrolysis resulted in particle size reduction, side wall collapse, decrease of second harmonic signal from cellulose, redshifting of autofluorescence emission, and lifetime decrease attributed to the relative increase of lignin. Based on these observations, tracking compositional change after hydrolysis of individual particles was accomplished. The methodologies developed offer a paradigm for imaging and analyzing enzymatic hydrolysis in vitro and in situ, which could be used for screening enzymes cocktails targeting specific recalcitrant structures or investigating locally enzyme anti‐inhibitory agents.

Assessment of wasteland derived biomass for bioethanol production

Abstract Background The bioethanol produced from biomass is a promising alternative fuel. The lignocellulose from marginal areas or wasteland could be a promising raw material for bioethanol production because it is present in large quantities, is cheap, renewable and has favorable environmental properties. Despite these advantages, lignocellulosic biomass is much more difficult to process than cereal grains, due to the need for intensive pretreatment and relatively large amounts of cellulases for efficient hydrolysis. Therefore, there is a need to develop an efficient and cost-effective method for the degradation and fermentation of lignocellulosic biomass to ethanol. Results The usefulness of lignocellulosic biomass from wasteland for the production of bioethanol using pretreatment with the aid of ionic liquids of 1-ethyl-3-methylimidazolium acetate and 1-ethyl-3-methylimidazolium chloride was evaluated in this study. The pretreatment process, enzymatic hydrolysis and alcoholic fermentation lasted a total of 10 d. The largest amounts of bioethanol were obtained from biomass originating from agricultural wasteland, in which the dominant plant was fireweed (Chamaenerion angustifolium) and from the field where the common broom (Cytisus scoparius) was the dominant. Conclusions The plants such as fireweed, common broom, hay and goldenrod may be useful for the production of liquid biofuels and it would be necessary in the further stage of research to establish and optimize the conditions for the technology of ethyl alcohol producing from these plant species. Enzymatic hydrolysis of biomass from agricultural wastelands results in a large increase in fermentable sugars, comparable to the enzymatic hydrolysis of rye, wheat, rice or maize straw. How to cite: Smuga-Kogut M, Piskier T, Walendzik B, et al. Assessment of wasteland derived biomass for bioethanol production. Electron J Biotechnol 2019;41. https://doi.org/10.1016/j.ejbt.2019.05.001.

A finalized determinant for complete lignocellulose enzymatic saccharification potential to maximize bioethanol production in bioenergy Miscanthus

BackgroundMiscanthus is a leading bioenergy crop with enormous lignocellulose production potential for biofuels and chemicals. However, lignocellulose recalcitrance leads to biomass process difficulty for an efficient bioethanol production. Hence, it becomes essential to identify the integrative impact of lignocellulose recalcitrant factors on cellulose accessibility for biomass enzymatic hydrolysis. In this study, we analyzed four typical pairs of Miscanthus accessions that showed distinct cell wall compositions and sorted out three major factors that affected biomass saccharification for maximum bioethanol production.ResultsAmong the three optimal (i.e., liquid hot water, H2SO4 and NaOH) pretreatments performed, mild alkali pretreatment (4% NaOH at 50 °C) led to almost complete biomass saccharification when 1% Tween-80 was co-supplied into enzymatic hydrolysis in the desirable Miscanthus accessions. Consequently, the highest bioethanol yields were obtained at 19% (% dry matter) from yeast fermentation, with much higher sugar–ethanol conversion rates by 94–98%, compared to the other Miscanthus species subjected to stronger pretreatments as reported in previous studies. By comparison, three optimized pretreatments distinctively extracted wall polymers and specifically altered polymer features and inter-linkage styles, but the alkali pretreatment caused much increased biomass porosity than that of the other pretreatments. Based on integrative analyses, excellent equations were generated to precisely estimate hexoses and ethanol yields under various pretreatments and a hypothetical model was proposed to outline an integrative impact on biomass saccharification and bioethanol production subjective to a predominate factor (CR stain) of biomass porosity and four additional minor factors (DY stain, cellulose DP, hemicellulose X/A, lignin G-monomer).ConclusionUsing four pairs of Miscanthus samples with distinct cell wall composition and varied biomass saccharification, this study has determined three main factors of lignocellulose recalcitrance that could be significantly reduced for much-increased biomass porosity upon optimal pretreatments. It has also established a novel standard that should be applicable to judge any types of biomass process technology for high biofuel production in distinct lignocellulose substrates. Hence, this study provides a potential strategy for precise genetic modification of lignocellulose in all bioenergy crops.

Pretreatment of Eucalyptus urophylla in γ-valerolactone/dilute acid system for removal of non-cellulosic components and acceleration of enzymatic hydrolysis

Enzymatic hydrolysis of biomass is highly dependent on the changes in chemical compositions and structural characteristics after pretreatment. γ-Valerolactone (GVL)/dilute acid pretreatment is an effective approach to remove hemicelluloses and lignin and disrupt the cell wall structure, leading to the improvement of enzymatic hydrolysis. This study examined the influence of chemical compositions and structural features on the enzymatic hydrolysis of Eucalyptus urophylla from GVL/dilute acid pretreatment. Results revealed that glucose yield showed a positive correlation with removal rate of hemicelluloses and lignin. Particularly, there was no direct correlation of cellulose crystallinity on enzymatic hydrolysis. The highest glucose yield of 89.1% was achieved when the pretreatment was performed with GVL/H2O solution (4:1, v/v) containing 100 mM H2SO4 at 120 °C for 60 min. Meanwhile, under the mentioned conditions, 16.5% of lignin with a high purity (only contained 0.09% sugars) and molecular weight (3450 g/mol) was fractionated, which can be served as feedstock for future utilization. In short, an extensive understanding of the pretreated biomass and the obtained lignin during the GVL/dilute acid pretreatment will be beneficial for value-added applications of biomass.