Autohydrolysis of Miscanthus x giganteus for the production of xylooligosaccharides (XOS): kinetics, characterization and recovery

Efficient production of xylooligosaccharides from Camellia oleifera shells pretreated by pyruvic acid at lower temperature

XOS production from lignocellulose using organic carboxylic acids and alkyd acids has been widely reported. However, it still faces harsh challenges such as high energy consumption, high cost, and low purity. Pyruvic acid (PYA), a carbonyl acid with carbonyl and carboxyl groups, was used to produce XOS due to its stronger catalytic activity. In this work, XOS was efficiently prepared from COS in an autoclave under the condition of 0.21 M PYA-121 °C-35 min. The total yield of XOS reached 68.72 % without producing any toxic by-products, including furfural (FF) and 5-hydroxymethylfurfural (5-HMF). The yield of xylobiose (X2), xylotriose (X3), xylotetraose (X4), and xylopentaose (X5) were 20.58 %, 12.47 %, 15.74 %, and 10.05 %, respectively. Meanwhile, 89.05 % of lignin was retained in the solid residue, which provides a crucial functional group for synthesizing layered carbon materials (SRG-a). It achieves excellent electromagnetic shielding (EMS) performance through graphitization, reaching -30 dB at a thickness of 2.0 mm. The use of a PYA catalyst in the production of XOS has proven to be an efficient method due to lower temperature, lower acid consumption, and straightforward operation.

Recent Advances in Miscanthus Macromolecule Conversion: A Brief Overview

Miscanthus is a valuable renewable feedstock and has a significant potential for the manufacture of diverse biotechnology products based on macromolecules such as cellulose, hemicelluloses and lignin. Herein, we overviewed the state-of-the art of research on the conversion of miscanthus polymers into biotechnology products comprising low-molecular compounds and macromolecules: bioethanol, biogas, bacterial cellulose, enzymes (cellulases, laccases), lactic acid, lipids, fumaric acid and polyhydroxyalkanoates. The present review aims to assess the potential of converting miscanthus polymers in order to develop sustainable technologies.

Effects of Hydrothermal Processing on Miscanthus × giganteus Polysaccharides: A Kinetic Assessment

Miscanthus × giganteus samples were characterized for composition and treated with hot compressed water (hydrothermal or autohydrolysis treatments) at temperatures in the range of 190-240 °C. The liquid phases from treatments were analyzed to assess the breakdown of susceptible polysaccharides into a scope of soluble intermediates and reaction products. The experimental concentration profiles determined for the target compounds (monosaccharides, higher saccharides, acetic acid and sugar-decomposition products) were interpreted using a pseudohomogeneous kinetic mechanism involving 27 reactions, which were governed by kinetic coefficients showing an Arrhenius-type temperature dependence. The corresponding activation energies were calculated and compared with data from the literature. The kinetic equations allowed a quantitative assessment of the experimental results, providing key information for process simulation and evaluation.

Preparation and nutritional properties of xylooligosaccharide from agricultural and forestry byproducts: A comprehensive review

Xylooligosaccharide (XOS) are functional oligosaccharides with prebiotic activities, which originate from lignocellulosic biomass and have attracted extensive attention from scholars in recent years. This paper summarizes the strategies used in the production of XOS, and introduces the raw materials, preparation methods, and purification technology of XOS. In addition, the biological characteristics and applications of XOS are also presented. The most commonly recommended XOS production strategy is the two-stage method of alkaline pre-treatment and enzymatic hydrolysis; and further purification by membrane filtration to achieve the high yield of XOS is required for prebiotic function. At the same time, new strategies and technologies such as the hydrothermal and steam explosion have been used as pre-treatment methods combined with enzymatic hydrolysis to prepare XOS. XOS have many critical physiological activities, especially in regulating blood glucose, reducing blood lipid, and improving the structure of host intestinal flora.

Production of Xylooligosaccharides from Jiuzao by Autohydrolysis Coupled with Enzymatic Hydrolysis Using a Thermostable Xylanase

The production of xylooligosaccharides (XOS) from Jiuzao was studied using a two-stage process based on autohydrolysis pretreatment followed by enzymatic hydrolysis. Jiuzao was autohydrolyzed under conditions where temperature, time, particle size, and solid-liquid ratio were varied experimentally. Optimal XOS production was obtained from Jiuzao with a >20 mesh particle size treated at 181.5 °C for 20 min with a 1:13.6 solid-liquid ratio. Subsequently, optimal enzymatic hydrolysis conditions for xylanase XynAR were identified as 60 °C, pH 5, and xylanase XynAR loading of 15 U/mL. Using these conditions, a yield of 34.2% XOS was obtained from Jiuzao within 2 h. The process developed in the present study could enable effective and ecofriendly industrial production of XOS from Jiuzao.

Functional properties of miscanthus fiber and prebiotic blends in extruded canine diets

Dietary fiber has become increasingly recognized as a key factor in maintaining gastrointestinal health. Dietary fiber sources are often comprised of several different fiber fractions, each with unique physicochemical properties. These properties can have varying physiological effects on the gastrointestinal tract that include modulation of microbiota, production of fermentation-derived metabolites, and laxation. The objectives of this study were 1) to determine the effects of a novel dietary fiber source, miscanthus grass fiber (MF), and prebiotic and fiber blends on gastrointestinal tolerance, apparent total tract digestibility, fecal metabolites, and fecal microbiota and 2) to evaluate the palatability of extruded diets containing MF in comparison to traditional dietary fiber sources. All animal procedures were approved by the University of Illinois Institutional Animal Care and Use Committee. Six dietary treatments were formulated to meet or exceed the AAFCO nutrient profile of 2018 and included either cellulose (CO), beet pulp (BP), MF, or a blend of MF and tomato pomace, MF and resistant starch, or MF and fructooligosaccharide. A total of 12 adult neutered female beagles (mean age 5.8 ± 1.1 yr; mean body weight 10.9 ± 1.0 kg; mean body condition score 5.7 ± 0.7) were randomly assigned to one of the six treatment diets in a replicated 6 × 6 Latin square design. Each dog was fed their assigned diet for a treatment period of 21 d with 17 d of diet adaptation followed by 4 d of total and fresh fecal collection. All diets were well accepted and digested by the dogs. Dogs fed BP had greater fecal total short-chain fatty acid concentration than the CO treatment (P < 0.05), while the dogs fed diets containing MF were intermediate. In a two-bowl palatability trial, no significant preference was observed between the extruded diets containing MF and CO (P > 0.05). However, a significant preference for the extruded diet containing BP over the diet containing only MF was observed (P < 0.05). The α-diversity of fecal microbial communities was not impacted by treatment (P > 0.05), but β-diversity indicated that dogs fed the BP diet differed from the other treatment groups (P < 0.05). The data from this study suggest that miscanthus grass can be successfully utilized in fiber blends in extruded diets for adult dogs, with modulatory effects similar to the traditional dietary fiber source, cellulose.

Hydrothermal pretreatment for valorization of genetically engineered bioenergy crop for lipid and cellulosic sugar recovery

Lipids accumulated in the vegetative tissues of cellulosic feedstocks can be a potential raw material for biodiesel and bioethanol production. In this work, bagasse of genetically engineered sorghum was subjected to liquid hot-water pretreatment at 170, 180, and 190 °C for different reaction time. Under the optimal pretreatment condition (170 °C, 20 min), the residue was enriched in glucan (57.39 ± 2.63 % w/w) and xylan (13.38 ± 0.49 % w/w). The total lipid content of the pretreated residue was 6.81% w/w, similar to that observed in untreated bagasse (6.30% w/w). Pretreatment improved the enzymatic digestibility of bagasse, allowing a recovery of 79% w/w and 86% w/w of glucose and xylose, respectively. The pretreatment and enzymatic saccharification resulted in a 2-fold increase in total lipid in enzymatic residue compared to the original bagasse. Thus, pretreatment and enzymatic hydrolysis enabled high sugar recovery while concentrating triglycerides and free fatty acids in the residue.

Efficient production of xylooligosaccharides rich in xylobiose and xylotriose from poplar by hydrothermal pretreatment coupled with post-enzymatic hydrolysis

A promising approach for production of value-added xylooligosaccharides (XOS) from poplar was developed by combining hydrothermal pretreatment and endo-xylanase post-hydrolysis. Results showed that the 35.4% XOS (DP 2-6) and 17.6% low DP xylans (DP > 6) were obtained at the identified optimal condition (170 °C, 50 min) for hydrothermal pretreatment. Structural features of low DP xylans generated during the hydrothermal pretreatment were examined, revealing that low DP xylans are mainly comprised of 4-O-methylglucuronic xylan and are involved in lignin carbohydrate complexes. Moreover, higher pretreatment intensity promoted the cleavage of side-chain substituents including arabinose and glucuronic acid groups. The subsequent endo-xylanase hydrolysis of the pretreatment liquor hydrolyzed low DP xylans, contributing to a significant improvement in xylobiose and xylotriose proportions. This combined strategy resulted in a XOS with conversion yield of 44.6% containing 78.7% xylobiose and xylotriose starting from the initial xylan in raw poplar.

Techno-economic analysis of producing xylo-oligosaccharides and cellulose microfibers from lignocellulosic biomass

This study assesses the economic performance of a biorefinery producing xylo-oligosaccharides (XOS) from miscanthus by autohydrolysis and purification based on a rigorous model developed in ASPEN Plus. Varied biorefinery capacities (50-250 oven dry metric ton (ODMT)/day) and three XOS content levels (80%, 90%, 95%) are analyzed. The XOS minimum selling price (XOS MSP) is varied between $3,430-$7,500, $4,030-$8,970, and $4,840-$10,640 per metric ton (MT) for 80%, 90%, and 95% content, respectively. The results show that increasing biorefinery capacity can significantly reduce the XOS MSP and higher purity leads to higher XOS MSP due to less yield, and higher capital and operating costs. This study also explores another system configuration to produce high-value byproducts, cellulose microfiber, by utilizing the cellulose to produce microfiber instead of combusting for energy recovery. The XOS MSP of cellulose microfiber case is $2,460-$7,040/MT and thus exhibits potential economic benefits over the other cases.

Improving the catalytic performance of xylanase from Bacillus circulans through structure-based rational design

Endo-1,4-β-xylanase is one of the most important enzymes employed in biorefineries for obtaining fermentable sugars from hemicellulosic components. Herein, we aimed to improve the catalytic performance of Bacillus circulans xylanase (Bcx) using a structure-guided rational design. A systematic analysis of flexible motions revealed that the R49 component of Bcx (i) constrains the global conformational changes essential for substrate binding and (ii) is involved in modulating flexible motion. Site-saturated mutagenesis of the R49 residue led to the engineering of the active mutants with the trade-off between flexibility and rigidity. The most active mutant R49N improved the catalytic performance, including its catalytic efficiency (7.51-fold), conformational stability (0.7 °C improvement), and production of xylose oligomers (2.18-fold higher xylobiose and 1.72-fold higher xylotriose). The results discussed herein can be applied to enhance the catalytic performance of industrially important enzymes by controlling flexibility.

Two-stage processing for xylooligosaccharide recovery from rice by-products and evaluation of products: Promotion of lactic acid-producing bacterial growth and food application in a high-pressure process

In this study, we attempted to maximize arabinoxylan conversion into xylooligosaccharide (XOS) from rice husk and rice straw using two saccharification processes and evaluate the promotion of lactic acid-producing bacterial growth, including an investigation of the role of prebiotics in protecting probiotic bacteria in rice drink products in a high-pressure process (HPP). Hydrothermal treatment followed by enzymatic hydrolysis was designed for XOS recovery from rice husk arabinoxylan (RH-AX) and rice straw arabinoxylan (RS-AX). The hydrothermal treatment performed at 170 °C for 20 min and 180 °C for 10 min was the optimal condition to produce XOS liquor from rice husk and rice straw, respectively. Pentopan mono BG successfully recovered XOS from rice husk and rice straw residues at 50 °C, pH 5.5, an enzyme concentration of 50 U and 100 U/g substrate for 24 h. This design converted 92.17 and 88.34% (w/w) of initial RH-AX and RS-AX into saccharides, which comprised 64.01 and 59.52% of the XOS content, respectively. Rice husk xylooligosaccharide (RH-XOS) and rice straw xylooligosaccharide (RS-XOS) had degrees of polymerization ranging from 2 to 6 with some arabino-xylooligosaccharides. RH-XOS and RS-XOS were used to examine the promotion of the growth of lactic acid-producing bacteria strains in the presence of other prebiotics. RH-XOS and RS-XOS strongly promoted the growth of Lactobacillus sakei and Lactobacillus brevis, while other species showed weak to moderate growth. This study represents the first report of the powerful effect of Lactococcus lactis KA-FF1-4 on altering the utilization of XOS but not xylose. Furthermore, for the first time, we reported the capability of XOS to protect probiotics in rice drinks under high-pressure conditions. RH-XOS and RS-XOS resulted in the highest viability of approximately 11 log cfu/mL and exhibited no significant difference compared with the non-HPP treatment. Hence, rice husk and rice straw can be utilized as alternative prebiotic sources that provide biological activity and food applications in the HPP industry.

In Situ Chemical Locking of Acetates During Xylo-Oligosaccharide Preparation by Lignocellulose Acidolysis

Xylo-oligosaccharides with high value could be obtained by acidolysis of lignocellulosic biomass with acetic acid, which was an urgent problem to solve for the separation of acetic acid from crude xylo-oligosaccharides solution. Four neutralizers, CaCO₃, CaO, Na₂CO₃, and NaOH, were used for in situ chemically locking the acetic acid in the acidolyzed hydrolysate of corncob. The chemically locked hydrolysate was analyzed and compared using vacuum evaporation and spray drying. After CaCO₃, CaO, Na₂CO₃, and NaOH treatment, the locking rates of acetic acid were 92.62%, 94.89%, 95.05%, and 95.58%, respectively, and 39.55 g, 41.13 g, 41.78 g, and 41.87 g of the compound of xylo-oligosaccharide and acetate were obtained. Sodium neutralizer had lesser effect on xylo-oligosaccharide content, and Na₂CO₃ was the best chemical for locking acetic acid among these four neutralizers. This process provides a novel method for effectively utilizing acetic acid during the industrial production of xylo-oligosaccharides via acetic acid.

Evaluation of Xylooligosaccharides Production for a Specific Degree of Polymerization by Liquid Hot Water Treatment of Tropical Hardwood

Eucalyptus pellita is known as attractive biomass, and it has been utilized for eucalyptus oil, furniture, and pulp and paper production that causes a significant amount of byproducts. Liquid hot water treatment depending on combined severity factor (CSF) was subjected to isolate hemicellulose fraction from E. pellita and to produce xylooligosaccharides (XOS). The xylan extraction ratio based on the initial xylan content of the feedstock was maximized up to 77.6% at 170 °C for 50 min condition (CSF: 1.0), which had accounted for XOS purity of 76.5% based on the total sugar content of the liquid hydrolysate. In this condition, the sum of xylobiose, xylotriose, and xylotetraose which has a low degree of polymerization (DP) of 2 to 4 was determined as 80.6% of the total XOS. The highest XOS production score established using parameters including the xylan extraction ratio, XOS purity, and low DP XOS ratio was 5.7 at CSF 1.0 condition. XOS production score evaluated using the CSF is expected to be used as a productivity indicator of XOS in the industry (R-squared value: 0.92).

Environmentally Friendly Approach for the Production of Glucose and High-Purity Xylooligosaccharides from Edible Biomass Byproducts

Xylooligosaccharides (XOS) production from sweet sorghum bagasse (SSB) has been barely studied using other edible biomasses. Therefore, we evaluated the XOS content as well as its purity by comparing the content of total sugars from SSB. An environmentally friendly approach involving autohydrolysis was employed, and the reaction temperature and time had variations in order to search for the conditions that would yield high-purity XOS. After autohydrolysis, the remaining solid residues, the glucan-rich fraction, were used as substrates to be enzymatically hydrolyzed for glucose conversion. The highest XOS was observed for total sugars (68.7%) at 190 °C for 5 min among the autohydrolysis conditions. However, we also suggested two alternative conditions, 180 °C for 20 min and 190 °C for 15 min, because the former condition might have the XOS at a low degree of polymerization with a high XOS ratio (67.6%), while the latter condition presented a high glucose to total sugar ratio (91.4%) with a moderate level XOS ratio (64.4%). Although it was challenging to conclude on the autohydrolysis conditions required to obtain the best result of XOS content and purity and glucose yield, this study presented approaches that could maximize the desired product from SSB, and additional processes to reduce these differences in conditions may warrant further research.

An integrated approach to obtain xylo-oligosaccharides from sugarcane straw: From lab to pilot scale

Sugarcane straw (SS) is a widely available agricultural processing feedstock with the potential to produce 2nd generation bioethanol and bioproducts, in addition to the more conventional use for heat and/or electrical power generation. In this study, we investigated the operational parameters to maximize the production of xylo-oligosaccharides (XOS) using mild deacetylation, followed by hydrothermal pretreatment. From the laboratory to the pilot-scale, the optimized two-stage pretreatment promoted 81.5% and 70.5% hemicellulose solubilization and led to XOS yields up to 9.8% and 9.1% (w/w of initial straw), respectively. Moreover, different fungal xylanases were also tested to hydrolyze XOS into xylobiose (X2) and xylotriose (X3). GH10 from Aspergillus nidulans performed better than GH11 xylanases and the ratio of the desired products (X2 + X3) increased to 72% due to minimal monomeric sugar formation. Furthermore, a cellulose-rich fraction was obtained, which can be used in other high value-added applications, such as for the production of cello-oligomers.

Production, separation, and characterization of high-purity xylobiose from enzymatic hydrolysis of alkaline oxidation pretreated sugarcane bagasse

The production of high-purity xylobiose from lignocellulose is an expensive and tedious process. In this work, the production of xylobiose from enzymatic hydrolysis of alkaline oxidation pretreated sugarcane bagasse was investigated. Furthermore, a simple process for the separation of xylobiose from enzymatic hydrolysate by activated carbon absorption, water washing, and ethanol-water desorption was developed. Under the optimized separation conditions, 96.77% xylobiose was adsorbed at 16% activated carbon loadings. Moreover, xylose and acetate could not be detected after washing by 3-fold volume of water. Xylobiose with 80.16% yield was eluted by 5-fold volume of 5% (v/v) ethanol-water. The reusability of activated carbon was evaluated by 5 cycles of adsorption-desorption process, suggesting that the activated carbon exhibited good reusability. The separated xylobiose sample with high-purity (97.29%) was confirmed by HPLC, ESI-MS, and NMR. Overall, this study provided a low-cost and robust technology for the production and separation of high-purity xylobiose from lignocellulose.

Pilot-scale production of xylo-oligosaccharides and fermentable sugars from Miscanthus using steam explosion pretreatment

This study investigated pilot-scale production of xylo-oligosaccharides (XOS) and fermentable sugars from Miscanthus using steam explosion (SE) pretreatment. SE conditions (200 °C; 15 bar; 10 min) led to XOS yields up to 52 % (w/w of initial xylan) in the hydrolysate. Liquid chromatography-mass spectrometry demonstrated that the solubilised XOS contained bound acetyl- and hydroxycinnamate residues, physicochemical properties known for high prebiotic effects and anti-oxidant activity in nutraceutical foods. Enzymatic hydrolysis of XOS-rich hydrolysate with commercial endo-xylanases resulted in xylobiose yields of 380 to 500 g/kg of initial xylan in the biomass after only 4 h, equivalent to ~74 to 90 % conversion of XOS into xylobiose. Fermentable glucose yields from enzymatic hydrolysis of solid residues were 8 to 9-fold higher than for untreated material. In view of an integrated biorefinery, we demonstrate the potential for efficient utilisation of Miscanthus for the production of renewable sources, including biochemicals and biofuels.

Extraction and Characterization of Hemicellulose from Eucalyptus By-product: Assessment of Enzymatic Hydrolysis to Produce Xylooligosaccharides

Eucalyptus wood is the primary source of fibers to produce paper and cellulose in South American countries. The major by-product generated in the cellulose industry is sawdust derived from chip wood production, which is designated as Eucalyptus by-product (EB). The xylooligosaccharides (XOS) are xylose-based oligomers with proven effects over maintenance and stimulation of beneficial human gut bacteria. This study reported the EB extraction and characterization along with an assessment of hemicellulose hydrolysis using commercial xylanases to produce XOS. Hemicellulose derived from extracted and NaClO₂ pretreated (HEEBPT) presented xylan content of 55%, which was similar to 58.5% found in commercial Birchwood hemicellulose (CBH). The enzymatic hydrolysis of HEEBPT and CBH presented 30% as maximum conversion of xylan into XOS without significant difference among the enzymatic extracts evaluated. The XOS production from EB was proven as a technically feasible alternative to recover a value-added product from hemicellulosic fraction generated in the cellulose industry. However, lignin removal with NaClO₂ from EB affects the feasibility of an industrial process because they generate toxic compounds in the pretreatment step. Thus, further studies with alternative reagents, such as ionic liquids, are required to asses selectively lignin removal from EB. Graphical Abstract.

Hydrophobic resin treatment of hydrothermal autohydrolysate for prebiotic applications

∼30% of xylooligosaccharides (XOS) in autohydrolysate are likely bonded to lignin “tied,” contributing to loss during resin purification. Loss of “free” XOS depends on DP.

Acetyl-assisted autohydrolysis of sugarcane bagasse for the production of xylo-oligosaccharides without additional chemicals

The aim of this work was to study acetyl-assisted autohydrolysis of sugarcane bagasse for the production of xylo-oligosaccharides without additional chemicals. A xylo-oligosaccharide yield of 50.35% was obtained in 10 min through sugarcane bagasse autohydrolysis at 200 °C; this yield was 49.64% after acetyl-assisted autohydrolysis of a 65:35 mixture of sugarcane bagasse/white birch at 160 °C for 100 min. The yield of xylo-oligosaccharides was close to that obtained at 180 °C/40 min and 200 °C/10 min through the autohydrolysis of sugarcane bagasse. Compared to sugarcane bagasse alone, the xylo-oligosaccharide (degree of polymerization 2-5) yield from the acetyl-assisted autohydrolysis at 200 °C for 10 min was 52.99%. In addition, the yield of glucose from the solid residue following autohydrolysis pretreatment was 96.87% after 72 h of enzymatic hydrolysis. These results demonstrate that acetyl-assisted autohydrolysis is a promising method for the production of xylo-oligosaccharides.

Subcritical Water-Carbon Dioxide Pretreatment of Oil Palm Mesocarp Fiber for Xylooligosaccharide and Glucose Production

The present work aimed to investigate the pretreatment of oil palm mesocarp fiber (OPMF) in subcritical H₂O-CO₂ at a temperature range from 150⁻200 °C and 20⁻180 min with CO₂ pressure from 3⁻5 MPa. The pretreated solids and liquids from this process were separated by filtration and characterized. Xylooligosaccharides (XOs), sugar monomers, acids, furans and phenols in the pretreated liquids were analyzed by using HPLC. XOs with a degree of polymerization X2⁻X4 comprising xylobiose, xylotriose, xylotetraose were analyzed by using HPAEC-PAD. Enzymatic hydrolysis was performed on cellulose-rich pretreated solids to observe xylose and glucose production. An optimal condition for XOs production was achieved at 180 °C, 60 min, 3 MPa and the highest XOs obtained was 81.60 mg/g which corresponded to 36.59% of XOs yield from total xylan of OPMF. The highest xylose and glucose yields obtained from pretreated solids were 29.96% and 84.65%, respectively at cellulase loading of 10 FPU/g-substrate.

Improving Hydrolysis Characteristics of Xylanases by Site-Directed Mutagenesis in Binding-Site Subsites from Streptomyces L10608

The preparation of oligosaccharides via xylan hydrolysis is an effective way to add value to hemicellulosic material of agricultural waste. The bacterial strain Streptomyces L10608, isolated from soil, contains genes encoding xylanases of glucoside hydrolase family 10/11 (GH10/11), and these have been cloned to catalyze the production of xylooligosaccharide (XOS). To improve the XOS proportion of hydrolysates produced by xylanase, four amino acid residues were substituted by site-directed mutagenesis, and the mutant genes were overexpressed in Escherichia coli. Mutations replaced the codons encoding Asn214 (+2) and Asn86 (−2) by Ala and removed the Ricin B-lectin domain in GH10-xyn, and mutants Y115A (−2) and Y123A (−2) were produced for GH11-xyn. Interestingly, GH10-N86Q had significantly increased hydrolysis of XOS and almost eliminated xylose (X1) to <2.5%, indicating that the −2 binding site of GH10-xyn of L10608 is required for binding with xylotriose (X3). The hydrolytic activity of GH10-N86Q was increased approximately 1.25-fold using beechwood xylan as a substrate and had high affinity for the substrate with a low K_m of about 1.85 mg·mL⁻¹. Otherwise, there were no significant differences in enzymatic properties between GH10-N86Q and GH10-xyn. These mutants offer great potential for modification of xylanase with desired XOS hydrolysis.

Sorption of ionizable and ionic organic compounds to biochar, activated carbon and other carbonaceous materials

The sorption of ionic and ionizable organic compounds (IOCs) (e.g., pharmaceuticals and pesticides) on carbonaceous materials plays an important role in governing the fate, transport and bioavailability of IOCs. The paradigms previously established for the sorption of neutral organic compounds do not always apply to IOCs and the importance of accounting for the particular sorption behavior of IOCs is being increasingly recognized. This review presents the current state of knowledge and summarizes the recent advances on the sorption of IOCs to carbonaceous sorbents. A broad range of sorbents were considered to evaluate the possibility to read across between fields of research that are often considered in isolation (e.g., carbon nanotubes, graphene, biochar, and activated carbon). Mechanisms relevant to IOCs sorption on carbonaceous sorbents are discussed and critically evaluated, with special attention being given to emerging sorption mechanisms including low-barrier, charge-assisted hydrogen bonds and cation-π assisted π-π interactions. The key role played by some environmental factors is also discussed, with a particular focus on pH and ionic strength. Overall the review reveals significant advances in our understanding of the interactions between IOCs and carbonaceous sorbents. In addition, knowledge gaps are identified and priorities for future research are suggested.

Evaluation of correlation between glucan conversion and degree of delignification depending on pretreatment strategies using Jabon Merah

The main purpose of this study was to investigate the glucan conversion rate after enzymatic hydrolysis depending on the treatment methods and conditions with changes in the chemical composition of treated solid fraction of Jabon Merah. The glucan conversion rate (17.4%) was not significantly improved after liquid hot water treatment (1st step) even though most of the hemicellulose was dissolved into liquid hydrolysate. Subsequently, dilute acid, organosolv, and peracetic acid treatment (2nd step) was conducted under various conditions to enhance glucan conversion. Among the 2nd step treatment, the glucan conversion rate of organosolv (max. 46.0%) and peracetic acid treatment (max. 65.9%) was increased remarkably through decomposition of acid-insoluble lignin (AIL). Finally, the glucan conversion rate and AIL content were highly correlated, which was revealed by the R-squared value (0.84), but inhibitory factors including cellulose crystallinity must be considered for advanced glucan conversion from highly recalcitrant biomasses, such as Jabon Merah.

Recycling of pre-hydrolysis liquor to improve the concentrations of hemicellulosic saccharides during water pre-hydrolysis of aspen woodchips

In this study, the pre-hydrolysis liquor (PHL) was recycled during aspen chip water pre-hydrolysis, and the effects of PHL recycling on the extraction and accumulation of the hemicellulosic saccharides especially that with high molecular weight in the PHL were studied. The results showed that the concentration of hemicellulose saccharides in PHL depended on the pre-hydrolysis temperature and PHL recycling times. Compared to the unrecycled PHL, the concentration of hemicellulosic saccharides in PHL increased significantly when recycling PHL once or twice at 170°C. Furthermore, the amount of high-molecular-weight hemicelluloses (HMHs) in PHL recycled once at 170°C increased from 2.58g/L (unrecycled) to 6.18g/L, but the corresponding average molecular weight of HMHs decreased from 9.2kDa to 7.6kDa. The concentration of hemicellulosic saccharides in PHL decreased with PHL recycling time at 180°C, accompanied by the formation of a significant amount of furfural.

Development and validation of a HILIC-ELSD method for simultaneous analysis of non-substituted and acetylated xylo-oligosaccharides

A new HILIC-ELSD method was developed for compositional analysis of both xylo-oligosaccharides (XOS) with degree of polymerization (DP) from 2 to 8 and acetylated XOS with DP from 3 to 8. The method was carried out on a zwitterionic HILIC column using ELSD as a detector. The influences of mobile phase composition, column temperature and flow rate on the retention time and resolution of XOS were investigated. An excellent separation result was achieved with a linear gradient elution of 75%-50% acetonitrile in 30min, at a flow rate of 1mL/min and the column temperature at 35°C. In addition, LC-ESI-MS was employed to determine the structural information of X7, X8 and acetylated XOS. The proposed method was simple, reliable, and no derivatization procedure was needed. It is suitable for compositional analysis and quality control of XOS.

Chemical input reduction in the arabinoxylan and lignocellulose alkaline extraction and xylooligosaccharides production

Lignocellulosic material breakdown by hydrolysis is an important step to open new perspectives for bioenergy and special foods production like prebiotic xylooligosaccharides. Improvement of lignocellulose and arabinoxylan alkaline extraction from sugarcane bagasse and enzymatic hydrolysis were performed. Treatments 1 (10% KOH at 70°C), 3 (5% KOH at 121°C) and ZD method (24% KOH at 35°C) showed solid lignocellulose recovery of respectively 75.2%, 74.2% and 73%. A range of 24.8-27% extracted material with high arabinoxylan content (72.1-76.3%) was obtained with these treatments. Treatment 1 and 3 exhibited great KOH reduction in the method reaction, 54.1% and 76.2%, respectively. Likewise, in treatment 3 there was a decrease in ethanol consumption (40.9%) when compared to ZD method. The extracted arabinoxylan showed susceptibility to enzymatic hydrolysis with high solid loading (7%) since Trichoderma reesei xylanases were advantageous for xylose production (54.9%), while Aspergillus fumigatus xylanases achieved better XOS production (27.1%).

Development and validation of a HPLC method for determination of degree of polymerization of xylo-oligosaccharides

A reliable reversed-phase HPLC method was developed for high resolution separation and high sensitivity determination of xylo-oligosaccharides (XOS) with degree of polymerization from 2 to 8. The method was carried out on a Kromasil C18 column using pre-column derivatization with 1-phenyl-3-methyl-5-pyrazolone (PMP) and UV detection at 245nm. The effects of pH value of mobile phase, volume proportion of acetonitrile, concentration of ammonium acetate buffer and flow rate on the retention time and degree of separation of XOS derivatives were investigated. A satisfactory result was achieved in 25min with a mobile phase of 10mmol/L ammonium acetate buffer (pH5.5)-acetonitrile by a gradient elution at 0.8mL/min. In addition, this method was validated by liquid chromatography-tandem mass spectroscopy (LC-MS) analysis and several uncertain compounds were identified. The proposed HPLC method is suitable for the compositional analysis and quality control of XOS.

In Vitro Fermentation of Xylooligosaccharides Produced from Miscanthus × giganteus by Human Fecal Microbiota

Purified xylooligosaccharides from Miscanthus × giganteus (M×G XOS) were used in an in vitro fermentation experiment inoculated with human fecal microbiota. A commercial XOS product and pectin were used as controls. Decreases in pH by 2.3, 2.4, and 2.0 units and production of short-chain fatty acids (SCFA; acetic acid, 7764.2, 6664.1, and 6387.9 μmol/g; propionic acid, 1006.7, 1089.5, and 661.5 μmol/g; and butyric acid, 955.5, 1252.9, and 917.7 μmol/g) were observed in M×G XOS, commercial XOS, and pectin medium after 12 h of fermentation, respectively. Titers of Bifidobacterium spp., Lactobacillus spp., and Escherichia coli increased when fed all three substrates as monitored by qPCR. There was no significant trend for Clostridium perfringens. During fermentation, M×G XOS was statistically equivalent in performance to the commercial XOS sample as measured by culture acidification and growth of health-promoting bacteria and resulted in the highest SCFA production among the three substrates.

Miscanthus×giganteus xylooligosaccharides: Purification and fermentation

A procedure was developed to recover xylooligosaccharides (XOS) from Miscanthus×giganteus (M×G) hydrolyzate. M×G hydrolyzate was prepared using autohydrolysis, and XOS rich fractions were acquired using activated carbon adsorption and stepwise ethanol elution. The combined XOS fractions were purified using a series of ion exchange resin treatments. The end product, M×G XOS, had 89.1% (w/w) total substituted oligosaccharides (TSOS) composed of arabinose, glucose, xylose and acetyl group. Bifidobacterium adolescentis and Bifidobacterium catenulatum (health promoting bacteria) were cultured in vitro on M×G XOS and a commercial XOS source, which was used as a comparison. B. adolescentis grew to a higher cell density than B. catenulatum in both XOS cultures. Total xylose consumption for B. adolescentis was 84.1 and 84.8%, respectively for M×G and commercial XOS cultures; and for B. catenulatum was 76.6 and 73.6%, respectively. The xylobiose (X2), xylotriose (X3) and xylotetraose (X4) were almost utilized for both strains. Acetic and lactic acids were the major fermentation products of the XOS cultures.

Understanding of pH value and its effect on autohydrolysis pretreatment prior to poplar chemi-thermomechanical pulping

Autohydrolysis pretreatment with different severity factors was performed on poplar chips prior to chemi-thermomechanical pulping (CTMP) in order to investigate the change in pH value and its effect on the autohydrolysis pretreatment. The results showed that the dissolution amount of acetic acid increased with raising the severity factor of the pretreatment and declining the size of poplar chips, respectively. Besides, a logarithmic relationship between the amount of acetic acid released in the autohydrolysis liquor (AHL) and pH value of the AHL was observed. The amounts of glucose and xylose (including those in the form of monomers, oligomers, and polysaccharides) as well as furfural and hydroxymethylfurfural (HMF) also depended on the pH value of the AHL to some extent.

Current Pretreatment Technologies for the Development of Cellulosic Ethanol and Biorefineries

Lignocellulosic materials, such as forest, agriculture, and agroindustrial residues, are among the most important resources for biorefineries to provide fuels, chemicals, and materials in such a way to substitute for, at least in part, the role of petrochemistry in modern society. Most of these sustainable biorefinery products can be produced from plant polysaccharides (glucans, hemicelluloses, starch, and pectic materials) and lignin. In this scenario, cellulosic ethanol has been considered for decades as one of the most promising alternatives to mitigate fossil fuel dependence and carbon dioxide accumulation in the atmosphere. However, a pretreatment method is required to overcome the physical and chemical barriers that exist in the lignin-carbohydrate composite and to render most, if not all, of the plant cell wall components easily available for conversion into valuable products, including the fuel ethanol. Hence, pretreatment is a key step for an economically viable biorefinery. Successful pretreatment method must lead to partial or total separation of the lignocellulosic components, increasing the accessibility of holocellulose to enzymatic hydrolysis with the least inhibitory compounds being released for subsequent steps of enzymatic hydrolysis and fermentation. Each pretreatment technology has a different specificity against both carbohydrates and lignin and may or may not be efficient for different types of biomasses. Furthermore, it is also desirable to develop pretreatment methods with chemicals that are greener and effluent streams that have a lower impact on the environment. This paper provides an overview of the most important pretreatment methods available, including those that are based on the use of green solvents (supercritical fluids and ionic liquids).

Screening of Xylanolytic Aspergillus fumigatus for Prebiotic Xylooligosaccharide Production Using Bagasse

Sugarcane bagasse is an important lignocellulosic material studied for the production of xylooligosaccharides (XOS). Some XOS are considered soluble dietary fibre, with low caloric value and prebiotic effect, but they are expensive and not easily available. In a screening of 138 fungi, only nine were shortlisted, and just Aspergillus fumigatus M51 (35.6 U/mL) and A. fumigatus U2370 (28.5 U/mL) were selected as the most significant producers of xylanases. These fungi had low β-xylosidase activity, which is desirable for the production of XOS. The xylanases from Trichoderma reesei CCT 2768, A. fumigatus M51 and A. fumigatus U2370 gave a significantly higher XOS yield, 11.9, 14.7 and 7.9% respectively, in a 3-hour reaction with hemicellulose from sugarcane bagasse. These enzymes are relatively thermostable at 40-50 °C and can be used in a wide range of pH values. Furthermore, these xylanases produced more prebiotic XOS (xylobiose and xylotriose) when compared with a commercial xylanase. The xylanases from A. fumigatus M51 reached a high level of XOS production (37.6%) in 48-72 h using hemicellulose extracted from sugarcane bagasse. This yield represents 68.8 kg of prebiotic XOS per metric tonne of cane bagasse. In addition, in a biorefinery, after hemicellulose extraction for XOS production, the residual cellulose could be used for the production of second-generation ethanol.