Xylooligosaccharides: manufacture and applications

An endoxylanase rapidly hydrolyzes xylan into major product xylobiose via transglycosylation of xylose to xylotriose or xylotetraose

Here, we proposed an effective strategy to enhance a novel endoxylanase (Taxy11) activity and elucidated an efficient catalysis mechanism to produce xylooligosaccharides (XOSs). Codon optimization and recruitment of natural propeptide in Pichia pastoris resulted in achievement of Taxy11 activity to 1405.65 ± 51.24 U/mL. Analysis of action mode reveals that Taxy11 requires at least three xylose (xylotriose) residues for hydrolysis to yield xylobiose. Results of site-directed mutagenesis indicate that residues Glu¹¹⁹, Glu²¹⁰, and Asp⁵³ of Taxy11 are key catalytic sites, while Asp²⁰³ plays an auxiliary role. The novel mechanism whereby Taxy11 catalyzes conversion of xylan or XOSs into major product xylobiose involves transglycosylation of xylose to xylotriose or xylotetraose as substrate, to form xylotetraose or xylopentaose intermediate, respectively. Taxy11 displayed highly hydrolytic activity toward corncob xylan, producing 50.44 % of xylobiose within 0.5 h. This work provides a cost-effective and sustainable way to produce value-added biomolecules XOSs (xylobiose-enriched) from agricultural waste.

Nondigestible Oligosaccharides with Anti-Obesity Effects

Obesity has an important influence on health conditions, causing a multitude of complications and comorbidities, and drug therapy is considered to be one of the treatment strategies. Nowadays, there is increasing interest in the study of intestinal microbiota regulation of obesity; also, an increasing number of agricultural and sideline products have been found to have anti-obesity potential. In the present review, we summarize an overview of current known and potential anti-obesity oligosaccharides and their molecular structures. We describe their anti-obesity potential activity and the molecular structure associated with this activity, the regulation of intestinal microbiota composition and its mechanism of action, including regulation of the short-chain fatty acid (SCFA) pathway and altering bile acid (BA) pathway. This review will provide new ideas for us to develop new anti-obesity functional foods.

Integrated production of prebiotic xylooligosaccharides and high value cellulose from oil palm biomass

Oil palm empty fruit bunch (OPEFB) fibre, which is the byproduct of fruits being stripped from the fresh fruit bunch in palm oil mill, was evaluated in terms of the production of xylooligosaccharides (XOs) and the solid residue was treated for cellulose recovery. Chemoenzymatic hydrolysis that consists of chemical fractionation of OPEFB fibre to isolate xylan with further enzymatic hydrolysis to XOs in a packed bed column reactor (PBCR) was performed. An immobilised xylanase of Thermomyces lanuginosus at the concentration of 8.25 fungal xylanase unit wheat/mililitre (FXUW mL−1) was employed on a PBCR to hydrolyse the xylan at 55 °C and pH 5.5. The yields of XOs are composed of xylopentaose, xylotetraose, xylotriose and xylobiose, successfully produced from the OPEFB-xylan, shown in HPLC analysis with the total production of 8,776 mg/L and the immobilised xylanase can be recycled up to six enzymatic treatment cycles. The solid residue generated from the xylan extraction was further treated with mild concentration of bleaching agents of 20% (v/v) formic acid and 5% (v/v) hydrogen peroxide at 85 °C. The Fourier transform infrared spectroscopy (FTIR) analysis showed that the products obtained have the standard cellulose structure and functional group. Further analyses on the properties of the extracted cellulose in terms of crystallinity, thermal stability and morphology were conducted. The integrated process to produce XOs from OPEFB and recover cellulose from its byproduct is sustainable to extract fine chemicals from OPEFB.

Production, characteristics, and biotechnological applications of microbial xylanases

Microbial xylanases have gathered great attention due to their biotechnological potential at industrial scale for many processes. A variety of lignocellulosic materials, such as sugarcane bagasse, rice straw, rice bran, wheat straw, wheat bran, corn cob, and ragi bran, are used for xylanase production which also solved the great issue of solid waste management. Both solid-state and submerged fermentation have been used for xylanase production controlled by various physical and nutritional parameters. Majority of xylanases have optimum pH in the range of 4.0-9.0 with optimum temperature at 30-60 °C. For biochemical, molecular studies and also for successful application in industries, purification and characterization of xylanase have been carried out using various appropriate techniques. Cloning and genetic engineering are used for commercial-level production of xylanase, to meet specific economic viability and industrial needs. Microbial xylanases are used in various biotechnological applications like biofuel production, pulp and paper industry, baking and brewing industry, food and feed industry, and deinking of waste paper. This review describes production, characteristics, and biotechnological applications of microbial xylanases.

A detailed overview of xylanases: an emerging biomolecule for current and future prospective

Xylan is the second most abundant naturally occurring renewable polysaccharide available on earth. It is a complex heteropolysaccharide consisting of different monosaccharides such as l-arabinose, d-galactose, d-mannoses and organic acids such as acetic acid, ferulic acid, glucuronic acid interwoven together with help of glycosidic and ester bonds. The breakdown of xylan is restricted due to its heterogeneous nature and it can be overcome by xylanases which are capable of cleaving the heterogeneous β-1,4-glycoside linkage. Xylanases are abundantly present in nature (e.g., molluscs, insects and microorganisms) and several microorganisms such as bacteria, fungi, yeast, and algae are used extensively for its production. Microbial xylanases show varying substrate specificities and biochemical properties which makes it suitable for various applications in industrial and biotechnological sectors. The suitability of xylanases for its application in food and feed, paper and pulp, textile, pharmaceuticals, and lignocellulosic biorefinery has led to an increase in demand of xylanases globally. The present review gives an insight of using microbial xylanases as an “Emerging Green Tool” along with its current status and future prospective.

An eco-friendly biorefinery strategy for xylooligosaccharides production from sugarcane bagasse using cellulosic derived gluconic acid as efficient catalyst

A novel approach was proposed for the production of xylooligosaccharides by direct pre-hydrolysis using gluconic acid as catalyst. Maximum xylooligosaccharides (degree of polymerization 2-6) yield of 53.2% could be obtained in 60 min through 5% gluconic acid hydrolysis of sugarcane bagasse at 150 °C. Furthermore, the yield of glucose from solids following gluconic acid hydrolysis treatment was 86.2% after fed-batch enzymatic hydrolysis with 10% solids loading. Results indicated that gluconic acid pretreatment combined with enzymatic hydrolysis could be successfully applied to sugarcane bagasse substrate. Subsequently, glucose could be efficiently bio-oxidized to gluconic acid by Gluconobacter oxydans ATCC 621H with 93.1% yield, and sugarcane bagasse derived gluconic acid has been proved to be an effective catalyst for xylooligosaccharides production. In this study, xylooligosaccharides production from sugarcane bagasse by gluconic acid hydrolysis demonstrated a great potential with respect to the production of these probiotics around the world.

Hemicellulose from Plant Biomass in Medical and Pharmaceutical Application: A Critical Review

BACKGROUND

Due to the non-toxicity, abundance and biodegradability, recently more and more attention has been focused on the exploration of hemicellulose as the potential substrate for the production of liquid fuels and other value-added chemicals and materials in different fields. This review aims to summarize the current knowledge on the promising application of nature hemicellulose and its derivative products including its degradation products, its new derivatives and hemicellulosebased medical biodegradable materials in the medical and pharmaceutical field, especially for inmmune regulation, bacteria inhibition, drug release, anti-caries, scaffold materials and anti-tumor.

METHODS

We searched the related papers about the medical and pharmaceutical application of hemicellulose and its derivative products, and summarized their preparation methods, properties and use effects.

RESULTS

Two hundred and twenty-seven papers were included in this review. Forty-seven papers introduced the extraction and application in immune regulation of nature hemicellulose, such as xylan, mannan, xyloglucan (XG) and β-glucan. Seventy-seven papers mentioned the preparation and application of degradation products of hemicellulose for adjusting intestinal function, maintaining blood glucose levels, enhancing the immunity and alleviating human fatigue fields such as xylooligosaccharides, xylitol, xylose, arabinose, etc. The preparation of hemicellulose derivatives were described in thirty-two papers such as hemicellulose esters, hemicellulose ethers and their effects on anticoagulants, adsorption of creatinine, the addition of immune cells and the inhibition of harmful bacteria. Finally, the preparations of hemicellulose-based materials such as hydrogels and membrane for the field of drug release, cell immobilization, cancer therapy and wound dressings were presented using fifty-five papers.

CONCLUSION

The structure of hemicellulose-based products has the significant impact on properties and the use effect for the immunity, and treating various diseases of human. However, some efforts should be made to explore and improve the properties of hemicellulose-based products and design the new materials to broaden hemicellulose applications.

Biochemical characterization and low-resolution SAXS shape of a novel GH11 exo-1,4-β-xylanase identified in a microbial consortium

Biotechnologies that aim to produce renewable fuels, chemicals, and bioproducts from residual ligno(hemi)cellulosic biomass mostly rely on enzymatic depolymerization of plant cell walls (PCW). This process requires an arsenal of diverse enzymes, including xylanases, which synergistically act on the hemicellulose, reducing the long and complex xylan chains to oligomers and simple sugars. Thus, xylanases play a crucial role in PCW depolymerization. Until recently, the largest xylanase family, glycoside hydrolase family 11 (GH11) has been exclusively represented by endo-catalytic β-1,4- and β-1,3-xylanases. Analysis of a metatranscriptome library from a microbial lignocellulose community resulted in the identification of an unusual exo-acting GH11 β-1,4-xylanase (MetXyn11). Detailed characterization has been performed on recombinant MetXyn11 including determination of its low-resolution small-angle X-ray scattering (SAXS) molecular envelope in solution. Our results reveal that MetXyn11 is a monomeric globular enzyme that liberates xylobiose from heteroxylans as the only product. MetXyn11 has an optimal activity in a pH range from 6 to 9 and an optimal temperature of 50 °C. The enzyme maintained above 65% of its original activity in the pH range 5 to 6 after being incubated for 72 h at 50 °C. Addition of the enzyme to a commercial enzymatic cocktail (CelicCtec3) promoted a significant increase of enzymatic hydrolysis yields of hydrothermally pretreated sugarcane bagasse (16% after 24 h of hydrolysis).

Parageobacillus thermantarcticus, an Antarctic Cell Factory: From Crop Residue Valorization by Green Chemistry to Astrobiology Studies

Knowledge of Antarctic habitat biodiversity, both marine and terrestrial, has increased considerably in recent years, causing considerable development in the studies of life science related to Antarctica. In the Austral summer 1986–1987, a new thermophilic bacterium, Parageobacillus thermantarcticus strain M1 was isolated from geothermal soil of the crater of Mount Melbourne (74°22′ S, 164°40′ E) during the Italian Antarctic Expedition. In addition to the biotechnological potential due to the production of exopolysaccharides and thermostable enzymes, successful studies have demonstrated its use in the green chemistry for the transformation and valorization of residual biomass and its employment as a suitable microbial model for astrobiology studies. The recent acquisition of its genome sequence opens up new opportunities for the use of this versatile bacterium in still unexplored biotechnology sectors.

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.

Low degree of polymerization xylooligosaccharides production from almond shell using immobilized nano-biocatalyst

In this work, the effect of particle size on alkali pretreatment of the almond shell was evaluated for recovery of hemicellulose. Further, endoxylanase from Thermomyces lanuginosus was immobilized on Fe-based magnetic nanoparticles to enable reuse of enzyme. Reduction in particle size significantly influences the recovery of hemicellulose as particle size below 120 μm enable recovery of 97% available hemicellulose in 1 h at 121 °C with 2 M alkali. The enzyme could retain 93.3% of enzymatic activity upon immobilization onto magnetic support using glutaraldehyde (25 mM) and was at par with the free enzyme in terms of pH and temperature profile. The measurement of reaction kinetics (Km and Vmax) indicates similar values for free and immobilized enzyme. The structural and morphological analysis indicates presence near spherical magnetic core and successful cross-linking of the enzyme without alteration of the magnetic core. The immobilized enzyme was able to hydrolyze hemicellulose to produce XOS, the yield equivalent to 67.4% of that obtained using free enzyme at 50 °C. The comparison of XOS production ability at 50 and 60 °C, suggests that the immobilized enzyme retains activity as similar yield was obtained at both temperatures, whereas, the yield for free enzyme decreases significantly. The XOS yield on recycling of immobilized enzyme for three successive cycles was found to reduce to 41% of the initial cycle. However, in all cycles of enzymatic hydrolysis, the percentage of xylobiose was found to be above 90%.

Integrative process for sugarcane bagasse biorefinery to co-produce xylooligosaccharides and gluconic acid

An integrated and green process for co-producing xylooligosaccharides (XOS) and gluconic acid (GA), was developed by utilizing sugarcane bagasse as starting material. In this study, the highest XOS yield of 39.1% obtained from the prehydrolysis was achieved with 10% acetic acid at 150 °C for 45 min. Subsequently, 88.6% conversion of cellulose was achieved in a fed-batch enzymatic hydrolysis using a solid loading of 15%. Results of glucose fermentation suggested that inherent regulatory system of strain Gluconobacter oxydans ATCC 621H boosted GA accumulation without the requirement of pH control, leading to a good 96.3% of GA yield. Great performance of this strain offer an economically feasible option for the large-scale sustainable GA production from biomass. Overall, approximately 105 g XOS and 340 g GA were co-produced from 1 kg of dried sugarcane bagasse as feedstock; this integrated process might be a cost-effective option for the comprehensive utilization of sugarcane bagasse.

Bio-ionic liquid pretreatment and ultrasound-promoted enzymatic hydrolysis of black soybean okara

The effective processing method to produce fermentable sugars and modify the microstructure of black soybean okara using bio-ionic liquid (bio-IL) pretreatment and ultrasound-promoted enzymatic hydrolysis was investigated. The morphology and structural characteristics of okara before and after bio-IL pretreatment and enzymatic hydrolysis under different ultrasonic frequencies were analyzed by field emission scanning electron microscope (FE-SEM), X-ray energy dispersive spectrometer (EDS), and Fourier transform infrared spectroscopy (FTIR). Without pretreatment, the production of total reducing sugar (TRS) under ultrasound (40 kHz/300 W) was 3.4 times of that without ultrasound. Using the bio-IL choline acetate ([Ch][OAc]) in water for the pretreatment of black soybean okara, the TRS production of enzymatic hydrolysis was further increased to 5.2 times of that without ultrasound in 4 h of reaction. The analysis by FTIR and EDS showed that the highly structured matrix of okara was unfolded and broken by the action of combining ultrasound and choline acetate pretreatment, due to which the surface structures with large pores were presented to facilitate the reduction of unfavorable hindrance for enzymatic hydrolysis. The simplified kinetic model was proposed to describe the transport and reaction phenomena of enzymes in a solid-liquid system by using two kinetic parameters to show the impeded behavior of enzyme within the matrix of okara. The combination of bio-IL pretreatment and ultrasound-promoted enzymatic hydrolysis was able to make the efficient structural changes of black soybean okara to enhance the digestion of enzymes, and the okara could be valorized for use in foods.

Lignocellulose derived functional oligosaccharides: production, properties, and health benefits

Lignocellulosic biomass (LB) is the renewable feedstock for the production of fuel/energy, feed/food, chemicals, and materials. LB could also be the versatile source of the functional oligosaccharides, which are non-digestible food ingredients having numerous applications in food, cosmetics, pharmaceutical industries, and others. The burgeoning functional food demand is expected to be more than US$440 billion in 2022. Because of higher stability at low pH and high temperature, oligosaccharides stimulate the growth of prebiotic bifidobacteria and lactic acid bacteria. Xylooligosaccharides (XOS) are major constituents of oligosaccharides consisting of 2-7 xylose monomeric units linked via β-(1,4)-linkages. XOS can be obtained from various agro-residues by thermochemical pretreatment, enzymatic or chemoenzymatic methods. While thermochemical methods are fast, reproducible, enzymatic methods are substrate specific, costly, and produce minimum side products. Enzymatic methods are preferred for the production of food grade and pharmaceutically important oligosaccharides. XOS are potent prebiotics having antioxidant properties and enhance the bio-adsorption of calcium and improving bowel functions, etc. LB can cater to the increasing demand of oligosaccharides because of their foreseeable amount and the advancements in technology to recover oligosaccharides. This paper summarizes the methods for oligosaccharides production from LB, classification, and benefits of oligosaccharides on human health.

Rapid Nondestructive Fractionation of Biomass (≤15 min) by using Flow-Through Recyclable Formic Acid toward Whole Valorization of Carbohydrate and Lignin

Whole valorization of carbohydrate and lignin from biomass was achieved by rapid flow-through fractionation (RFF) within 15 min. Wheat straw was effectively deconstructed into its principle components without degradation by using easily recyclable aqueous formic acid (72 wt %) at 130 °C. The obtained cellulose-rich solid showed a nearly complete glucan recovery and 73.8 % glucose conversion after enzymatic hydrolysis. Xylan also reached full recovery with negligible furfural formation with a sum of 80 % of oligo/mono xylose in spent liquor and 20 % of xylan remaining in the solid. Up to 75.4 % lignin was dissolved in the spent liquor and further fractionated into water-insoluble (WIL) and water-soluble lignin (WSL) by dilution with water. WIL showed a non-condensed and well-preserved structure with 84.5 % β-O-4 remaining, which is believed to be beneficial for catalytic conversion into low-molecular-weight chemicals and fuels. The concentration of employed formic acid was below the formic acid/water azeotrope, and therefore the reaction medium could be restored through simple distillation. Together with the joint valorization of lignin and carbohydrates, the presented RFF is a promising process for sustainable biorefinery.

Enzymatic hydrolysis of tropical weed xylans using xylanase from Aureobasidium melanogenum PBUAP46 for xylooligosaccharide production

The maximum yield of xylanase from Aureobasidium melanogenum PBUAP46 was 5.19 ± 0.08 U ml^-1 when cultured in a production medium containing 3.89% (w/v) rice straw and 0.75% (w/v) NaNO₃ as carbon and nitrogen sources, respectively, for 72 h. This enzyme catalyzed well and was relatively stable at pH 7.0 and room temperature (28 ± 2 °C). The produced xylanase was used to hydrolyze xylans from four tropical weeds, whereupon it was found that the highest amounts of reducing sugars in the xylan hydrolysates of cogon grass (Imperata cylindrical), Napier grass (Pennisetum purpureum), and vetiver grass (Vetiveria zizanioides) were at 20.44 ± 0.84, 17.50 ± 0.29, and 19.44 ± 0.40 mg 100 mg xylan^-1, respectively, but it was not detectable in water hyacinth (Eichhornia crassipes) hydrolysate. The highest combined amount of xylobiose and xylotriose was obtained from vetiver grass; thus, it was selected for further optimization. After optimization, xylanase digestion of vetiver grass xylan at 27.94 U g xylan^-1 for 92 h 19 min gave the highest amount of reducing sugars (23.65 ± 1.34 mg 100 mg xylan^-1), which were principally xylobiose and xylotriose. The enriched XOs exhibited a prebiotic property, significantly stimulating the growth of Lactobacillus brevis and L. casei by a factor of up to 3.5- and 6.5-fold, respectively, compared to glucose.

Enzymatic production of xylooligosaccharides from Brazilian Syrah grape pomace flour: a green alternative to conventional methods for adding value to agricultural by- products

BACKGROUND

The aim of this work was to determine the most favorable conditions for the production of xylooligosaccharides (XOS) from Brazilian Syrah grape pomace. Chemical processes were performed using a rotatable central composite design where the concentration of sulfuric acid or sodium hydroxide and the grape pomace flour/solvent mass ratio were the dependent variables. Enzymatic production was also evaluated using xylanase produced by Aspergillus niger 3T5B8 and Viscozyme^® enzymatic commercial cocktail.

RESULTS

Chemical extraction allowed to recover 21.8-74.6% and 5.2-96.3% of total XOS for acidic and alkaline processes respectively. Enzymatic production extracted up to 88.68 ± 0.12% of total XOS using xylanase and up to 84.09 ± 2.40% with Viscozyme^® .

CONCLUSION

The present study demonstrated different feasible methods to produce high-added-value molecules, i.e. XOS, from Syrah grape pomace flour, valorizing this major by-product. The use of enzymatic cocktails demonstrated to be an alternative to the conventional methods, allowing to obtain an eco-friendly and sustainable grape pomace extract. © 2018 Society of Chemical Industry.

Synergistic effect of acetyl xylan esterase from Talaromyces leycettanus JCM12802 and xylanase from Neocallimastix patriciarum achieved by introducing carbohydrate-binding module-1

Wheat bran is an effective raw material for preparation xylooligosaccharides; however, current research mainly focuses on alkali extraction and enzymatic hydrolysis methods. Since ester bonds are destroyed during the alkali extraction process, xylanase and arabinofuranosidase are mainly used to hydrolyze xylooligosaccharides. However, alkali extraction costs are very high, and the method also causes pollution. Therefore, this study focuses on elucidating a method to efficiently and directly degrade destarched wheat bran. First, an acidic acetyl xylan esterase (AXE) containing a carbohydrate-binding module-1 (CBM1) domain was cloned from Talaromyces leycettanus JCM12802 and successfully expressed in Pichia pastoris. Characterization showed that the full-length acetyl xylan esterase AXE + CBM1 was similar toe uncovered AXE with an optimum temperature and pH of 55 °C and 6.5, respectively. Testing the acetyl xylan esterase and xylanase derived from Neocallimastix patriciarum in a starch-free wheat bran cooperative experiment revealed that AXE + CBM1 and AXE produced 29% and 16% reducing sugars respectively, compared to when only NPXYN11 was used. In addition, introduced the CBM1 domain into NPXYN11, and the results indicated that the CBM1 domain showed little effect on NPXYN11 properties. Finally, the systematically synergistic effects between acetyl xylan esterase and xylanase with/without the CBM1 domain demonstrated that the combined ratio of AXE + CBM1 coming in first and NPXYN11 + CBM1 s increased reducing sugars by almost 35% with AXE and NPXYN11. Furthermore, each component's proportion remained the same with respect to xylooligosaccharides, with the largest proportion (86%) containing of 49% xylobiose and 37% xylotriose.

GH-10 and GH-11 Endo-1,4-β-xylanase enzymes from Kitasatospora sp. produce xylose and xylooligosaccharides from sugarcane bagasse with no xylose inhibition

A novel strategy for the low-cost, high-yield co-production of xylose and xylooligosaccharides together with no xylose inhibition was developed using a novel heterologous expression of XYN10Ks_480 endo-1,4-β-xylanase with a ricin-type β-trefoil type of domain and XYN11Ks_480 endo-1,4-β-xylanase with a CBM 2 superfamily from the Kitasatospora sp in an actinomycetes expression system. Xylose is the main building block for hemicellulose xylan. Our findings demonstrated high levels of expression and catalytic activity for XYN10Ks_480 during hydrolysis of the extracted xylan of bagasse, and three types of xylan-based substrates were used to produce xylose and xylooligosaccharides. However, hydrolysis by XYN11Ks_480 produced xylooligosaccharides without xylose formation. This study demonstrated how integrating sodium hypochlorite-extracted xylan and enzymatic hydrolysis could provide an alternative strategy for the generation of XOS from lignocellulosic material.

Eco-friendly consolidated process for co-production of xylooligosaccharides and fermentable sugars using self-providing xylonic acid as key pretreatment catalyst

BACKGROUND

Obtaining high-value products from lignocellulosic biomass is central for the realization of industrial biorefinery. Acid pretreatment has been reported to yield xylooligosaccharides (XOS) and improve enzymatic hydrolysis. Moreover, xylose, an inevitable byproduct, can be upgraded to xylonic acid (XA). The aim of this study was to valorize sugarcane bagasse (SB) by starting with XA pretreatment for XOS and glucose production within a multi-product biorefinery framework.

RESULTS

SB was primarily subjected to XA pretreatment to maximize the XOS yield by the response surface method (RSM). A maximum XOS yield of 44.5% was achieved by acid pretreatment using 0.64 M XA for 42 min at 154 °C. Furthermore, XA pretreatment can efficiently improve enzymatic digestibility, and achieved a 90.8% cellulose conversion. In addition, xylose, the inevitable byproduct of the acid-hydrolysis of xylan, can be completely converted to XA via bio-oxidation of Gluconobacter oxydans (G. oxydans). Subsequently, XA and XOS can be simultaneously separated by electrodialysis.

CONCLUSIONS

XA pretreatment was explored and exhibited a promising ability to depolymerize xylan into XOS. Mass balance analysis showed that the maximum XOS and fermentable sugars yields reached 10.5 g and 30.9 g per 100 g raw SB, respectively. In summary, by concurrently producing XOS and fermentable sugars with high yields, SB was thus valorized as a promising feedstock of lignocellulosic biorefinery for value-added products.

Nondigestible carbohydrates, butyrate, and butyrate-producing bacteria

Nondigestible carbohydrates (NDCs) are fermentation substrates in the colon after escaping digestion in the upper gastrointestinal tract. Among NDCs, resistant starch is not hydrolyzed by pancreatic amylases but can be degraded by enzymes produced by large intestinal bacteria, including clostridia, bacteroides, and bifidobacteria. Nonstarch polysaccharides, such as pectin, guar gum, alginate, arabinoxylan, and inulin fructans, and nondigestible oligosaccharides and their derivatives, can also be fermented by beneficial bacteria in the large intestine. Butyrate is one of the most important metabolites produced through gastrointestinal microbial fermentation and functions as a major energy source for colonocytes by directly affecting the growth and differentiation of colonocytes. Moreover, butyrate has various physiological effects, including enhancement of intestinal barrier function and mucosal immunity. In this review, several representative NDCs are introduced, and their chemical components, structures, and physiological functions, including promotion of the proliferation of butyrate-producing bacteria and enhancement of butyrate production, are discussed. We also describe the strategies for achieving directional accumulation of colonic butyrate based on endogenous generation mechanisms.

Prebiotic compounds from agro-industrial by-products

Prebiotics are nondigestible food components that have an impact on gut microbiota composition and activity, which in turn results in the improvement of health conditions. Nowadays, the production of prebiotics from agro-industrial by-products is under investigation. In this regard, polysaccharides are usually found in these sources and their potential use as prebiotics has been studied recently since these compounds act as substrates for the human gut microbiota, and they have the potential to modulate its composition through many mechanisms. Additionally, the use of agricultural by-products is advantageous because it is a cheap and abundantly available material. This review focuses on the recent scientific literature regarding the prebiotic properties of polysaccharides from agro-industrial by-products. PRACTICAL APPLICATIONS: Currently, the maintenance of gut homeostasis is a target for the improvement of human health. This review can broaden the perspective on the utilization of agro-industrial by-products that can compete in the market with the commercial ones or act as a source for new food ingredients.

Potential of Fructooligosaccharides and Xylooligosaccharides as Substrates To Counteract the Undesirable Effects of Several Antibiotics on Elder Fecal Microbiota: A First in Vitro Approach

Fructooligosaccharides (FOS) and xylooligosaccharides (XOS) were employed as substrates for in vitro fermentations to assess their capacity to counteract the effects caused by three antibiotics (ABs) at different doses on the elderly gut microbiota and its metabolic activity. The AB type and dose scarcely affected the total bacterial numbers and the microbiota composition after 24 h. However, in the presence of ABs, the relative percentages of Lactobacillus decreased (from 11.4% to 3.2% in the presence of XOS1), as well as the butyrate production, whereas the population of Bacteroides increased significantly in the presence of XOS1 (from 27.5% to 55.7%). FOS were able to counteract these effects by increasing the butyrate production and the number of Lactobacillus, while maintaining the number of Bacteroides almost constant and decreasing the clostridia. XOS2 (mainly DP = 2-4) also showed ability to increase the percentages of Bifidobacterium and the production of both butyrate and acetate.

Effect of disulfide bridge on hydrolytic characteristics of xylanase from Penicillium janthinellum

Highly efficient and stable enzymes are required for application in biotechnology, to meet the technical, environmental, and economic industrial demands. Xylanases are hemicellulolytic enzymes that degrade the heteroxylan constituent of the lignocellulosic plant cell wall. In this study, an acidic xylanase designated Pjxyn (pH 4.0) from Penicillium janthinellum was engineered by the introduction of a disulfide bridge. This strategy exploited the influence of the bridge on hydrolysis characteristics and enhanced hydrolysis was achieved. Three mutants [PjxynS(27)S(39), PjxynS(27)S(186), and PjxynS(39)S(186)] produced more xylose and xylobiose as hydrolysis products compared with the wild-type Pjxyn, when commercial xylans and lab-prepared water-insoluble corncob-xylan were used as the substrates, especial for the PjxynS(27)S(39) mutant, the content of xylose and xylobiose was 87.62% (using beechwood xylan) and 69.91% (using oat-spelt xylan) higher than that in the hydrolysis products of Pjxyn. Moreover, each mutant combined with the xylanase mutant T-XynFM effectively decreased the production of xylose with an optimum xylobiose yield. The findings demonstrate the potential industrial value of engineering xylanase to improve its hydrolytic properties and thermostability.

Structural characterization of hemicellulose released from corn cob in continuous flow type hydrothermal reactor

Hydrothermal reaction is known to be one of the most efficient procedures to extract hemicelluloses from lignocellulosic biomass. We investigated the molecular structure of xylooligosaccharides released from corn cob in a continuous flow type hydrothermal reactor designed in our group. The fraction precipitable from the extract with four volumes of ethanol was examined by ¹H-NMR spectroscopy and MALDI-TOF MS before and after enzymatic treatment with different purified enzymes. The released water-soluble hemicellulose was found to correspond to a mixture of wide degree of polymerization range of acetylarabinoglucuronoxylan fragments (further as corn cob xylan abbreviated CX). Analysis of enzymatic hydrolyzates of CX with an acetylxylan esterase, GH3 β-xylosidase, GH10 and GH11 xylanases revealed that the main chain contains unsubstituted regions mixed with regions of xylopyranosyl residues partially acetylated and occasionally substituted by 4-O-methyl-d-glucuronic acid and arabinofuranose esterified with ferulic or coumaric acid. Single 2- and 3-O-acetylation was accompanied by 2,3-di-O-acetylation and 3-O-acetylation of Xylp residues substituted with MeGlcA. Most of the non-esterified arabinofuranose side residues were lost during the hydrodynamic process. Despite reduced branching, the acetylation and ferulic acid modification of pentose residues contribute to high yields and high solubility of the extracted CX. It is also shown that different enzyme treatments of CX may lead to various types of xylooligosaccharides of different biomedical potential.

Identification and characterization of a novel KG42 xylanase (GH10 family) isolated from the black goat rumen-derived metagenomic library

This study was conducted to isolate and functionally characterize a novel xylan-degrading enzyme from the microbial metagenomes of black goat rumens. A novel gene, KG42, was isolated from one of the 17 xylan-degrading metagenomic fosmid clones obtained from black goat rumens. The KG42 gene, comprising a 1107 bp open reading frame, encodes a protein composed of 368 amino acids (41 kDa) with a glycosyl hydrolase family 10 (GH10) domain, consisting of a "salad-bowl" shaped tertiary structure (a typical 8-fold α/β barrel (α/β)8) and two catalytic residues. KG42 xylanase protein has at best 40% sequence identity with other homologous GH10 xylanase proteins. The enzyme displayed its optimum activity at pH 5.0 and 50 °C. The enzyme was thermally stable at pH and temperature ranges of 5.0-10.0 and 20-60 °C, respectively. Substrate specificity and hydrolytic patterns implied that the KG42 xylanase functions as an endo-β-1,4-xylanase (EC 3.2.1.8). The KG42 xylanase was also used for the preparation of bifidogenic xylan hydrolysates, demonstrating its potential applications toward preparing prebiotic xylooligosaccharides.

Optimization of alkaline pretreatment and enzymatic hydrolysis for the extraction of xylooligosaccharide from rice husk

Rice husk (RH) is the major agricultural waste obtained during rice hulling process, which can be a sustainable source of xylooligosaccharide (XOS). The current study deals with the production of XOS from Thai rice husk using alkaline pretreatment and enzyme hydrolysis method. The response surface methodology consisted of central composite design and Box–Behnken design was employed to achieve the maximum response in alkaline pretreatment and XOS production, respectively. The optimum conditions for alkaline pretreatment to recover maximum xylan yield were 12–18% of alkaline concentration, the temperature at 110–120 °C, and steaming time for 37.5–40 min. The FTIR results suggested that the extracted sample was the xylan fraction. The maximum XOS production of 17.35 ± 0.31 mg XOS per mL xylan was observed in the run conditions of 6.25 mg enzyme per g xylan, 9 h of incubation time, and 5% of xylan. The results revealed that the xylan extracted from RH by using an effective base couple with the steam application and the enzymatic hydrolysis help to maximize the yield of XOS, which can be further used in functional foods and dietary supplements.

High xylan recovery using two stage alkali pre-treatment process from high lignin biomass and its valorisation to xylooligosaccharides of low degree of polymerisation

In the present work, xylan from arecanut husk was extracted using 2 stage alkaline pretreatment process. In first step, biomass was incubated in alkali at different temperatures (25 °C, 50 °C and 65 °C), alkali concentrations (5%, 10%, 15% and 20% w/v), and incubation periods (8 h, 16 h and 24 h) and evaluated for xylan recovery. It was observed that 40-52% of available xylan could be recovered using 10% alkali when incubated for 8-24 h at 65 °C. Subsequently, the alkali pretreatment operating conditions which provided good xylan recovery were processed further using hydrothermal treatment to extract more xylan. For maximum xylan recovery (>90%), best operating conditions were identified when biomass was treated under hydrothermal treatment (1, 1.5 and 2 h) with varying incubation periods (8, 16, 24 h) and alkali concentrations (5%, 10%) using full factorial design. Incubating arecanut husk with 10% w/v NaOH, at 65 °C for a period of 8 h, followed by hydrothermal treatment at 121 °C for 1 h helped recover >94% xylan. In the next step, enzymatic hydrolysis process was optimized to recover maximum XOS (Optimized condition: 50 °C, pH 4 and 10 U enzyme dose). The hydrolysate comprised of xylobiose: 25.0 ± 1.2 g/100 g xylan (∼71% of XOS), xylotriose: 9.2 ± 0.65 g/100 g xylan (26.2% of XOS) and xylotetrose: 0.9 ± 0.04 g/100 g xylan (2% of XOS). The developed process enables to reduce alkali consumption for high recovery of xylan from biomass with relatively higher lignin content for its valorisation into a potential prebiotic oligosaccharide.