Enzymatic production of Xylooligosaccharide from selected agricultural wastes

Enzymatic production of xylooligosaccharide from lignocellulosic and marine biomass: A review of current progress, challenges, and its applications in food sectors

Over the last decade, xylooligosaccharides (XOS) have attracted great attentions because of their unique chemical properties and excellent prebiotic effects. Among the current strategies for XOS production, enzymatic hydrolysis is preferred due to its green and safe process, simplicity in equipment, and high control of the degrees of polymerization. This paper comprehensively summarizes various lignocellulosic biomass and marine biomass employed in enzymatic production of XOS. The importance and advantages of enzyme immobilization in XOS production are also discussed. Many novel immobilization techniques for xylanase are presented. In addition, bioinformatics techniques for the mining and designing of new xylanase are also described. Moreover, XOS has exhibited great potential applications in the food industry as diverse roles, such as a sugar replacer, a fat replacer, and cryoprotectant. This review systematically summarizes the current research progress on the applications of XOS in food sectors, including beverages, bakery products, dairy products, meat products, aquatic products, food packaging film, wall materials, and others. It is anticipated that this paper will act as a reference for the further development and application of XOS in food sectors and other fields.

Xylooligosaccharides from lignocellulosic biomass and their applications as nutraceuticals: a review on their production, purification, and characterization

Xylooligosaccharides (XOS) are considered a potent source of prebiotics for humans. The global prebiotic market is expanding in size, was valued at USD 6.05 billion in 2021, and is expected to grow at a 14.9% compound annual growth rate between 2022 and 2030, indicating a huge demand. These XOS are non-digestible pentose sugar oligomers comprising mainly xylose. Xylose is naturally present in the lignocellulosic biomass (LCB), fruits and vegetables. Apart from the prebiotic effect, these XOS have been reported to reduce blood cholesterol, possess antioxidant effects, increase calcium absorption, reduce colon cancer risk, and benefit diabetic patients. The primary use of XOS is reported in the feed industry followed by health, medical use, food and drinks. LCB mainly contains glucan, xylan and lignin. After glucan, xylan is the second-highest available sugar on the globe composed of xylose. Therefore, the xylan fraction of LCB has great significance in producing food, feed and energy. Glucan has been exploited for the commercial production of ethanol, xylitol, furfural, hydroxymethyl furfural and glucose. As of now, xylan has limited applications. Therefore, xylan can be exploited to convert to XOS. The production of XOS from LCB fraction not only helps to produce these at a very low price, but also helps in the reduction of greenhouse gases. Its use in food and drinks is increasing as it can be derived from the abundantly and cheaply available LCB. The article provides a review on the production, purification and characterization of XOS in view of their use as nutraceuticals. © 2024 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Impact of adding xylooligosaccharides encapsulated in butter: Microstructural, optical, rheological and sensory aspects

This study investigated the microstructure, rheological properties, and sensory characteristics of butters produced with free and encapsulated xylooligosaccharides (XOS). Four formulations of butter were processed: BCONT: 0 % w/w XOS (control); BXOS: 20% w/w free XOS; BXOS-ALG: 20% w/w XOS microencapsulated with alginate (XOS-alginate ratio of 3:1 w/w); and BXOS-GEL: 20% w/w XOS microencapsulated with alginate-gelatin (XOS-alginate-gelatin ratio of 3:1:1.5 w/w). The microparticles showed a bimodal distribution, low size and low span values, demonstrating physical stability to be included in emulsions. The XOS-ALG presented surface weighted mean diameter (D3.2) of 90.24 µm, volume-weighted mean diameter (D4.3) of 131.8 µm, and Span of 2.14. In contrast, the XOS-GEL presented D3.2 of 82.80 µm, D4.3 of 141.0 µm, and a Span of 2.46. Products with XOS were characterized by higher creaminess, sweet taste, and lower salty taste than the control. However, the addition form significantly impacted the other evaluated parameters. The utilization of XOS in a free form (BXOS) resulted in smaller droplet sizes (1.26 μm) than encapsulated XOS and control (XOS-ALG = 1.32 µm / XOS-GEL = 1.58 µm, / BCONT = 1.59 µm), and changes in the rheological parameters (higher values of shear stress, viscosity, consistency index, rigidity (J0), and Newtonian viscosity (ηN) and lower elasticity (τ)). Furthermore, it changed the color parameters (more yellow and dark color, lower L* and higher b* values). On the other hand, the utilization of micropaticles of XOS (BXOS-ALG and BXOS-GEL) kept shear stress, viscosity, consistency index, rigidity (J0), and elasticity (τ) more similar to control. The products had a less intense yellow color (lower b* values) and was perceived with more consistency and butter taste. However, the presence of particles was perceived by consumers. The results suggest that consumers were more attentive to reporting flavor-related attributes than texture. In conclusion, adding microparticles of XOS could improve butter's rheological and sensory properties. In conclusion, adding microparticles of XOS could improve butter's rheological and sensory properties.

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.

Extraction, Isolation, and Purification of Value-Added Chemicals from Lignocellulosic Biomass

This review covers the operating conditions for extracting top value-added chemicals, such as levulinic acid, lactic acid, succinic acid, vanillic acid, 3-hydroxypropionic acid, xylitol, 2,5-furandicarboxylic acid, 5-hydroxymethyl furfural, chitosan, 2,3-butanediol, and xylo-oligosaccharides, from common lignocellulosic biomass. Operating principles of novel extraction methods, beyond pretreatments, such as Soxhlet extraction, ultrasound-assisted extraction, and enzymatic extraction, are also presented and reviewed. Post extraction, high-value biochemicals need to be isolated, which is achieved through a combination of one or more isolation and purification steps. The operating principles, as well as a review of isolation methods, such as membrane filtration and liquid–liquid extraction and purification using preparative chromatography, are also discussed.

Identification and Characterization of a Novel Endo-β-1,4-Xylanase from Streptomyces sp. T7 and Its Application in Xylo-Oligosaccharide Production

A xylanase-producing strain, identified as Streptomyces sp. T7, was isolated from soil by our lab. The endo-β-1,4-xylanase (xynST7) gene was found in the genome sequence of strain T7, which was cloned and expressed in Escherichia coli. XynST7 belonged to the glycoside hydrolase family 10, with a molecular mass of approximately 47 kDa. The optimum pH and temperature of XynST7 were pH 6.0 and 60 °C, respectively, and it showed wide pH and temperature adaptability and stability, retaining more than half of its enzyme activity between pH 5.0 and 11.0 below 80 °C. XynST7 showed only endo-β-1,4-xylanase activity without cellulase- or β-xylosidase activity, and it showed maximal hydrolysis for corncob xylan in all the test substrates. Then, XynST7 was used for the production of xylo-oligosaccharides (XOSs) by hydrolyzing xylan extracted from raw corncobs. The maximum yield of the XOS was 8.61 ± 0.13 mg/mL using 15 U/mL of XynST7 and 1.5% corncob xylan after 10 h of incubation at 60 °C. The resulting hydrolysate products mainly consisted of xylobiose and xylotriose. These data indicated that XynST7 might by a promising tool for various industrial applications.

Chemical and Enzymatic Synthesis of Biobased Xylo-Oligosaccharides and Fermentable Sugars from Wheat Straw for Food Applications

Xylo-oligosaccharides are sugar oligomers with 2~7 xylose units considered non-digestible fibers that can be produced from biodegradable and low-cost biomass like wheat straw. An integrated approach consisting of hydrothermal pretreatment, alkaline treatment, enzymatic treatment and the combinations thereof was applied to overcome the recalcitrance structure of the wheat straw and allow selective fractioning into fermentable sugars and xylo-oligosaccharides. The hydrolysates and processed solids were chemically characterized by High-performance liquid chromatography and Ion chromatography, and the results were expressed as function of the severity factor and statistically interpreted. The concentration of fermentable sugars (glucose, xylose, arabinose) was the highest after the combination of alkaline and enzymatic treatment with xylanase (18 g/L sugars), while xylo-oligosaccharides (xylotriose and xylotetraose) were released in lower amounts (1.33 g/L) after the same treatment. Refining experiments were carried out to obtain a purified fraction by using anion and cation exchange chromatography. The polymer adsorber resin MN-502 showed efficient removal of salts, phenols and furan derivatives. However, the xylo-oligosaccharides yields were also slightly reduced. Although still requiring further optimization of the treatments to obtain higher purified oligomer yields, the results provide information on the production of xylo-oligosaccharides and fermentable sugars from wheat straw for potential use in food applications.

Microwave-assisted enzymatic hydrolysis to produce xylooligosaccharides from rice husk alkali-soluble arabinoxylan

The prebiotic properties of xylooligosaccharides (XOS) and arabino-xylooligosaccharides (AXOS) produced from rice husk (RH) using microwave treatment combined with enzymatic hydrolysis were evaluated. The RH was subjected to microwave pretreatment at 140, 160 and 180 °C for 5, 10 and 15 min to obtain crude arabinoxylan (AX). Increasing microwave pretreatment time increased sugar content. Crude AX was extracted with 2% (w/v) sodium hydroxide at 25 °C for 24 h and used as a substrate for XOS production by commercial xylanases. Results showed that oligosaccharides produced by Pentopan Mono BG and Ultraflo Max provided xylobiose and xylotriose as the main products. AXOS was also present in the oligosaccharides that promoted growth of Lactobacillus spp. and resisted degradation by over 70% after exposure to simulated human digestion.

Ozone assisted autohydrolysis of wheat bran enhances xylooligosaccharide production with low generation of inhibitor compounds: A comparative study

In the present study, ozone assisted autohydrolysis (OAAH) was evaluated for enhanced generation of xylooligosaccharide (XOS) from wheat bran. The total XOS yield with optimum ozone dose of 3% (OAAH-3) was found to be 8.9% (w/w biomass) at 110 °C in comparison to 7.96% at 170 °C by autohydrolysis (AH) alone. Although, there was no significant difference in oligomeric composition (DP 2-6), significant decrease in degradation products namely furfural (2.78-fold), HMF (3.15-fold), acrylamide (nil) and acetic acid (1.06-fold), was observed with OAAH-3 as a pretreatment option. There was 1-fold higher xylan to XOS conversion and OAAH-hydrolysate had higher DPPH radical scavenging activity than AH. PCA plots indicated clear enhancement in XOS production and lower generation of inhibitors with decrease in treatment temperature. Results of the study therefore suggest OAAH can be an effective pretreatment option that can further be integrated with downstream processing for concentration and purification of XOS.

Evaluating the addition of xylooligosaccharides into alginate-gelatin hydrogels

Xylooligosaccharides (XOS) are emerging prebiotic that may improve structural features of biopolymer blends. The investigation around the conformation of XOS into the matrix of alginate and gelatin clarifies the potential applications of this formulation in the food industry as texture modifiers or encapsulation systems. Structural properties verified by flow behavior, SEM, XRD, and FT-IR demonstrated that the add up to 3% XOS into the alginate-gelatin blend formed a cohesive matrix, with smaller pores and crystalline structure, confirming the potential of xylooligosaccharides hydrogels for the development of functional and synbiotic foods.

Paecilomyces variotii xylanase production, purification and characterization with antioxidant xylo-oligosaccharides production

Paecilomyces variotii xylanase was, produced in stirred tank bioreactor with yield of 760 U/mL and purified using 70% ammonium sulfate precipitation and ultra-filtration causing 3.29-fold purification with 34.47% activity recovery. The enzyme purity was analyzed on sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) confirming its monomeric nature as single band at 32 KDa. Zymography showed xylan hydrolysis activity at the same band. The purified enzyme had optimum activity at 60 °C and pH 5.0. The pH stability range was 5-9 and the temperature stability was up 70 °C. Fe²⁺and Fe³⁺ exhibited inhibition of xylanase enzyme while Cu²⁺, Ca²⁺, Mg²⁺ and Mn²⁺ stimulated its activity. Mercaptoethanol stimulated its activity; however, Na₂-EDTA and SDS inhibited its activity. The purified xylanase could hydrolyze beechwood xylan but not carboxymethyl cellulose (CMC), avicel or soluble starch. Paecilomyces variotii xylanase K_m and V_max for beechwood were determined to be 3.33 mg/mL and 5555 U/mg, respectively. The produced xylanase enzyme applied on beech xylan resulted in different types of XOS. The antioxidant activity of xylo-oligosaccharides increased from 15.22 to 70.57% when the extract concentration was increased from 0.1 to 1.5 mg/mL. The enzyme characteristics and kinetic parameters indicated its high efficiency in the hydrolysis of xylan and its potential effectiveness in lignocellulosic hydrolysis and other industrial application. It also suggests the potential of xylanase enzyme for production of XOS from biomass which are useful in food and pharmaceutical industries.

Xylo-oligosaccharide microparticles with synbiotic potential obtained from enzymatic hydrolysis of sugarcane straw

Synbiotic formulations and microencapsulation techniques have been explored in food industries to guarantee the viability of probiotic organisms; playing an important role in microbiota balance. Microparticles of alginate, gelatin and xylo-oligosaccharides (XOS) were produced by external gelation with the purpose of enhancing the survival rate of the probiotic L. acidophilus. XOS was obtained through enzymatic hydrolysis of xylan extracted from sugarcane straw, achieving more than 70% conversion and used for microparticle preparation. Microparticles containing 3% XOS provided greater cell protection during exposure to the gastrointestinal tract and during refrigerated storage; keeping 97.86 ± 0.44% of viability during 28 days of storage and enabling 87.50 ± 0.02% survival after digestive simulation. However, particles without XOS showed 84.49 ± 0.59% of viability after storage and 68.45 ± 0.03% after digestion assay. These results lead to promising applications in synbiotic and functional food formulations comprised of components requiring extended shelf-life, protection from gastrointestinal conditions and gradual bioactive delivery.

Enzymatic production of xylooligosaccharide from date (Phoenix dactylifera L.) seed

Date palm (phonix dactylifera L.) is an important tropical fruit growing in central and southern regions of Iran. Date seed is composed of cellulose, hemicellulose, and lignin, that make it an excellent candidate for xylooligosaccharide (XOS) production. In this study, two different protocols are used for the extraction of hemicellulose from date seeds. In the first protocol, hemicellulose (xylan1) was extracted by 2.25 M alkaline solution at room temperature for 24 hr. In the second protocol, date seed was treated with LCHTA (low concentration, 0.1 M, high temperature, 80°C, alkaline solution) for 3 hr, and thereafter, hemicellulose (xylan2) was extracted by 2.25 M alkaline solution at room temperature for 24 hr. The carbohydrate units of xylan1 and xylan2 were qualified and quantified by HPAEC- PAD. Side groups of xylan1 and xylan2 were detected by FTIR. In the next step, xylan1 and xylan2 were exposed to two commercial endoxylanases namely veron 191 and pentopan mono BG. Temperature, pH, time, and enzyme dosage of hydrolyzation were optimized to maximize XOS and minimize xylose. The results showed that the enzymes successfully hydrolyzed xylan2 and produced XOS, but cannot hydrolyze xylan1. Pentopan mono BG and veron 191 produced the highest amount of XOS after 4 (1.17 mmol/g) and 6 hr (1.13 mmol/g) of incubation, respectively. Conversion factors of xylan2 to XOS for pentopan mono BG and veron were 0.41 and 0.36, respectively. This study presence the possible prebiotic properties of date seed XOS and its application in functional foods.

Enzymatically-synthesized xylo-oligosaccharides laurate esters as surfactants of interest

Lipase-catalyzed synthesis of xylo-oligosaccharides esters from pure xylobiose, xylotriose and xylotetraose in the presence of vinyl laurate was investigated. The influence of different experimental parameters such as the loading of lipase, the reaction duration or the use of a co-solvent was studied and the reaction conditions were optimized with xylobiose. Under the best conditions, a regioselective esterification occurred to yield a monoester with the acyl chain at the OH-4 of the xylose unit at the non-reducing end. Surface-active properties of these pure xylo-oligosaccharides fatty esters have been evaluated. They display interesting surfactant activities that differ according to the degree of polymerization (DP) of the glycone moiety.

A novel neutral and thermophilic endoxylanase from Streptomyces ipomoeae efficiently produced xylobiose from agricultural and forestry residues

Endoxylanases capable of producing high ratios of xylobiose from agricultural and forestry residues in neutral and high temperature conditions are attractive for the prebiotic and alternative sweetener industries. In this study, a putative glycosyl hydrolase gene from Streptomyces ipomoeae was cloned and expressed in Escherichia coli. The recombinant enzyme, named as SipoEnXyn10A, hydrolyzed beechwood xylan in endo-action mode releasing xylobiose as its main end product. It was most active at pH 6.5 and 75-80 °C and showed remarkable stability at 65 °C. The xylobiose yield from 10 g corncob and moso bamboo reached 1.123 ± 0.021 and 0.229 ± 0.005 g, respectively, at pH 6.5 and 70 °C, whichwas higher than other reports using the same material. Moreover, high ratios of xylobiose in the xylose-based product of about 85% were obtained from corncob, moso bamboo sawdust, cassava stem and Chinese fir sawdust. These results demonstrated that SipoEnXyn10A has potential for industrial application.

A sustainable process for procuring biologically active fractions of high-purity xylooligosaccharides and water-soluble lignin from Moso bamboo prehydrolyzate

BACKGROUND

Prehydrolyzate, which is from the prehydrolysis process in dissolving pulps industry, contains various sugar-derived and lignin compounds such as xylooligosaccharides (XOS), gluco-oligosaccharides, xylose, glucose, and soluble lignin (S-L). The XOS has several beneficial effects on human physiology. XOS and S-L in prehydrolyzate are difficult to efficiently fractionate due to their similar molecular weights and water solubility. In this work, we proposed a sustainable and green process using polystyrene divinylbenzene (PS-DVB) resin to simultaneously separate and recover XOS and S-L. Enzymatic hydrolysis with endo-1,4-β-xylanase and fermentation with P. stipites were sequentially applied to purify XOS to minimize xylose content as well as amplify contents of xylobiose and xylotriose. In addition, 2D-HSQC NMR was used to analyze the structural characteristics of XOS and S-L. Furthermore, the biological abilities of antioxidants and prebiotics of these fractions were investigated by scavenging radicals and cultivating intestinally beneficial bacterias, respectively.

RESULTS

Results showed that PS-DVB resin could simultaneously separate XOS and solubilized lignin with excellent yields of 93.2% and 85.3%, respectively. The obtained XOS after being purified by enzymatic hydrolysis and fermentation contained 57.7% of xylobiose and xylotriose. 10.4% amount of inherent xylan was found in the S-L fraction obtained by PS-DVB resin separation. 2D-HSQC NMR revealed that lignin carbohydrate complexes existed in both XOS and S-L as covalent linkages between lignin and 4-O-methylglucuronoarabinoxylan. The biological application results showed that the antioxidant capacity of S-L was stronger than XOS, while XOS was superior in promoting growth of intestinal Bifidobacteria adolescentis and stimulating production of short-chain fatty acids by Lactobacillus acidophilus.

CONCLUSIONS

The proposed strategy of sequentially combining hydrophobic resin separation, enzymatic hydrolysis, and fermentation was successfully demonstrated and resulted in simultaneous production of high-quality XOS and solubilized lignin. These biomass-derived products in prehydrolyzate can be regarded as value-adding prebiotics and antioxidants.

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.

The potential of tailoring the conditions of steam explosion to produce xylo-oligosaccharides from sugarcane bagasse

In this study, the potential of the steam explosion (SE) method to produce high levels XOS from sugarcane bagasse, a xylan-rich hemicellulosic feedstock, was assessed. The effect of different operating conditions on XOS production yield and selectivity were investigated using a mini-pilot scale SE unit. The results show that even under a non-optimized condition (190 °C, 5 min and 0.5% H₂SO₄ as catalyst), SE led to about 40% xylan recovery as XOS, which was comparable to the well-known, multi-step, enzymatic production of XOS from alkaline-extracted xylan, and other commonly employed chemical methods. In addition, the XOS-rich hydrolysate from SE constituted of greater diversity in the degree of polymerization, which has been shown to be desirable for prebiotic application.

XYLOOLIGOSACCHARIDES FROM AGRICULTURAL BY-PRODUCTS: CHARACTERISATION, PRODUCTION AND PHYSIOLOGICAL EFFECTS

The current study is a review of characteristics, production, physiological properties and application of xylooligosaccharides (XOS). XOS are the carbohydrates, their molecules are built from xylose residues linked mainly by в-(1→4)-glycoside bonds. Xylan is important for plant cell walls and is widely spread component in agricultural by-products. XOS are products of xylan hydrolytic degradation, and exhibiting the high prebiotic potential. The XOS preparation of wheat and rye bran stimulated the cells accumulation ‑ 1,4∙1010 CFU/cm3 of L. аcidophilus and 9,2∙1010 CFU/cm3 of В. bifidum. A difference in XOS molecules branching causes a wide range of their physiological properties: antioxidant, immunomodulation, antimicrobial, anti-inflammatory, anticarcinogenic. XOS can reduce high cholesterol level and triglycerides in blood plasma. XOS application reviewed in this article opens new perspectives on its potential use for human consumption. The rich sources of xylan are wheat, rye and barley bran, rice husk, wheat straw, corncobs, cotton stalk. Industrial way of XOS production includes chemical or enzymatic hydrolysis with following purification. Chemical methods are based on hydrothermal pretreatment and acidic or alkali extraction. Obtained oligosaccharides have a wide range of polymerization degree (DP) from 2 to 20. Enzymatic methods include fermentation with xylanase that allow controlling the XOS accumulation with certain DP. The different chromatographic purification after hydrolysis is used for analytical purposes. There are anion-exchange, size-exclusion, affinity, size-exclusion high-performance liquid chromatography. In addition, biomethods are preferred for XOS used in food, because such preparations do not contain monosaccharides and furfural as contaminants. XOS are stable in a wide range of temperature and pH, justifying the development of new synbiotics generation. Most widely XOS are used in production of functional products and pharmaceutical preparations. But they are also applied in cosmetic, agricultural and mixed feed industries.

Extraction of Glucuronoarabinoxylan from Quinoa Stalks (Chenopodium quinoa Willd.) and Evaluation of Xylooligosaccharides Produced by GH10 and GH11 Xylanases

Byproducts from quinoa are not yet well explored sources of hemicellulose or products thereof. In this work, xylan from milled quinoa stalks was retrieved to 66% recovery by akaline extraction using 0.5 M NaOH at 80 °C, followed by ethanol precipitation. The isolated polymer eluted as a single peak in size-exclusion chromatography with a molecular weight of >700 kDa. Analysis by Fourier transform infrared spectroscopy and nuclear magnetic resonance (NMR) combined with acid hydrolysis to monomers showed that the polymer was built of a backbone of β(1 → 4)-linked xylose residues that were substituted by 4-O-methylglucuronic acids, arabinose, and galactose in an approximate molar ratio of 114:23:5:1. NMR analysis also indicated the presence of α(1 → 5)-linked arabinose substituents in dimeric or oligomeric forms. The main xylooligosaccharides (XOs) produced after hydrolysis of the extracted glucuronoarabinoxylan polymer by thermostable glycoside hydrolases (GHs) from families 10 and 11 were xylobiose and xylotriose, followed by peaks of putative substituted XOs. Quantification of the unsubstituted XOs using standards showed that the highest yield from the soluble glucuronoarabinoxylan fraction was 1.26 g/100 g of xylan fraction, only slightly higher than the yield (1.00 g/100 g of xylan fraction) from the insoluble fraction (p < 0.05). No difference in yield was found between reactions in buffer or water (p > 0.05). This study shows that quinoa stalks represent a novel source of glucuronoarabinoxylan, with a substituent structure that allowed for limited production of XOs by GH10 or GH11 enzymes.

Xylanase production by Aureobasidium pullulans on globe artichoke stem: Bioprocess optimization, enzyme characterization and application in saccharification of lignocellulosic biomass

Statistical optimization of the factors affecting xylanase production by Aureobasidium pullulans NRRL Y-2311-1 on globe artichoke stem was performed for the first time. The optimization strategies used resulted in almost six-fold enhancement of xylanase production (66.48 U/ml). Biochemical and thermal characterization of the crude xylanase preparation was performed to elucidate its feasibility for different industrial applications. The optimum conditions for xylanase activity were pH 4.0 and 30-50°C. The enzyme was very stable over a wide pH range of 3.0-8.0. The thermal stability studies revealed an inactivation energy of 183 kJ/mol. Thermodynamic parameters (enthalpy, entropy, and Gibbs free energy) for thermal inactivation were also determined. Primary application of the crude xylanase preparation in saccharification of corn cob subjected to different pretreatment techniques has been evaluated. The crude xylanase preparation was very promising for saccharification of corn cob pretreated with aqueous ammonia. The maximum yield of reducing sugar was 357 mg/g dry substrate, which revealed that the crude xylanase from A. pullulans could be a very good alternative in saccharification of lignocellulosic biomass for biological fuel generation. This study also provides a basis for further exploitation of globe artichoke by-products in microbial production of several other industrially significant metabolites.

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%).

Biodegradation of lignin and nicotine with white rot fungi for the delignification and detoxification of tobacco stalk

BACKGROUND

Tobacco stalk is one kind of abundant crop residues in China. The high lignification of tobacco stalk increases its reusing cost and the existing of nicotine will cause serious pollution. The biodegradation of lignocellulosic biomass has been demonstrated to be an environmental and economical approach for the utilization of plant stalk. Meanwhile, many nicotine-degrading microorganisms were found in nature. However, microorganisms which could degraded both nicotine and lignin haven't been reported. Therefore, it's imperative to find some suitable microorganisms to break down lignin and simultaneously remove nicotine in tobacco stalk.

RESULTS

The nicotine in tobacco stalk could be degraded effectively by Trametes versicolor, Trametes hirsute and Phanerochaete chrysosporium. The nicotine content in tobacco stalk was lowered to below 500 mg/kg (a safe concentration to environment) after 10 days of fermentation with Phanerochaete chrysosporium and Trametes versicolor, and 15 days with Trametes hirsute. The degradation rate of lignin in the fermented tobacco stalk was 37.70, 51.56 and 53.75% with Trametes versicolor, Trametes hirsute and Phanerochaete chrysosporium, respectively. Meanwhile, 24.28% hemicellulose was degraded by Phanerochaete chrysosporium and 28.19% cellulose was removed by Trametes hirsute. Through the enzyme activity analysis, the main and highest ligninolytic enzymes produced by Phanerochaete chrysosporium, Trametes hirsute and Trametes versicolor were lignin peroxidase (88.62 U · L-1), manganese peroxidase (100.95 U · L-1) and laccase (745.65 U · L-1). Meanwhile, relatively high and stable cellulase activity was also detected during the fermentation with Phanerochaete chrysosporium, and the highest endoglucanase, exoglucanase and filter paper enzyme activities were 0.38 U · mL-1, 0.45 U · mL-1 and 0.35U · mL-1, respectively. Moreover, the products in the fermentation of tobacco stalk with P. chrysosporium were identified with GC-MS, besides the chemicals produced in the degradation of lignin and nicotine, some small molecular valuable chemicals and fatty acid were also detected.

CONCLUSIONS

Our study developed a new method for the degradation and detoxification of tobacco stalk by fermentation with white rot fungi Phanerochaete chrysosporium and Trametes hirsute. The different oxidative enzymes and chemical products detected during the degradation indicated a possible pathway for the utilization of tobacco stalk.

Development, validation and application of a hydrophilic interaction liquid chromatography-evaporative light scattering detection based method for process control of hydrolysis of xylans obtained from different agricultural wastes

Purified standards of xylooligosaccharides (XOSs) (DP2-6) were first prepared from a mixture of XOSs using solid phase extraction (SPE), followed by semi-preparative liquid chromatography both under hydrophilic interaction liquid chromatography (HILIC) modes. Then, an accurate quantitative analysis method based on hydrophilic interaction liquid chromatography-evaporative light scattering detection (HILIC-ELSD) was developed and validated for simultaneous determination of xylose (X1), xylobiose (X2), xylotriose (X3), xylotetraose (X4), xylopentaose (X5), and xylohexaose (X6). This developed HILIC-ELSD method was applied to the comparison of different hydrolysis methods for xylans and assessment of XOSs contents from different agricultural wastes. The result indicated that enzymatic hydrolysis was preferable with fewer by-products and high XOSs yield. The XOSs yield (48.40%) from sugarcane bagasse xylan was the highest, showing conversions of 11.21g X2, 12.75g X3, 4.54g X4, 13.31g X5, and 6.78g X6 from 100g xylan.