Acacia Xylan as a Substitute for Commercially Available Xylan and Its Application in the Production of Xylooligosaccharides

A novel thermophilic recombinant obligate xylobiohydrolase (AcGH30A) from Acetivibrio clariflavus orchestrates the deconstruction of xylan polysaccharides

GH30 xylobiohydrolases, an expanding enzyme category, need deeper insights for optimal use. The primary aim of this study was to characterize a new xylobiohydrolase, AcGH30A of GH30 family from Acetivibrio clariflavus. The gene encoding AcGH30A was cloned using pET28a(+) vector and expressed in E. coli BL21(DE3) cells. AcGH30A was purified by immobilized metal-ion affinity chromatography. SDS-PAGE analysis of AcGH30A showed molecular mass of ~58 kDa. AcGH30A showed optimum temperature 80 °C and optimum pH 7.0. AcGH30A was stable (maintaining >80 % of control activity) in pH range, 4-7 and temperature range, 30 °C -70 °C when incubated for 90 min. AcGH30A displayed melting temperature, 72 °C and half-life, 21 days at 4 °C. The enzyme activity of AcGH30A was enhanced by 10 mM Ca2+ and Mg2+ ions by 25 % and 21 %, respectively, whereas 10 mM Co2+, Zn2+, Fe2+, and Cu2+ ions significantly reduced it. AcGH30A showed activity against various xylan polysaccharides displaying highest Vmax, 139 U.mg-1 and KM, 0.71 mg.ml-1 against 4-O-methyl glucuronoxylan under optimum conditions. TLC, HPLC and LC-MS analyses of AcGH30A hydrolyzed products from xylan substrates revealed the release of sole product, xylobiose, confirming it as an obligate xylobiohydrolase. AcGH30A being a highly thermostable enzyme can be potentially utlilized in various biotechnological applications.

Extraction of cellulose from halophytic plants for the synthesis of a novel biocomposite

Cellulose nanofibers, a sustainable and promising material with widespread applications, exhibit appreciable strength and excellent mechanical and physicochemical properties. The preparation of cellulosic nanofibers from food or agricultural residue is not sustainable. Therefore, this study was designed to use three halophytic plants (Cressa cretica, Phragmites karka, and Suaeda fruticosa) to extract cellulose for the subsequent conversion to cellulosic nanofibers composites. The other extracted biomass components including lignin, hemicellulose, and pectin were also utilized to obtain industrially valuable enzymes. The maximum pectinase (31.56 IU mL-1), xylanase (35.21 IU mL-1), and laccase (15.89 IU mL-1) were produced after the fermentation of extracted pectin, hemicellulose, and lignin from S. fruticosa, P. karka, and C. cretica, respectively. Cellulose was methylated (with a degree of substitution of 2.4) and subsequently converted into a composite using polyvinyl alcohol. Scanning electron microscopy and Fourier-transform infrared spectroscopy confirmed the successful synthesis of the composites. The composites made up of cellulose from C. cretica and S. fruticosa had a high tensile strength (21.5 and 15.2 MPa) and low biodegradability (47.58% and 44.56%, respectively) after dumping for 3 months in soil, as compared with the composite from P. karka (98.79% biodegradability and 4.9 MPa tensile strength). Moreover, all the composites exhibited antibacterial activity against gram-negative bacteria (Escherichia coli and Klebsiella pneumoniae) and gram-positive bacteria (Staphylococcus aureus). Hence, this study emphasizes the possibility for various industrial applications of biomass from halophytic plants.

Evaluation of bamboo derived biochar as anode catalyst in microbial fuel cell for xylan degradation utilizing microbial co-culture

This study aimed to examine the microbial degradation of xylan through Bacillus sp. isolated from wastewater. Co-culture of Bacillus licheniformis strain and MTCC-8104 strain of Shewanella putrefaciens were employed in a microbial fuel cell (MFC) to facilitate energy production simultaneous xylan degradation under optimum conditions. Electrochemical properties of MFC and degradation analysis were used to validate xylan degradation throughout various experimental parameters. Degradation of the optimal xylan concentration using co-culture, resulting in a power density of 7.8 W/m3, the anode surface was modified with bamboo-derived biochar in order to increase power density under the same operational condition. Under optimum circumstances, increasing the anode's surface area boosted electron transport and electro-active biofilm growth, resulting in a higher power density of 12.9 W/m3. Co-culture of hydrolyzing and electro-active bacteria was found beneficial for xylan degradation and anode modifications enhance power output while microbial degradation.

Integrated Hemicellulose Extraction and Papermaking Fiber Production from Agro-Waste Biomass

The present study deals with the valorization of corn stalks in an integrated processing strategy targeting two products: extracted hemicelluloses (HC) and papermaking fibers. Preliminary trials were conducted to assess the individual or the combined effects of biomass treatment on the quality of the obtained hemicelluloses and papermaking fibers. Depending on the hot alkaline extraction (HAE) conditions, the extracted HC had a xylan content between 44-63%. The xylan removal yield ranged between 19-35%. The recovery of HC from the extraction liquor and final black liquor was significantly affected by process conditions. The experimental approach continued with the study of HAE conditions on the obtained paper's mechanical properties. The optimization approach considered conserving paper strength properties while achieving an equilibrium with the highest possible HC extraction yield. The optimal values are sodium hydroxide concentration (1%), process time (33 min), and temperature (100 °C). The xylan content in the separated HC sample was ~55%. An extended extraction of HC from the resulting pulp under hot alkaline conditions with 5% NaOH was performed to prove the HC influence on paper strength. The xylan content in HC samples was 65%. The consequence of xylan content reduction in pulp leads to 30-50% mechanical strength loss.

Hazelnut (Corylus avellana L.) shells as a potential source of dietary fibre: impact of hydrothermal treatment temperature on fibre structure and degradation compounds

BACKGROUND

Hemicellulose extraction from lignocellulosic biomasses has gained interest over the years, and hydrothermal treatment is one of the most common methods employed for this purpose. This work aimed to deeply study hazelnut (Corylus avellana L.) shells as a new source of dietary fibre, evaluating the effect of hydrothermal treatment temperatures on the type and structure of fibre extracted, but also on the formation of side-products derived from lignocellulose degradation.

RESULTS

Different process temperatures led to diverse polysaccharides in the hydrothermal extract. Pectin was identified for the first time in hazelnut shells when experimenting with extraction at 125 °C, whereas at 150 °C a heterogeneous mixture of pectin, xylan, and xylo-oligosaccharides was present. The highest yield in terms of total fibre was gained at 150 and 175 °C, and then decreased again at 200 °C. Finally, more than 500 compounds from different chemical classes were putatively identified and they appeared to be present in the extracted fibre with a different distribution and relative amount, depending on the heat treatment severity. A generally high content of phenols, phenyls, oligosaccharides, dehydro-sugars, and furans was observed.

CONCLUSIONS

Modulation of the hydrothermal treatment temperature allows fibre extracts with very different compositions, and therefore different potential end uses, to be obtained from hazelnut shells. A sequential temperature-based fractionation approach, as a function of the severity of the extraction parameters, can also be considered. Nevertheless, the study of the side-compounds formed from lignocellulosic matrix degradation, as a function of the applied temperature, needs to be fully addressed for a safe introduction of the fibre extract within the food chain. © 2023 The Authors. Journal of The Science of Food and Agriculture published by John Wiley & Sons Ltd on behalf of Society of Chemical Industry.

Synthesis of methylcellulose-polyvinyl alcohol composite, biopolymer film and thermostable enzymes from sugarcane bagasse

Agro-industrial wastes and by-products are the natural and abundant resources of biomaterials to obtain various value-added items such as biopolymer films, bio-composites and enzymes. This study presents a way to fractionate and to convert an agro-industrial residue, sugarcane bagasse (SB), into useful materials with potential applications. Initially cellulose was extracted from SB which was then converted into methylcellulose. The synthesized methylcellulose was characterized by scanning electron microscopy and FTIR. Biopolymer film was prepared by using methylcellulose, polyvinyl alcohol (PVA), glutaraldehyde, starch and glycerol. The biopolymer was characterized to exhibit 16.30 MPa tensile strength, 0.05 g/m² h of water vapor transmission rate, 366 % of water absorption to its original weight after 115 min of immersion, 59.08 % water solubility, 99.05 % moisture retention capability and 6.01 % of moisture absorption after 144 h. Furthermore, in vitro studies on absorption and dissolution of model drug by biopolymer showed 2.04 and 104.59 % of swelling ratio and equilibrium water content, respectively. Biocompatibility of the biopolymer was checked by using gelatin media and it was observed that swelling ratio was higher in initial 20 min of contact. The extracted hemicellulose and pectin from SB were fermented by a thermophilic bacterial strain, Neobacillus sedimentimangrovi UE25 that yielded 12.52 and 6.4 IU mL^-1 of xylanase and pectinase, respectively. These industrially important enzymes further augmented the utility of SB in this study. Therefore, this study emphasizes the possibility for industrial application of SB to form various products.

Xylans extracted from branches and leaves of Protium puncticulatum: antioxidant, cytotoxic, immunomodulatory, anticoagulant, antitumor, prebiotic activities and their structural characterization

This work aimed to isolate and characterize xylans from branches and leaves of Protium puncticulatum, in addition to evaluating its in vitro biological and prebiotic potential. The results showed that the chemical structure of the obtained polysaccharides is similar being classified as homoxylans. The xylans presented an amorphous structure, in addition to being thermally stable and presenting a molecular weight close to 36 g/mol. With regard to biological activities, it was observed that xylans were able to promote low antioxidant activity (< 50%) in the different assays evaluated. The xylans also showed no toxicity against normal cells, in addition to being able to stimulate cells of the immune system and showing promise as anticoagulant agents. In addition to presenting promising antitumor activity in vitro. In assays of emulsifying activity, xylans were able to emulsify lipids in percentages below 50%. Regarding in vitro prebiotic activity, xylans were able to stimulate and promote the growth of different probiotics. Therefore, this study, in addition to being a pioneer, contributes to the application of these polysaccharides in the biomedical and food areas.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-023-03506-1.

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.

Two-Step Saccharification of the Xylan Portion of Sugarcane Waste by Recombinant Xylanolytic Enzymes for Enhanced Xylose Production

Sugarcane bagasse (SB) and sugarcane trash (SCT) containing 30% hemicellulose content are the waste from the sugarcane industry. Hemicellulose being heterogeneous, more complex, and less abundant than cellulose remains less explored. The optimized conditions for the pretreatment of SB and SCT for maximizing the delignification are soaking in aqueous ammonia (SAA), 18.5 wt %, followed by heating at 70 °C for 14 h. The optimization of hydrolysis of SAA pretreated (ptd) SB and SCT by the Box-Behnken design in the first step of saccharification by xylanase (CtXyn11A) and α-l-arabinofuranosidase (PsGH43_12) resulted in the total reducing sugar (TRS) yield of xylooligosaccharides (TRS_(XOS)) of 93.2 mg/g ptd SB and 85.1 mg/g ptd SCT, respectively. The second step of saccharification by xylosidase (BoGH43) gave the TRS yield of 164.7 mg/g ptd SB and 147.2 mg/g ptd SCT. The high-performance liquid chromatography analysis of hydrolysate obtained after the second step of saccharification showed 69.6% xylan-to-xylose conversion for SB and 64.1% for SCT. This study demonstrated the optimization of the pretreatment method and of the enzymatic saccharification by recombinant xylanolytic enzymes, resulting in the efficient saccharification of ptd hemicellulose to TRS by giving 73.5% conversion for SB and 71.1% for SCT. These optimized conditions for the pretreatment and saccharification of sugarcane waste can also be used at a large scale.

Extraction and characterization of xylan from sugarcane tops as a potential commercial substrate

Xylan is the major hemicellulose present in sugarcane stem secondary cell walls. Xylan is composed of xylose backbone with a high degree of substitutions, which affects its properties. In the present study, the xylan from sugarcane tops (SCT) was extracted and characterized. Compositional analysis of xylan extracted from SCT (SCTx) displayed the presence of 74% of d-xylose residues, 16% of d-glucuronic acid residues and 10% of l-arabinose. High performance size exclusion chromatographic analysis of SCTx displayed a single peak corresponding to a molecular mass of ∼57 kDa. The Fourier transform infrared spectroscopic analysis of SCTx displayed the peaks corresponding to those obtained from commercial xylan. FESEM analysis of SCTx showed the granular and porous surface structure. Differential thermogravimetric analysis (DTG) of SCTx displayed two thermal degradation temperatures (T_d) of 228°C, due to breakdown of the side chains of glucuronic acid and arabinose and 275°C, due to breakdown of xylan back bone. The presence of arabinose and glucuronic acid as a side chains was confirmed by the DTG and thermogravimetric analysis. The CHNS analysis of SCTx showed the presence of only carbon and hydrogen supporting its purity. The recombinant xylanase (CtXyn11A) from Clostridium thermocellum displayed a specific activity of 1394 ± 51 U/mg with SCTx, which was higher than those with commercial xylans. The thin layer chromatography and electrospray ionization mass spectroscopy analyses of CtXyn11A hydrolysed SCTx contained a series of linear xylo-oligosaccharides ranging from degree of polymerization 2-6 and no substituted xylo-oligosaccharides because of the endolytic activity of enzyme. The extracted xylan from SCT can be used as an alternative commercial substrate and for oligo-saccharide production.