A novel glycoside hydrolase 43-like enzyme from Clostridium boliviensis is an endo-xylanase and a candidate for xylooligosaccharide production from different xylan substrates

An uncharacterized gene encoding a glycoside hydrolase family 43-like enzyme from Clostridium boliviensis strain E-1 was identified from genomic sequence data, and the encoded enzyme, CbE1Xyn43-l, was produced in Escherichia coli. CbE1Xyn43-l (52.9 kDa) is a two-domain endo-β-xylanase consisting of a C-terminal CBM6 and a GH43-like catalytic domain. The positions of the catalytic dyad conserved in GH43, the catalytic base (Asp74), and proton donor (Glu240) were identified in alignments including GH43-enzymes of known 3D-structure from different subfamilies. CbE1Xyn43-l is active at pH 7.0-9.0, with optimum temperature at 65°C, and a more than 7 days' half-life in irreversible deactivation studies at this temperature. The enzyme hydrolyzed birchwood xylan, quinoa stalks glucuronoarabinoxylan, and wheat arabinoxylan with xylotriose and xylotetraose as major hydrolysis products. CbE1Xyn43-l also released xylobiose from pNPX2 with low turnover (kcat of 0.044 s-1) but was inactive on pNPX, showing that a degree of polymerization of three (DP3) was the smallest hydrolyzable substrate. Divalent ions affected the specific activity on xylan substrates, which dependent on the ion could be increased or decreased. In conclusion, CbE1Xyn43-l from C. boliviensis strain E-1 is the first characterized member of a large group of homologous hypothetical proteins annotated as GH43-like and is a thermostable endo-xylanase, producing xylooligosaccharides of high DP (xylotriose and xylotetraose) producer.

IMPORTANCE

The genome of Clostridium boliviensis strain E-1 encodes a number of hypothetical enzymes, annotated as glycoside hydrolase-like but not classified in the Carbohydrate Active Enzyme Database (CAZy). A novel thermostable GH43-like enzyme is here characterized as an endo-β-xylanase of interest in the production of prebiotic xylooligosaccharides (XOs) from different xylan sources. CbE1Xyn43-l is a two-domain enzyme composed of a catalytic GH43-l domain and a CBM6 domain, producing xylotriose as main XO product. The enzyme has homologs in many related Clostridium strains which may indicate a similar function and be a previously unknown type of endo-xylanase in this evolutionary lineage of microorganisms.

Are phenolic compounds produced during the enzymatic production of prebiotic xylooligosaccharides (XOS) beneficial: a review

Phenolics produced during xylooligosaccharide production might inhibit xylanases and enhance the antioxidant and antimicrobial activities of XOS. The effects of phenolic compounds on xylanases may depend on the type and concentration of the compound, the plant biomass used, and the enzyme used. Understanding the effects of phenolic compounds on xylanases and their impact on XOS is critical for developing viable bioconversion of lignocellulosic biomass to XOS. Understanding the complex relationship between phenolic compounds and xylanases can lead to the development of strategies that improve the efficiency and cost-effectiveness of XOS manufacturing processes and optimise enzyme performance.

Physicochemical and Sensory Stability Evaluation of Gummy Candies Fortified with Mountain Germander Extract and Prebiotics

Health-conscious consumers seek convenient ways of incorporating different functional ingredients into their diets. Gummy candies are among the most popular confectionery products but generally regarded as nutritionally empty. A gelatin-sugar matrix, providing a highly appreciated sensory experience of sweetness and chewiness, could be used to deliver various bioactive compounds, especially those carrying an unpleasant taste. This work aimed to formulate gelatin gummies based on the mountain germander extract (MGe) as a source of phenylethanoid glycosides (PhEG). Sucrose and glucose syrup contents were partially or completely substituted with combinations of xylitol, maltitol and prebiotic poly- and oligosaccharides. Chemical, textural and sensory parameters were evaluated after production and 2 months of storage. Formulations containing fructooligosaccharides and xylooligosaccharides maintained a characteristic appearance during storage at all three levels of sugar (high, low and none), whereas inulin-added and plain (i.e., without prebiotic) candies suffered from mold contamination or appearance/textural changes. The color of the candies noticeably changed and appeared darker. The PhEG were shown to be stable during the candies' production (approximately 90%) and generally maintained their contents during storage. Texture parameters, except hardness, exhibited high positive correlations and resembled the commercial product. Sensory-wise, a moderate bitterness intensity with a decreasing tendency, along with the high transparency and preservation of the characteristic shape facilitated high general acceptance. Gummy candies with prebiotics were shown to be a highly suitable matrix for the bitter MGe, delivering up to 40 mg of PhEG and 4.5 g of prebiotics in one serving size. This study provides a reference for implementing herbal extracts and emerging prebiotics (XOS) in functional confectionery.

Optimization of Xylooligosaccharides Production by Native and Recombinant Xylanase Hydrolysis of Chicken Feed Substrates

Poultry production faces several challenges, with feed efficiency being the main factor that can be influenced through the use of different nutritional strategies. Xylooligosaccharides (XOS) are functional feed additives that are attracting growing commercial interest due to their excellent ability to modulate the composition of the gut microbiota. The aim of the study was to apply crude and purified fungal xylanases, from Trichoderma harzianum, as well as a recombinant glycoside hydrolase family 10 xylanase, derived from Geobacillus stearothermophilus T6, as additives to locally produced chicken feeds. A Box-Behnken Design (BBD) was used to optimize the reducing sugar yield. Response surface methodology (RSM) revealed that reducing sugars were higher (8.05 mg/mL, 2.81 mg/mL and 2.98 mg/mL) for the starter feed treated with each of the three enzymes compared to the treatment with grower feed (3.11 mg/mL, 2.41 mg/mL and 2.62 mg/mL). The hydrolysis products were analysed by thin-layer chromatography (TLC), and high-performance liquid chromatography (HPLC) analysis and showed that the enzymes hydrolysed the chicken feeds, producing a range of monosaccharides (arabinose, mannose, glucose, and galactose) and XOS, with xylobiose being the predominant XOS. These results show promising data for future applications as additives to poultry feeds.

Xylanase Production by Solid-State Fermentation for the Extraction of Xylooligosaccharides from Soybean Hulls§

Research background

The development of a novel process for the production of xylooligosaccharides (XOS) based on the 4R concept is made possible by the integration of numerous techniques, especially enzymatic modification together with the physical pretreatment of renewable materials. This study aims to integrate the use of agricultural wastes for the production of xylanase by a new strain of Penicillium sp. and value-added products, XOS.

Experimental approach

For the production of xylanase, a solid-state fermentation was performed using wheat bran as substrate. To obtain the most active crude extract of xylanase, the time frame of cultivation was first adjusted. Then, the downstream process for xylanase purification was developed by combining different membrane separation units with size exclusion chromatography. Further characterisation included determination of the optimal pH and temperature, determination of the molecular mass of the purified xylanase and analysis of kinetic parameters. Subsequently, the hydrolytic ability of the partially purified xylanase in the hydrolysis of alkali-extracted hemicellulose from soybean hulls was investigated.

Results and conclusions

Our results show that Penicillium rubens produced extracellular xylanase at a yield of 21 U/g during solid-state fermentation. Using two ultrafiltration membranes of 10 and 3 kDa in combination with size exclusion chromatography, a yield of 49 % and 13-fold purification of xylanase was achieved. The purified xylanase (35 kDa) cleaved linear bonds β-(1→4) in beechwood xylan at a maximum rate of 0.64 μmol/(min·mg) and a Michaelis constant of 44 mg/mL. At pH=6 and 45 °C, the purified xylanase showed its maximum activity. The xylanase produced showed a high ability to hydrolyse the hemicellulose fraction isolated from soybean hulls, as confirmed by thin-layer chromatography. In the hydrothermally pretreated hemicellulose hydrolysate, the content of XOS with different degrees of polymerisation was detected, while in the non-pretreated hemicellulose hydrolysate, the content of xylotriose and glucose was confirmed.

Novelty and scientific contribution

Future research focusing on the creation of new enzymatic pathways for use in processes to convert renewable materials into value-added products can draw on our findings.

A prebiotic diet modulates the oral microbiome composition and results in the attenuation of oropharyngeal candidiasis in mice

Oral bacteria can influence the ability of Candida albicans to cause oropharyngeal candidiasis (OPC). We recently reported that a Lactobacillus johnsonii-enriched oral microbiota reduced C. albicans virulence in an immunosuppressed OPC mouse model. As a follow-up, in this work, we aimed to enrich the resident oral Lactobacillus communities with a prebiotic diet to further assess their effect on the severity of OPC. We tested the effect of a prebiotic xylo-oligosaccharides (XOS)-enriched diet in the oral global bacterial composition and severity of OPC. We assessed changes in the oral microbiome composition via 16S-rRNA gene high-throughput sequencing, validated by qPCR. The impact of the prebiotic diet on Candida infection was assessed by quantifying changes in oral fungal and bacterial biomass and scoring tongue lesions. Contrary to expectations, oral Lactobacillus communities were not enriched by the XOS-supplemented diet. Yet, XOS modulated the oral microbiome composition, increasing Bifidobacterium abundance and reducing enterococci and staphylococci. In the OPC model, the XOS diet attenuated Candida virulence and bacterial dysbiosis, increasing lactobacilli and reducing enterococci on the oral mucosa. We conclude that XOS attenuates Candida virulence by promoting a bacterial microbiome structure more resilient to Candida infection. IMPORTANCE This is the first study on the effects of a prebiotic diet on the oral mucosal bacterial microbiome and an oropharyngeal candidiasis (OPC) mouse model. We found that xylo-oligosaccharides change the oral bacterial community composition and attenuate OPC. Our results contribute to the understanding of the impact of the oral bacterial communities on Candida virulence.

How Do Prebiotics Affect Human Intestinal Bacteria?-Assessment of Bacterial Growth with Inulin and XOS In Vitro

Prebiotics are believed to exhibit high specificity in stimulating the growth or activity of a limited number of commensal microorganisms, thereby conferring health benefits to the host. However, the mechanism of action of prebiotics depends on multiple factors, including the composition of an individual's gut microbiota, and is therefore difficult to predict. It is known that different bacteria can utilize inulin and xylooligosaccharides (XOS), but an overview of which bacteria in the human gut may be affected is lacking. Detailed knowledge of how bacterial growth is affected by prebiotics is furthermore useful for the development of new synbiotics, which combine a living microorganism with a selective substrate to confer a health benefit to the host. Hence, we developed a statistical model to compare growth in vitro among typical human gut bacteria from different phylogenetic lineages. Based on continuous observation of the optical density (OD600), we compare maximal growth rates (rmax), maximal attained OD600 (ODmax), and area under the growth curve (AUC) of bacteria grown on inulin or XOS. The consideration of these three parameters suggests strain-specific preferences for inulin or XOS and reveals previously unknown preferences such as Streptococcus salivarius growth on XOS.

Feeding Behavior, Growth Performance and Meat Quality Profile in Broiler Chickens Fed Multiple Levels of Xylooligosaccharides

A total of 240 1-day-old Arbor Acres broiler chickens were randomly distributed to 4 treatment groups with 6 replicates and 10 birds per replicate. Chickens were fed with corn-soybean meal diet supplementation with additions of 0, 150, 300, and 450 mg/kg XOS for 42 days. At 4 weeks of age, the average feeding time was reduced in the 450 mg/kg XOS group (p < 0.05), and the percentage of feeding time was increased in the 300 mg/kg XOS group (p < 0.05). At 5 weeks of age, broilers fed with 300 mg/kg XOS had increased the percentage of feeding time (p < 0.05), and 450 mg/kg XOS had increased the feeding frequency and percentage of feeding time (p < 0.05). At 6 weeks of age, the feeding frequency was highest in the 450 mg/kg XOS group (p < 0.05). During 4 to 6 weeks of age, the average feeding time was increased in 300 mg/kg XOS group (p < 0.05), the frequency was improved in the 450 mg/kg XOS group (p < 0.05), and the percentage of feeding time was longer in the XOS group than that in the control group (p < 0.05). The average daily gain was improved during days 22-42 and days 1-42 in the 150 mg/kg XOS group (p < 0.05). Broilers fed with 300 mg/kg XOS had an increased eviscerated rate (p < 0.05). The pH45min of breast muscle was highest in the 450 mg/kg XOS group (p < 0.05), as well as the pH45min and pH24h of thigh muscle, which improved in the 300 mg/kg and 450 mg/kg XOS groups (p < 0.05). In addition, the cooking loss of thigh muscle was reduced in the 300 mg/kg XOS group (p < 0.05). In conclusion, dietary supplementation with XOS had positive effects on the feeding behavior, growth performance, and meat quality of broiler chickens.

Xylooligosaccharides: A Bibliometric Analysis and Current Advances of This Bioactive Food Chemical as a Potential Product in Biorefineries' Portfolios

Xylooligosaccharides (XOS) are nondigestible compounds of great interest for food and pharmaceutical industries due to their beneficial prebiotic, antibacterial, antioxidant, and antitumor properties. The market size of XOS is increasing significantly, which makes its production from lignocellulosic biomass an interesting approach to the valorization of the hemicellulose fraction of biomass, which is currently underused. This review comprehensively discusses XOS production from lignocellulosic biomass, aiming at its application in integrated biorefineries. A bibliometric analysis is carried out highlighting the main players in the field. XOS production yields after different biomass pretreatment methods are critically discussed using Microsoft PowerBI® (2.92.706.0) software, which involves screening important trends for decision-making. Enzymatic hydrolysis and the major XOS purification strategies are also explored. Finally, the integration of XOS production into biorefineries, with special attention to economic and environmental aspects, is assessed, providing important information for the implementation of biorefineries containing XOS in their portfolio.

The Potential of Xylooligosaccharides as Prebiotics and Their Sustainable Production from Agro-Industrial by-Products

In recent years, concerns about a good-quality diet have increased. Food supplements such as prebiotics have great nutritional and health benefits. Within the diverse range of prebiotics, xylooligosaccharides (XOs) show high potential, presenting exceptional properties for the prevention of systemic disorders. XOs can be found in different natural sources; however, their production is limited. Lignocellulosic biomasses present a high potential as a source of raw material for the production of XOs, making the agro-industrial by-products the perfect candidates for production on an industrial scale. However, these biomasses require the application of physicochemical pretreatments to obtain XOs. Different pretreatment methodologies are discussed in terms of increasing the production of XOs and limiting the coproduction of toxic compounds. The advance in new technologies for XOs production could decrease their real cost (USD 25-50/kg) on an industrial scale and would increase the volume of market transactions in the prebiotic sector (USD 4.5 billion). In this sense, new patents and innovations are being strategically developed to expand the use of XOs as daily prebiotics.

Hydrothermal pretreatment for the production of prebiotic oligosaccharides from tobacco stem

Tobacco stem is an abundant and inexpensive renewable source to produce prebiotics by circular economy. In this study, hydrothermal pretreatments were evaluated on the release of xylooligosaccharides (XOS) and cello-oligosaccharides (COS) from the tobacco stem by a central composite rotational design associated with response surface methodology to evaluate the effects of temperature (161.72 to 218.3 °C) and solid load (SL) (2.93 to 17.07%). XOS were the main compounds released to the liquor. Desirability function was performed to maximize the production of XOS and minimize the effects of release of monosaccharides and degradation compounds. The result indicated yield of 96% w[XOS]/w[xylan] for 190 °C-2.93% SL. The highest value for COS and total oligomers content (COS + XOS) was 6.42 g/L and 17.7 g/L, respectively, for 190 °C-17.07% SL. The mass balance for the best yield XOS condition predicted 132 kg of XOS (X2-X6) from 1000 kg of tobacco stem.

In Vitro Assessment of the Prebiotic Potential of Xylooligosaccharides from Barley Straw

Barley straw was subjected to hydrothermal pretreatment (steam explosion) processing to evaluate its potential as a raw material to produce xylooligosaccharides (XOS) suitable for use as a prebiotic. The steam explosion pretreatment generated a liquid fraction containing solubilised hemicellulose. This fraction was purified using gel permeation chromatography to obtain a fraction rich in XOS DP2-DP6. The sample was characterised through analytical techniques such as HPAEC-PAD, FTIR and MALDI-TOF-MS. The prebiotic activity was evaluated using in vitro fermentation in human faecal cultures through the quantification of short-chain fatty acid (SCFA) and lactate production, the evolution of the pH and the consumption of carbon sources. The total SCFA production at the end of fermentation (30 h) was 90.1 mM. Positive significant differences between the amount of XOS from barley straw and fructooligosaccharides after incubation were observed.

Immobilization and Application of the Recombinant Xylanase GH10 of Malbranchea pulchella in the Production of Xylooligosaccharides from Hydrothermal Liquor of the Eucalyptus (Eucalyptus grandis) Wood Chips

Xylooligosaccharides (XOS) are widely used in the food industry as prebiotic components. XOS with high purity are required for practical prebiotic function and other biological benefits, such as antioxidant and inflammatory properties. In this work, we immobilized the recombinant endo-1,4-β-xylanase of Malbranchea pulchella (MpXyn10) in various chemical supports and evaluated its potential to produce xylooligosaccharides (XOS) from hydrothermal liquor of eucalyptus wood chips. Values >90% of immobilization yields were achieved from amino-activated supports for 120 min. The highest recovery values were found on Purolite (142%) and MANAE-MpXyn10 (137%) derivatives, which maintained more than 90% residual activity for 24 h at 70 °C, while the free-MpXyn10 maintained only 11%. In addition, active MpXyn10 derivatives were stable in the range of pH 4.0−6.0 and the presence of the furfural and HMF compounds. MpXyn10 derivatives were tested to produce XOS from xylan of various sources. Maximum values were observed for birchwood xylan at 8.6 mg mL−1 and wheat arabinoxylan at 8.9 mg mL−1, using Purolite-MpXyn10. Its derivative was also successfully applied in the hydrolysis of soluble xylan present in hydrothermal liquor, with 0.9 mg mL−1 of XOS after 3 h at 50 °C. This derivative maintained more than 80% XOS yield after six cycles of the assay. The results obtained provide a basis for the application of immobilized MpXyn10 to produce XOS with high purity and other high-value-added products in the lignocellulosic biorefinery field.

Glutamic acid assisted hydrolysis strategy for preparing prebiotic xylooligosaccharides

Since the immune-boosting properties as well as the benefit of promoting the growth of gut bacteria, xylooligosaccharides as prebiotics have attracted considerable interest as functional feed additives around the world. A growing number of studies suggest that acidic hydrolysis is the most cost-effective method for treating xylan materials to prepare xylooligosaccharides, and organic acids were proved to be more preferable. Therefore, in this study, glutamic acid, as an edible and nutritive organic acid, was employed as a catalyst for hydrolyzing xylan materials to prepare xylooligosaccharides. Further, xylooligosaccharide yields were optimized using the response surface methodology with central composite designs. Through the response surface methodology, 28.2 g/L xylooligosaccharides with the desirable degree of polymerization (2-4) at a yield of 40.5 % could be achieved using 4.5% glutamic acid at 163°C for 41 min. Overall, the application of glutamic acid as a catalyst could be a potentially cost-effective method for producing xylooligosaccharides.

A sustainable process for co-production of xylooligosaccharides and ethanol from alkali treated sugarcane bagasse: A strategy towards waste management

Present study aims at sustainable utilization of sugarcane bagasse (SCB) for production of valuable prebiotic xylooligosaccharides (XOS) along with second generation ethanol. Fractionation of SCB into hemicellulose rich liquid fraction and cellulose rich solid residue was achieved using alkaline treatment. Carbohydrate rich precipitate obtained from liquid fraction was utilized for XOS production using inhouse produced endoxylanase. XOS production from SCB xylan was optimized by employing response surface methodology. Under optimized conditions, maximum XOS yield was 227.72 mg/g of carbohydrate rich precipitates. The solid residue obtained after alkaline pretreatment was used for ethanol fermentation by prehydrolysis and simultaneous saccharification and fermentation (P-SSF) process using cellulolytic enzyme cocktail and Saccharomyces cerevisiae SM1. Maximum ethanol concentration, productivity and yield were 79.76 ± 0.16 g/L, 0.83 g/L/h and 69.38%, respectively by employing P-SSF process. Based on the experimental data it can be predicted that bioconversion of 100 g raw SCB can yield 6.26 g of XOS (DP 2-DP 5), 15.95 g ethanol and 1.44 g of xylitol. Present investigation reports an integrated process for effective bioconversion of SCB into value added products by maximum utilization of cellulosic and hemicellulosic fractions simultaneously using indigenously produced fungal enzymes.

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

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

Structural and Biochemical Characterization of a Nonbinding SusD-Like Protein Involved in Xylooligosaccharide Utilization by an Uncultured Human Gut Bacteroides Strain

In the human gut microbiota, Bacteroidetes break down dietary and endogenous glycosides through highly specific polysaccharide utilization loci (PULs). PULs encode a variety of sensor regulators, binding proteins, transporters, and carbohydrate-active enzymes (CAZymes). Surface glycan-binding proteins (SGBPs) are essential for the efficient capture of the glycosides present on the cell surface, providing Bacteroidetes with a competitive advantage in colonizing their habitats. Here, we present the functional and structural characterization of a SusD-like protein encoded by a xylooligosaccharide (XOS) PUL from an uncultured human gut Bacteroides strain. This locus is also conserved in Bacteroides vulgatus, thereby providing new mechanistic insights into the role of SGBPs in the metabolism of dietary fiber of importance for gut health. Various in vitro analyses, including saturation transfer difference nuclear magnetic resonance (STD-NMR) spectroscopy, revealed that the SusD-like protein cannot bind to the cognate substrate of the XOS PUL, although its presence is essential for the PUL to function. Analysis of the crystal structure of the SusD-like protein reveals an unfolded binding surface and the absence or inappropriate orientation of several key residues compared with other known SusD-like structures. These results highlight the critical role of the SusD-like protein in the transport of oligosaccharides and provide fundamental knowledge about the structure-function of SusC/D-like transporters, revealing that the binding specificity of SusD-like SGBPs does not necessarily reflect the uptake specificity of the transporter.

IMPORTANCE The metabolization of dietary fiber is a crucial function for many gut bacteria, especially Bacteroidetes, which are particularly well adapted for recognizing, binding, transporting, and degrading glycosides. In this study, we report the functional and structural characterization of a SusD-like protein involved in xylooligosaccharide utilization by an uncultured gut Bacteroides strain. We demonstrate that while this protein is structurally similar to many canonical Bacteroidetes surface glycan-binding proteins, it cannot bind the substrate taken up by the cognate SusC-like transporter. This lack of binding might be explained by the absence of several key residues known to be involved in oligosaccharide binding and/or the possible necessity of the SusC-like protein to be present to create a cooperative binding site. The term “surface glycan-binding proteins” generally used for SusD-like proteins is thus not generic. Overall, this study allowed us to revisit the concept of glycoside utilization by Bacteroidetes, in particular those strains that feed on the short fibers naturally present in some dietary compounds or on the leftovers of other microbes.

Biochemical and Thermodynamic Studies on a Novel Thermotolerant GH10 Xylanase from Bacillus safensis

Xylanases have a broad range of applications in agro-industrial processes. In this study, we report on the discovery and characterization of a new thermotolerant GH10 xylanase from Bacillus safensis, designated as BsXyn10. The xylanase gene (bsxyn10) was cloned from Bacillus safensis and expressed in Escherichia coli. The reduced molecular mass of BsXyn10 was 48 kDa upon SDS-PAGE. Bsxyn10 was optimally active at pH 7.0 and 60 °C, stable over a broad range of pH (5.0–8.0), and also revealed tolerance toward different modulators (metal cations, EDTA). The enzyme was active toward various xylans with no activity on the glucose-based polysaccharides. K_M, v_max, and k_cat for oat spelt xylan hydrolysis were found to be 1.96 g·L⁻¹, 58.6 μmole·min⁻¹·(mg protein)⁻¹, and 49 s⁻¹, respectively. Thermodynamic parameters for oat spelt xylan hydrolysis at 60 °C were ΔS* = −61.9 J·mol⁻¹·K⁻¹, ΔH* = 37.0 kJ·mol⁻¹ and ΔG* = 57.6 kJ·mol⁻¹. BsXyn10 retained high levels of activity at temperatures up to 60 °C. The thermodynamic parameters (ΔH*_D, ΔG*_D, ΔS*_D) for the thermal deactivation of BsXyn10 at a temperature range of 40–80 °C were: 192.5 ≤ ΔH*_D ≤ 192.8 kJ·mol⁻¹, 262.1 ≤ ΔS*_D ≤ 265.8 J·mol⁻¹·K⁻¹, and 99.9 ≤ ΔG*_D ≤ 109.6 kJ·mol⁻¹. The BsXyn10-treated oat spelt xylan manifested the catalytic release of xylooligosaccharides of 2–6 DP, suggesting that BsXyn10 represents a promising candidate biocatalyst appropriate for several biotechnological applications.

Application of oligosaccharides in meat processing and preservation

In recent decades, consumer preference and attention to foodstuff presented as healthy and with desirable nutritional information, has increased significantly. In this field, the meat industry has a challenging task since meat and meat products have been related to various chronic diseases. Functional ingredients have emerged in response to the increasing demand for healthier and more nutritious foods. On this matter, oligosaccharides such as fructooligosaccharides (FOS), xylooligosaccharides (XOS), galactooligosaccharides (GOS), and chitooligosaccharides (COS) have been presented as suitable ingredients for the meat industry with the aim of obtaining healthier meat derivatives (e.g. with low fat or sugar content, reduced amount of additives, and desirable functional properties, etc.). However, studies considering application of such oligomers in the meat sector are scarce. In addition, a large number of issues remain to be solved related both to obtaining and characterizing the oligosaccharides available in the industry and to the effect that these ingredients have on the features of meat products (mainly physicochemical and sensory). The study of new oligosaccharides, the methodologies for obtaining them, and their application to new meat products should be promoted, as well as improving knowledge about their effects on the properties of functional meat foods.

Characterization of a New Xylanase Found in the Rumen Metagenome and Its Effects on the Hydrolysis of Wheat

Wheat is the main ingredient of poultry diet, but its xylan has an adverse impact on poultry production. A novel xylanase from beef cattle rumen metagenome (RuXyn) and its effect on the wheat hydrolysis were investigated in the present study. The RuXyn coded for 377 amino acids and exhibited low identity (<40%) to previously reported proteins. The RuXyn was heterologously expressed in Escherichia coli and showed maximum activity at pH 6.0 and 40 °C. The activity of RuXyn could be increased by 79.8 and 36.0% in the presence of Ca²⁺ and Tween 20, respectively. The soluble xylan and insoluble xylan in wheat could be effectively degraded by RuXyn and xylooligosaccharides produced accounting for more than 80% of the products. This study demonstrates that RuXyn has substantial potential to improve the application of wheat in poultry production by degrading wheat xylan and the accompanying xylooligosaccharides produced.

Effects of Xylooligosaccharides on Lipid Metabolism, Inflammation, and Gut Microbiota in C57BL/6J Mice Fed a High-Fat Diet

Xylooligosaccharide (XOS) is a source of prebiotics with multiple biological activities. The present study aimed to investigate the effects of XOS on mice fed a high-fat diet. Mice were fed either a normal diet or a high-fat diet supplemented without or with XOS (250 and 500 mg/kg), respectively, for 12 weeks. The results showed that the XOS inhibited mouse weight gain, decreased the epididymal adipose index, and improved the blood lipid levels, including triglyceride (TG), total cholesterol (TC), and low-density lipoprotein cholesterol (LDL-C) levels. Moreover, XOS reduced the activity of alanine aminotransferase (ALT) and aspartate aminotransferase (AST), and alleviated the damage to the liver caused by the high-fat diet. XOS also reduced hyperlipidemia-associated inflammatory responses. Additionally, quantitative real-time polymerase chain reaction results showed that XOS intervention activated the AMP-activated protein kinase (AMPK) pathway to regulate the fat synthesis, decomposition, and β oxidation; upregulated the mRNA expression levels of carnitine palmitoyl transferase 1 (CPT-1), peroxisome proliferator-activated receptors α (PPAR-α), and cholesterol 7-alpha hydroxylase (CYP7A1); and downregulated the mRNA expression levels of acetyl-CoA carboxylase (ACC), CCAAT/enhancer-binding protein alpha (C/EBPα), and lipoprotein lipase (LPL). On the other hand, XOS enhanced the mRNA expression levels of zonula occludens-1 (ZO-1), occludin, and claudin-1 in the small intestine; increased the strength of the intestinal barrier; and optimized the composition of the intestinal microbiota. Therefore, it was concluded that XOS regulated the intestinal barrier, changed the intestinal microecology, and played an important role in preventing hyperlipidemia through the unique anatomical advantages of the gut-liver axis.

Sequence- and structure-guided improvement of the catalytic performance of a GH11 family xylanase from Bacillus subtilis

Xylanases produce xylooligosaccharides from xylan and have thus attracted increasing attention for their usefulness in industrial applications. Previously, we demonstrated that the GH11 xylanase XynLC9 from Bacillus subtilis formed xylobiose and xylotriose as the major products with negligible production of xylose when digesting corncob-extracted xylan. Here, we aimed to improve the catalytic performance of XynLC9 via protein engineering. Based on the sequence and structural comparisons of XynLC9 with the xylanases Xyn2 from Trichoderma reesei and Xyn11A from Thermobifida fusca, we identified the N-terminal residues 5-YWQN-8 in XynLC9 as engineering hotspots and subjected this sequence to site saturation and iterative mutagenesis. The mutants W6F/Q7H and N8Y possessed a 2.6- and 1.8-fold higher catalytic activity than XynLC9, respectively, and both mutants were also more thermostable. Kinetic measurements suggested that W6F/Q7H and N8Y had lower substrate affinity, but a higher turnover rate (k_cat), which resulted in increased catalytic efficiency than WT XynLC9. Furthermore, the W6F/Q7H mutant displayed a 160% increase in the yield of xylooligosaccharides from corncob-extracted xylan. Molecular dynamics simulations revealed that the W6F/Q7H and N8Y mutations led to an enlarged volume and surface area of the active site cleft, which provided more space for substrate entry and product release and thus accelerated the catalytic activity of the enzyme. The molecular evolution approach adopted in this study provides the design of a library of sequences that captures functional diversity in a limited number of protein variants.

Effects of the Mixture of Xylooligosaccharides and Egg White Protein on the Physicochemical Properties, Conformation, and Gel-Forming Ability of Culter alburnus Myofibrillar Protein during Multiple Freeze-Thaw Cycles

This study focuses on the effect of the mixture (XO/EW) of xylooligosaccharides (XO) and egg white protein (EW) on the physicochemical properties, conformation, and gel-forming ability of Culter alburnus myofibrillar proteins (MP) during multiple freeze–thaw (FT) cycles. In our methodology, MP samples added with EW, XO, or XO/EW mixture (1%, v/v) are prepared, and after multiple FT cycles, the XO or XO/EW-treated samples show significant (p < 0.05) inhibition on the decrease of sulfhydryl content and the increase of carbonyl content of MP. Compared with EW, XO or XO/EW could delay the increase of surface hydrophobicity and the decline of secondary and tertiary structural properties of MP, indicating that XO or XO/EW could more effectively increase the stability of MP conformation. Meanwhile, XO/EW could more effectively reduce the decrease of gel strength and gel water holding capacity, and the increase in the T₂ relaxation time of MP gel, confirming that XO/EW could substantially improve the MP gel-forming ability. Analysis of intermolecular interaction force proves that, compared with EW, XO/EW could reduce the content decrease of ionic and hydrogen bonds in MP gel. Overall, XO/EW could improve the stability of MP functional properties over multiple FT cycles. This study provides a new perspective for the potential commercial application of EW as a low-calorie cryoprotectant in aquatic products.

A Rapid and Mild Sulfation Strategy Reveals Conformational Preferences in Therapeutically Relevant Sulfated Xylooligosaccharides

Although sulfated xylooligosaccharides are promising therapeutic leads for a multitude of afflictions, the structural complexity and heterogeneity of commercially deployed forms (e. g. Pentosan polysulfate 1) complicates their path to further clinical development. We describe herein the synthesis of the largest homogeneous persulfated xylooligomers prepared to date, comprising up to eight xylose residues, as standards for biological studies. Near quantitative sulfation was accomplished using a remarkably mild and operationally simple protocol which avoids the need for high temperatures and a large excess of the sulfating reagent. Moreover, the sulfated xylooligomer standards so obtained enabled definitive identification of a pyridinium contaminant in a sample of a commercially prepared Pentosan drug and provided significant insights into the conformational preferences of the constituent persulfated monosaccharide residues. As the spatial distribution of sulfates is a key determinant of the binding of sulfated oligosaccharides to endogenous targets, these findings have broad implications for the advancement of Pentosan-based treatments.

Potential Valorization of Hazelnut Shells through Extraction, Purification and Structural Characterization of Prebiotic Compounds: A Critical Review

Hazelnuts are one of the most widely consumed nuts, but their production creates large quantities of by-products, especially shells, that could be upcycled into much more valuable products. Recent studies have shown that hazelnut shell hemicellulose is particularly rich in compounds that are potential precursors of xylooligosaccharides and arabino-xylooligosaccharides ((A)XOS), previously defined as emerging prebiotics very beneficial for human health. The production of these compounds on an industrial scale-up could have big consequences on the functional foods market. However, to produce (A)XOS from a lignocellulosic biomass, such as hazelnut shell, is not easy. Many methods for the extraction and the purification of these prebiotics have been developed, but they all have different efficiencies and consequences, including on the chemical structure of the obtained (A)XOS. The latter, in turn, is strongly correlated to the nutritional effects they have on health, which is why the optimization of the structural characterization process is also necessary. Therefore, this review aims to summarize the progress made by research in this field, so as to contribute to the exploitation of hazelnut waste streams through a circular economy approach, increasing the value of this biomass through the production of new functional ingredients.

Selective Production of Xylooligosaccharides by Xylan Hydrolysis Using a Novel Recyclable and Separable Furoic Acid

Xylooligosaccharides (XOS) have gained considerable attention worldwide as prebiotics due to their immune-strengthening activity and beneficial gut bacteria development and can be produced from xylan-rich resources by acid hydrolysis. The present study proved the organic acid hydrolysis to be beneficial for XOS yield. In this study, a recyclable and separable organic acid, i.e., furoic acid, was used for hydrolyzing xylan to produce XOS, and the response surface methodology design was applied to maximize the XOS yield; the results indicated that the quadratic model terms of the interaction between reaction temperature and hydrolysis time showed the most significant impact on XOS yields (P < 0.05). The predicted maximum yield of XOS was 49.0% with 1.2% furoic acid at 167°C for 33 min, being close to the experimental value (49.2%), indicating that the fitted models were in good agreement with the experimental results. Meanwhile, the primary byproducts, including xylose and furfural, were concurrently bio-oxidized into xylonic acid and furoic acid by Gluconobacter oxydans and separated by electrodialysis. Subsequently, the furoic acid with low solubility (<3.7%, 25°C) was recovered by natural crystallization. The above results indicate that the use of multi-steps contributes to sustainable XOS production by furoic acid.

Xylooligosaccharides Increase Bifidobacteria and Lachnospiraceae in Mice on a High-Fat Diet, with a Concomitant Increase in Short-Chain Fatty Acids, Especially Butyric Acid

Effects of xylooligosaccharides (XOSs) as well as a mixture of XOS, inulin, oligofructose, and partially hydrolyzed guar gum (MIX) in mice fed a high-fat diet (HFD) were studied. Control groups were fed an HFD or a low-fat diet. Special attention was paid to the cecal composition of the gut microbiota and formation of short-chain fatty acids, but metabolic parameters were also documented. The XOS group had significantly higher cecum levels of acetic, propionic, and butyric acids than the HFD group, and the butyric acid content was higher in the XOS than in the MIX group. The cecum microbiota of the XOS group contained more Bifidobacteria, Lachnospiraceae, and S24-7 bacteria than the HFD group. A tendency of lower body weight gain was observed on comparing the XOS and HFD groups. In conclusion, the XOS was shown to be a promising prebiotic candidate. The fiber diversity in the MIX diet did not provide any advantages compared to the XOS diet.

Antioxidant Vitamins and Prebiotic FOS and XOS Differentially Shift Microbiota Composition and Function and Improve Intestinal Epithelial Barrier In Vitro

Human gut microbiota (HGM) play a significant role in health and disease. Dietary components, including fiber, fat, proteins and micronutrients, can modulate HGM. Much research has been performed on conventional prebiotics such as fructooligosaccharides (FOS) and galactooligosaccharides (GOS), however, novel prebiotics or micronutrients still require further validation. We assessed the effect of FOS, xylooligosaccharides (XOS) and a mixture of an antioxidant vitamin blend (AOB) on gut microbiota composition and activity, and intestinal barrier in vitro. We used batch fermentations and tested the short-term effect of different products on microbial activity in six donors. Next, fecal inocula from two donors were used to inoculate the simulator of the human microbial ecosystem (SHIME) and after long-term exposure of FOS, XOS and AOB, microbial activity (short- and branched-chain fatty acids and lactate) and HGM composition were evaluated. Finally, in vitro assessment of intestinal barrier was performed in a Transwell setup of differentiated Caco-2 and HT29-MTX-E12 cells exposed to fermentation supernatants. Despite some donor-dependent differences, all three tested products showed beneficial modulatory effects on microbial activity represented by an increase in lactate and SCFA levels (acetate, butyrate and to a lesser extent also propionate), while decreasing proteolytic markers. Bifidogenic effect of XOS was consistent, while AOB supplementation appears to exert a specific impact on reducing F. nucleatum and increasing butyrate-producing B. wexlerae. Functional and compositional microbial changes were translated to an in vitro host response by increases of the intestinal barrier integrity by all the products and a decrease of the redox potential by AOB supplementation.

Friend or Foe? Impacts of Dietary Xylans, Xylooligosaccharides, and Xylanases on Intestinal Health and Growth Performance of Monogastric Animals

This paper discusses the structural difference and role of xylan, procedures involved in the production of xylooligosaccharides (XOS), and their implementation into animal feeds. Xylan is non-starch polysaccharides that share a β-(1-4)-linked xylopyranose backbone as a common feature. Due to the myriad of residues that can be substituted on the polymers within the xylan family, more anti-nutritional factors are associated with certain types of xylan than others. XOS are sugar oligomers extracted from xylan-containing lignocellulosic materials, such as crop residues, wood, and herbaceous biomass, that possess prebiotic effects. XOS can also be produced in the intestine of monogastric animals to some extent when exogenous enzymes, such as xylanase, are added to the feed. Xylanase supplementation is a common practice within both swine and poultry production to reduce intestinal viscosity and improve digestive utilization of nutrients. The efficacy of xylanase supplementation varies widely due a number of factors, one of which being the presence of xylanase inhibitors present in common feedstuffs. The use of prebiotics in animal feeding is gaining popularity as producers look to accelerate growth rate, enhance intestinal health, and improve other production parameters in an attempt to provide a safe and sustainable food product. Available research on the impact of xylan, XOS, as well as xylanase on the growth and health of swine and poultry, is also summarized. The response to xylanase supplementation in swine and poultry feeds is highly variable and whether the benefits are a result of nutrient release from NSP, reduction in digesta viscosity, production of short chain xylooligosaccharides or a combination of these is still in question. XOS supplementation seems to benefit both swine and poultry at various stages of production, as well as varying levels of XOS purity and degree of polymerization; however, further research is needed to elucidate the ideal dosage, purity, and degree of polymerization needed to confer benefits on intestinal health and performance in each respective species.

AR03: characterization of enzymatic cocktails active on complex carbohydrates for xylooligosaccharides production

Bacillus sp. AR03 have been described as an important producer of carbohydrate-active enzymes (CAZymes) when growing in a peptone-based medium supplemented with simple sugars and/or carboxymethyl cellulose (CMC) as carbon sources. This work aimed to identify the extracellular enzymatic cocktails through shotgun proteomics. The proteomic analysis showed that enzymes involved in cellulose and xylan degradation were among the most abundant proteins. These enzymes included an endo-glucanase GH5_2 and a glucuronoxylanase GH30_8, which were found in all conditions. In addition, several proteins were differentially expressed in the three evaluated culture media, indicating microbial metabolic changes due to the different supplied carbon sources, particularly, in the presence of CMC. Finally, the capability of the crude enzymatic cocktails from culture media to degrade birchwood xylan was assessed, which produced mostly xylooligosaccharides containing among 3-5 xylose units. Consequently, this work shows the potential of the extracellular enzymes from Bacillus sp. AR03 for producing emergent prebiotics.

Effect of Oligosaccharide Degree of Polymerization on the Induction of Xylan-Degrading Enzymes by Fusarium oxysporum f. sp. Lycopersici

Xylan is one of the most abundant carbohydrates on Earth. Complete degradation of xylan is achieved by the collaborative action of endo-β-1,4-xylanases and β-d-xylosidases and a number of accessories enzymes. In filamentous fungi, the xylanolytic system is controlled through induction and repression. However, the exact mechanism remains unclear. Substrates containing xylan promote the induction of xylanases, which release xylooligosaccharides. These, in turn, induce expression of xylanase-encoding genes. Here, we aimed to determine which xylan degradation products acted as inducers, and whether the size of the released oligomer correlated with its induction strength. To this end, we compared xylanase production by different inducers, such as sophorose, lactose, cellooligosaccharides, and xylooligosaccharides in Fusarium oxysporum f. sp. lycopersici. Results indicate that xylooligosaccharides are more effective than other substrates at inducing endoxylanase and β-xylosidases. Moreover, we report a correlation between the degree of xylooligosaccharide polymerization and induction efficiency of each enzyme. Specifically, xylotetraose is the best inducer of endoxylanase, xylohexaose of extracellular β-xylosidase, and xylobiose of cell-bound β-xylosidase.

Prebiotics Regulation of Intestinal Microbiota Attenuates Cognitive Dysfunction Induced by Surgery Stimulation in APP/PS1 Mice

Emerging evidence indicates that the intestinal microbiota could interact with the central nervous system and modulate multiple pathophysiological changes, including the integrity of intestinal barrier and blood-brain barrier, as well as neuroinflammatory response. In the present study, we investigated the potential role of intestinal microbiota in the pathophysiological process of postoperative cognitive dysfunction. Six-month-old APP/PS1 mice were subjected to partial hepatectomy to establish surgery model and exhibited cognitive dysfunction. The expressions of inflammatory mediators increased and tight junction proteins (ZO-1 and Occludin) levels decreased in the intestine and hippocampus. The 16S ribosomal RNA gene sequencing showed altered β diversity and intestinal microbiota richness after surgery, including genus Rodentibacter, Bacteroides, Ruminococcaceae_UCG_014 and Faecalibaculum, as well as family Eggerthellaceae and Muribaculaceae. Furthermore, prebiotics (Xylooligosaccharides, XOS) intervention effectively attenuated surgery-induced cognitive dysfunction and intestinal microbiota alteration, reduced inflammatory responses, and improved the integrity of tight junction barrier in the intestine and hippocampus. In summary, the present study indicates that intestinal microbiota alteration, the related intestinal barrier and blood-brain barrier damage, and inflammatory responses participate the pathophysiological process of postoperative cognitive dysfunction. Prebiotics intervention could be a potential preventative approach.

Biochemical Characterization of Xylanases from Streptomyces sp. B6 and Their Application in the Xylooligosaccharide Production from Viscose Fiber Production Waste

Enzymatic hydrolysis of xylan represents a promising way to produce xylooligosaccharide (XOS), which is a novel ingredient in functional food. However, the recalcitrance of xylan in natural lignocellulosic biomass entails effective and robust xylanases. In the present study, we reported the isolation of a thermophilic Streptomyces sp. B6 from mushroom compost producing high xylanase activity. Two xylanases of Streptomyces sp. B6 belonging to GH10 (XynST10) and GH11 (XynST11) families were thus identified and biochemically characterized to be robust enzymes with high alkaline- and thermostability. Direct hydrolysis of neutralized viscose fiber production waste using XynST10 and XynST11 showed that while XynST10 produced 23.22 g/L XOS with a degree of polymerization (DP) of 2-4 and 9.27 g/L xylose, XynST11 produced much less xylose (1.19 g/L) and a higher amounts of XOS with a DP = 2-4 (28.29 g/L). Thus, XynST11 holds great potential for the production of XOS from agricultural and industrial waste.

Secondary Lactic Acid Bacteria Fermentation with Wood-Derived Xylooligosaccharides as a Tool To Expedite Sour Beer Production

Xylooligosaccharides (XOS) from woody biomass were evaluated as a substrate for secondary lactic acid bacteria (LAB) fermentation in sour beer production. XOS were extracted from birch (Betula pubescens) and added to beer to promote the growth of Lactobacillus brevis BSO 464. Growth, pH, XOS degradation, and metabolic products were monitored throughout fermentations, and the final beer was evaluated sensorically. XOS were utilized, metabolic compounds were produced (1800 mg/L lactic acid), and pH was reduced from 4.1 to 3.6. Secondary fermentation changed sensory properties significantly, and the resulting sour beer was assessed as similar to a commercial reference in multiple attributes, including acidic taste. Overall, secondary LAB fermentation induced by wood-derived XOS provided a new approach to successfully produce sour beer with reduced fermentation time (from 1-3 years to 4 weeks). The presented results demonstrate how hemicellulosic biomass can be valorized for beverage production and to obtain sour beer with improved process control.

Antihyperglycemic effect of rice husk derived xylooligosaccharides in high-fat diet and low-dose streptozotocin-induced type 2 diabetic rat model

Rice husk (RH) is an agricultural waste obtained from rice milling process. Our previous study demonstrated the optimized process of extracting xylooligosaccharides (XOS), a prebiotic that can support the growth and activity of beneficial gut microbiota, from RH. Accumulated evidences indicate that the composition of gut microbiota is involved in the progression of insulin resistance and diabetes. This study aims to evaluate the antihyperglycemic effect and putative mechanisms of RH-XOS using a diabetic rat model induced by high-fat diet and streptozotocin injection. Diabetic rats were randomly assigned to receive vehicle (DMC), XOS (DM-XOS), metformin (DMM), and a combination of XOS and metformin (DMM-XOS). An additional group of rats were fed with normal diet plus vehicle (NDC) and normal diet plus XOS (ND-XOS). Supplementation with RH-XOS for 12 weeks successfully decreased the fasting plasma glucose, insulin, leptin, and LPS levels in DM-XOS compared with DMC. Likewise, the insulin-stimulated glucose uptake assessed by in vitro study was significantly enhanced in DM-XOS, DMM, and DMM-XOS. The diminished protein expressions of GLUT4 and pAktSer473 as well as pAMPKThr172 were significantly modulated in DM-XOS, DMM, and DMM-XOS groups. Interestingly, RH-XOS supplementation reversed the changed gut permeability, elevated the number of beneficial bacteria, both Lactobacillus and Bifidobacterium spp., and increased SCFAs production. Taken together, the results confirm the efficacy of RH-XOS in achieving good glycemic control in diabetes by maintenance of gut microbiota and attenuation of endotoxemia. The findings reveal the benefits of RH-XOS and open an opportunity to improve its value by its development as a nutraceutical for diabetes.

Laboratory Evolution of GH11 Endoxylanase Through DNA Shuffling: Effects of Distal Residue Substitution on Catalytic Activity and Active Site Architecture

Endoxylanase with high specific activity, thermostability, and broad pH adaptability is in huge demand. The mutant library of GH11 endoxylanase was constructed via DNA shuffling by using the catalytic domain of Bacillus amyloliquefaciens xylanase A (BaxA) and Thermomonospora fusca TF xylanase A (TfxA) as parents. A total of 2,250 colonies were collected and 756 of them were sequenced. Three novel mutants (DS153: N29S, DS241: S31R and DS428: I51V) were identified and characterized in detail. For these mutants, three residues of BaxA were substituted by the corresponding one of TfxA_CD. The specific activity of DS153, DS241, and DS428 in the optimal condition was 4.54, 4.35, and 3.9 times compared with the recombinant BaxA (reBaxA), respectively. The optimum temperature of the three mutants was 50°C. The optimum pH for DS153, DS241, and DS428 was 6.0, 7.0, and 6.0, respectively. The catalytic efficiency of DS153, DS241, and DS428 enhanced as well, while their sensitivity to recombinant rice xylanase inhibitor (RIXI) was lower than that of reBaxA. Three mutants have identical hydrolytic function as reBaxA, which released xylobiose–xylopentaose from oat spelt, birchwood, and beechwood xylan. Furthermore, molecular dynamics simulations were performed on BaxA and three mutants to explore the precise impact of gain-of-function on xylanase activity. The tertiary structure of BaxA was not altered under the substitution of distal residues (N29S, S31R, and I51V); it induced slightly changes in active site architecture. The distal impact rescued the BaxA from native conformation (“closed state”) through weakening interactions between “gate” residues (R112, N35 in DS241 and DS428; W9, P116 in DS153) and active site residues (E78, E172, Y69, and Y80), favoring conformations with an “open state” and providing improved activity. The current findings would provide a better and more in-depth understanding of how distal single residue substitution improved the catalytic activity of xylanase at the atomic level.

Oligosaccharides Preparation from Rice Bran Arabinoxylan by Two Different Commercial Endoxylanase Enzymes

Xylooligosaccharides (XOS) and arabinoxylooligosaccharides (AXOS), potential prebiotics, can be produced from rice bran arabinoxylan (RBAX) using commercial endoxylanase enzymes. However, differences in rice bran cultivars and endoxylanase enzyme types may affect extracted oligosaccharides (OS) yields. This study investigated extracted OS structures derived from three different RBAX using two commercial endoxylanase enzymes. RBAX extracted from commercially defatted rice bran (CDRB) yielded the greatest OS amount (456.69 mg/g RBAX), followed by that of the San-Pah-Tawng1 (SPT1) cultivar (231.7 mg/g RBAX), and lastly, the Chai-Nat1 (CN1) cultivar (172.57 mg/g RBAX), as evidenced via Ultraflo L enzyme hydrolysis. Ultraflo Max enzyme hydrolysis produced a similar trend, however, OS amounts from all RBAX sources were remarkably lower (83.39 mg/g RBAX extracted from CDRB, 27.05 mg/g RBAX from SPT1 cultivar, and 21.53 mg/g RBAX from CN1 cultivar). Interestingly, 3²-α-L-Araf-(1-4)-β-D-xylobiose (A³X) was the primary AXOS product in all RBAX hydrolysates prepared by Ultraflo Max. RBAX extracted from CDRB solubilized by Ultraflo L (45.67% weight of RBAX) had higher OS yields than that obtained via Ultraflo Max (8.3% weight of RBAX). Ultraflo L was therefore a suitable commercial enzyme for short-chain OS conversion from RBAX.

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.

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.

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.

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

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

Utility of Thermostable Xylanases of Mycothermus thermophilus in Generating Prebiotic Xylooligosaccharides

Xylooligosaccharides as emerging prebiotics are able to promote the growth of probiotic bacteria. In the present study, four neutral, thermostable xylanases (MtXyn11A, MtXyn11At, MtXyn11B, and MtXyn11C) from compost fungus Mycothermus thermophilus CGMCC3.18119 were overexpressed in Pichia pastoris GS115 and used to produce xylooligosaccharides from beechwood xylan. The enzymes showed similar enzymatic properties (maximal activities at pH 6.0-6.5 and 65 °C) but varied in catalytic efficiency and cleaving actions. MtXyn11A, MtXyn11At, and MtXyn11C mainly produced xylobiose (59-62%), xylose (16-20%), and xylotriose (16-19%), while MtXyn11B released xylobiose (51%), xylotriose (32%), and xylose (12%) as the main products. When using the xylan hydrolysates of different xylanases as the carbon source, four probiotic Lactobacillus strains Lactobacillus brevis 1.2028, Lactobacillus rhamnosus GG, Lactobacillus casei BL23, and Lactobacillus plantarum WCSF1 were confirmed to use the xylooligosaccharides efficiently (83.8-98.2%), with L. brevis 1.2028 as the greatest.

Mannan- and xylooligosaccharides modulate caecal microbiota and expression of inflammatory-related cytokines and reduce caecal Salmonella Enteritidis colonisation in young chickens

Salmonella Enteritidis is a pathogen, which can infect humans and chickens. This study was designed to address the impact of two potential prebiotics, mannanoligosaccharides (MOS) and xylooligosaccharides (XOS), on the caecal microbiota and expression of cytokines in chickens infected with S. Enteritidis. Newly hatched chicks were assigned to one of five groups: (1) uninfected control, (2) infected control, (3) infected + XOS, (4) infected + MOS and (5) infected + virginiamycin. The number of S. Enteritidis recovered from the caecum was significantly lower, by 1.6 log, in the MOS, and to a less extent (1.0 log) in the XOS-fed birds compared to the infected control. Coprococcus, Ruminococcus and Enterococcus genera were increased in response to MOS, whereas XOS enriched Clostridium, Lactobacillus and Roseburia MOS, but not XOS, lessened the increase of lipopolysaccharide-induced tumour necrosis factor alpha factor and interferon-γ in caecal tonsils after challenge. The canonical correspondence analysis for cytokine genes showed a correlation with the composition of the microbial community at the genus level. Thus, MOS and XOS differently changed the relative abundance of specific microbial genera and the immune response during infection, and these changes were correlated with their abilities to reduce S. Enteritidis colonisation.

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

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

Screening of Xylanolytic Aspergillus fumigatus for Prebiotic Xylooligosaccharide Production Using Bagasse

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

Gene expression of enzymes involved in utilization of xylooligosaccharides by Lactobacillus strains

Prebiotics are defined as food components that confer health benefits on the host through modulation of the microbiota. Xylooligosaccharides (XOS) are non-digestible oligosaccharides that have recently received increasing attention as potential prebiotic candidates. XOS are sugar oligomers composed of 1,4-linked xylopyranosyl backbone and are obtained by either chemical or, more commonly, enzymatic hydrolysis of xylan polysaccharides, extracted from the plant cell wall. The bifidogenic effect of XOS was demonstrated by both in vitro studies and small-scale in vivo human studies. Some intestinal bacterial strains are able to grow on XOS, yet numerous studies have demonstrated that the ability to utilize these oligosaccharides varies considerably among these bacteria. The aim of this study is to investigate the ability of several strains Lactobacillus to use XOS. Fifteen Lactobacillus strains, allifiated to L. plantarum, L. brevis and L. sakei, were studied. Screening procedure was performed for the ability of the strains to utilize XOS as an alternative carbon source. Only some of them utilize XOS. The growth kinetics show the presence of two lag phases, indicating that these bacteria utilize probably some monosaccharides present in the used XOS. XOS were fermented with high specificity by Bifidobacteria strains, but Lactobacilli did not metabolize XOS efficiently.

Trichoderma reesei XYN VI--a novel appendage-dependent eukaryotic glucuronoxylan hydrolase

Expression of a Trichoderma reesei gene coding for a putative GH30 xylanase in Aspergillus oryzae led to isolation and purification of a novel xylanase exhibiting catalytic properties different from those of the previously characterized GH30 xylanase XYN IV of T. reesei. The novel enzyme, named XYN VI, exhibited catalytic properties similar to appendage-dependent GH30 glucuronoxylanases previously recognized only in bacteria. XYN VI showed high specific activity only on xylans or xylooligosaccharides containing 4-O-methyl-D-glucuronic acid or D-glucuronic acid side substituents. The cleavage of the main chain takes place primarily at the second glycosidic linkage from the branch towards the reducing end of the polysaccharides or aldouronic acids. These catalytic properties resemble bacterial GH30 glucuronoxylanases, although the recognition of the uronic acid side chains by XYN VI is apparently based on interaction of the substrate with other amino acids. Moreover, in contrast to bacterial enzymes, XYN VI is also capable of slower but significant cleavage of unsubstituted parts of xylan and acidic xylooligosaccharides. The data point to a great catalytic diversity of xylanases produced by the most extensively studied cellulolytic fungus.

Determinants for the improved thermostability of a mesophilic family 11 xylanase predicted by computational methods

BACKGROUND

Xylanases have drawn much attention owing to possessing great potential in various industrial applications. However, the applicability of xylanases, exemplified by the production of bioethanol and xylooligosaccharides (XOSs), was bottlenecked by their low stabilities at higher temperatures. The main purpose of this work was to improve the thermostability of AuXyn11A, a mesophilic glycoside hydrolase (GH) family 11 xylanase from Aspergillus usamii E001, by N-terminus replacement.

RESULTS

A hybrid xylanase with high thermostability, named AEXynM, was predicted by computational methods, and constructed by substituting the N-terminal 33 amino acids of AuXyn11A with the corresponding 38 ones of EvXyn11TS, a hyperthermostable family 11 xylanase. Two AuXyn11A- and AEXynM-encoding genes, Auxyn11A and AExynM, were then highly expressed in Pichia pastoris GS115, respectively. The specific activities of two recombinant xylanases (reAuXyn11A and reAEXynM) were 10,437 and 9,529 U mg-1. The temperature optimum and stability of reAEXynM reached 70 and 75°C, respectively, much higher than those (50 and 45°C) of reAuXyn11A. The melting temperature (Tm) of reAEXynM, measured using the Protein Thermal Shift (PTS) method, increased by 34.0°C as compared with that of reAuXyn11A. Analyzed by HPLC, xylobiose and xylotriose as the major hydrolytic products were excised from corncob xylan by reAEXynM. Additionally, three single mutant genes from AExynM (AExynMC5T, AExynMP9S, and AExynMH14N) were constructed by site-directed mutagenesis as designed theoretically, and expressed in P. pastoris GS115, respectively. The thermostabilities of three recombinant mutants clearly decreased as compared with that of reAEXynM, which demonstrated that the three amino acids (Cys5, Pro9, and His14) in the replaced N-terminus contributed mainly to the high thermostability of AEXynM.

CONCLUSIONS

This work highly enhanced the thermostability of AuXyn11A by N-terminus replacement, and further verified, by site-directed mutagenesis, that Cys5, Pro9, and His14 contributed mainly to the improved thermostability. It will provide an effective strategy for improving the thermostabilities of other enzymes.

Strong cellulase inhibitors from the hydrothermal pretreatment of wheat straw

BACKGROUND

The use of the enzymatic hydrolysis of lignocellulose with subsequent fermentation to ethanol provides a green alternative for the production of transportation fuels. Because of its recalcitrant nature, the lignocellulosic biomass must be pretreated before enzymatic hydrolysis. However, the pretreatment often results in the formation of compounds that are inhibitory for the enzymes or fermenting organism. Although well recognized, little quantitative information on the inhibition of individual cellulase components by identified inhibitors is available.

RESULTS

Strong cellulase inhibitors were separated from the liquid fraction of the hydrothermal pretreatment of wheat straw. HPLC and mass-spectroscopy analyses confirmed that the inhibitors were oligosaccharides (inhibitory oligosaccharides, IOS) with a degree of polymerization from 7 to 16. The IOS are composed of a mixture of xylo- (XOS) and gluco-oligosaccharides (GOS). We propose that XOS and GOS are the fragments of the xylan backbone and mixed-linkage β-glucans, respectively. The IOS were approximately 100 times stronger inhibitors for Trichoderma reesei cellobiohydrolases (CBHs) than cellobiose, which is one of the strongest inhibitors of these enzymes reported to date. Inhibition of endoglucanases (EGs) by IOS was weaker than that of CBHs. Most of the tested cellulases and hemicellulases were able to slowly degrade IOS and reduce the inhibitory power of the liquid fraction to some extent. The most efficient single enzyme component here was T. reesei EG TrCel7B. Although reduced by the enzyme treatment, the residual inhibitory power of IOS and the liquid fraction was strong enough to silence the major component of the T. reesei cellulase system, CBH TrCel7A.

CONCLUSIONS

The cellulase inhibitors described here may be responsible for the poor yields from the enzymatic conversion of the whole slurries from lignocellulose pretreatment under conditions that do not favor complete degradation of hemicellulose. Identification of the inhibitory compounds helps to design better enzyme mixtures for their degradation and to optimize the pretreatment regimes to minimize their formation.

Evidence for xylooligosaccharide utilization in Weissella strains isolated from Indian fermented foods and vegetables

Six strains isolated from fermented food were identified as Weissella species by 16S rDNA sequencing, clustering with the species pair W. confusa/W. cibaria. The strains were analysed for growth on glucose, xylose and xylooligosaccharides (XOS). All strains were xylose positive using the API CHL 50 test. Growth on XOS was observed for strains 85, 92, 145 and AV1, firstly by optical density measurements in microtitre plates and secondly in batch cultures also confirming concomitant decrease in pH. Analysis of XOS before and after growth established consumption in the DP2-DP5 range in the four XOS-fermenting strains. XOS were consumed simultaneously with glucose, while xylose was consumed after glucose depletion. Cell-associated β-xylosidase activity was detected in the XOS-fermenting strains. Analysis of genomic data suggests this activity to be linked with genes encoding glycoside hydrolases from family 3, 8 or 43. No endo-β-xylanase activity was detectable. Major end products were lactate and acetate. A higher ratio of acetic acid to lactic acid was obtained during growth on XOS compared with growth on glucose. This is the first report on utilization of XOS in Weissella, indicating an increased probiotic potential for XOS-utilizing strains from the species pair W. confusa/W. cibaria, but also showing that XOS utilization is strain dependent for these species.