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.

Proteomic analysis of secretomes from Bacillus sp. 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.