Metabolic Profiling of Xylooligosaccharides by Lactobacilli

Heterologous expression and characterization of xylose-tolerant GH 43 family β-xylosidase/α-L-arabinofuranosidase from Limosilactobacillus fermentum and its application in xylan degradation

The degradation of hemicellulose, including xylan, is an important industrial process as it provides cheap and sustainable source of economically valuable monosaccharides. β-xylosidases are key enzymes required for complete degradation of xylan and are used in the production of monosaccharides, such as xylose. In this study, we characterized a novel, xylose-tolerant β-xylosidase isolated from Limosilactobacillus fermentum SK152. Sequence analysis and protein structure prediction revealed that the putative β-xylosidase belongs to the glycoside hydrolase (GH) family 43 subfamily 11 and exhibits high homology with other characterised GH43 β-xylosidases from fungal and bacterial sources. The putative β-xylosidase was named LfXyl43. The catalytic residues of LfXyl43, which are highly conserved among GH 43 β-xylosidases, were predicted. To fully characterise LfXyl43, the gene encoding it was heterologously expressed in Escherichia coli. Biochemical characterisation revealed that the recombinant LfXyl43 (rLfXyl43) was active against artificial and natural substrates containing β-1,4-xylanopyranosyl residues, such as p-nitrophenyl-β-D-xylopyranoside (pNPX) and oNPX. Moreover, it demonstrated weak α-L-arabinofuranosidase activity. The optimal activity of rLfXyl43 was obtained at pH 7.0 at 35°C. rLfXyl43 could degrade xylo-oligosaccharides, such as xylobiose, xylotriose, and xylotetraose, and showed hydrolysing activity towards beechwood xylan. Moreover, rLfXyl43 demonstrated synergy with a commercial xylanase in degrading rye and wheat arabinoxylan. The activity of rLfXyl43 was not affected by the addition of metal ions, chemical reagents, or high concentrations of NaCl. Notably, rLfXyl43 exhibited tolerance to high xylose concentrations, with a K i value of 100.1, comparable to that of other xylose-tolerant GH 43 β-xylosidases. To our knowledge, this is the first β-xylosidase identified from a lactic acid bacterium with high tolerance to salt and xylose. Overall, rLfXyl43 exhibits great potential as a novel β-xylosidase for use in the degradation of lignocellulosic material, especially xylan hemicellulose. Its high activity against xylo-oligosaccharides, mild catalytic conditions, and tolerance to high xylose concentrations makes it a suitable enzyme for industrial applications.

Phenotypic and genomic characterization of Levilactobacillus brevis YT108: a potential probiotic strain capable of metabolizing xylo-oligosaccharides

Levilactobacillus brevis YT108, identified for its ability to metabolize prebiotic xylo-oligosaccharides (XOS), emerges as a candidate for probiotic use in synbiotic food formulations. This study aimed to investigate the metabolic and genomic traits associated with XOS metabolism in YT108 and to assess its probiotic attributes through whole genome sequencing and in vitro assays. Strain YT108 exhibited robust growth kinetics on XOS as the sole carbon source, with a growth profile comparable to that on glucose, achieving a pH reduction to 4.68 and an OD600nm of 1.603 after 48 h. Three key gene clusters (xylCDEPFRT, xylHTG, and xylABT) and key enzymes (1,4-β-xylosidase) were identified as potentially involved in XOS metabolism. In vitro assays confirmed the strain's remarkable physiological properties, including tolerance to acid, bile, heat, and NaCl, as well as resistance to simulated gastrointestinal juices and antioxidant capacity. Furthermore, strain YT108 was sensitive to five commonly used antibiotics and lacked transferable resistance genes. Taken together, these results highlight the potential of L. brevis YT108 as a probiotic candidate with beneficial traits for XOS utilization, suggesting its promising application in the formulation of next-generation synbiotic products.

Nutrients, Phytochemicals, and Antioxidant Capacity of Red Raspberry Nectar Fermented with Lacticaseibacillus paracasei

Fresh raspberries are highly perishable, but lactic acid bacteria fermentation offers a favourable method for developing healthy products. This study investigated the effects of Lacticaseibacillus paracasei fermentation on the nutrients and phytochemicals of red raspberry nectar using widely targeted metabolomics, as well as its antioxidant activity. The fermentation notably disrupted the raspberry tissue structure, reshaped its non-volatile composition, and increased its DPPH and hydroxyl free radical scavenging abilities. A total of 261 compounds showed significant differences, with 198 upregulated and 63 downregulated. Among these, certain flavonoid glucosides (e.g., pelargonid-in-3-O-rutinoside, delphinidin-3-O-rutinoside-7-O-glucoside, and kaempferol-3-O-glucoside) were significantly downregulated, while some bioactive phenolic acids (e.g., 3-(4-Hydroxyphenyl)-propionic acid and DL-3-phenyllactic acid), alkaloids (e.g., deoxymutaaspergillic acid and indole-3-lactic acid), amino acids (e.g., L-phenylalanine and L-glutamine), and B vitamins (e.g., VB6, VB7, and VB3) were substantially upregulated. Furthermore, the Kyoto Encyclopedia of Genes and Genomes (KEGG) annotation and enrichment analysis revealed that metabolic pathways and the biosynthesis of secondary metabolites contributed significantly to the new profile of fermented red raspberry nectar. These findings provide valuable insights for developing fermented raspberry products using Lacticaseibacillus paracasei, which can help minimise fresh raspberry loss and enhance their valorisation.

Valorisation of sawdust-based spent mushroom substrate for sustainable xylooligosaccharides production using low-cost crude xylanases from Aspergillus flavus KUB2

Spent mushroom substrate (SMS), a lignocellulosic waste after mushroom production is generally discarded without proper management. There is increasing interest in the sustainable transformation of lignocellulosic waste into high-value products. Within this context, the present study investigated the potential of the SMS from the cultivation of Pleurotus pulmonarius and Auricularia auricula on rubber tree wood sawdust as substrates for xylooligosaccharides (XOS) production. SMS samples from these two edible mushrooms were extracted using alkaline xylan extraction, producing maximum true recovery amounts of xylan in the range 34.61%-37.49% using 18% NaOH at 70 °C for 3 h. Production of XOS from alkaline-extracted xylan from the SMS samples of both mushroom species using economically crude xylanases from Aspergillus flavus KUB2 resulted in XOS (X2-X5) production of 241.47-249.04 mg/g, with X3 as the predominant XOS product. The produced XOS had excellent prebiotic activity and 2,2'-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activity and contained high total phenolic contents. The combined beneficial bioactivities in terms of prebiotic and antioxidant properties suggested that the XOS produced from sawdust-based SMS samples of P. pulmonarius and A. auricula could be promising ingredients for both food and pharmaceutical applications.

Structure-dependent stimulation of gut bacteria by arabinoxylo-oligosaccharides (AXOS): a review

Arabinoxylo-oligosaccharides (AXOS) are non-digestible dietary fibers that potentially confer a health benefit by stimulating beneficial bacteria in the gut. Still, a detailed overview of the diversity of gut bacteria and their specificity to utilize structurally different AXOS has not been provided to date and was aimed for in this study. Moreover, we assessed the genetic information of summarized bacteria, and we extracted genes expected to encode for enzymes that are involved in AXOS hydrolysis (based on the CAZy database). The taxa involved in AXOS fermentation in the gut display a large variety of AXOS-active enzymes in their genome and consequently utilize AXOS to a highly different extent. Clostridia and Bacteroidales are generalists that consume many structurally diverse AXOS, whereas Bifidobacterium are specialists that specifically consume AXOS with a low degree of polymerization. Further complexity is evident from the fact that the exact bacterial species, and in some cases even the bacterial strains (e.g. in Bifidobacterium longum) that are stimulated, highly depend on the specific AXOS molecular structure. Furthermore, certain species in Bifidobacterium and Lactobacillaceae are active as cross-feeders and consume monosaccharides and unbranched short xylo-oligosaccharides released from AXOS. Our review highlights the possibility that (enzymatic) fine-tuning of specific AXOS structures leads to improved precision in targeting growth of specific beneficial bacterial species and strains in the gut.

Natural antimicrobial oligosaccharides in the food industry

An increase in the number of antibiotic resistance genes burdens the environment and affects human health. Additionally, people have developed a cautious attitude toward chemical preservatives. This attitude has promoted the search for new natural antimicrobial substances. Oligosaccharides from various sources have been studied for their antimicrobial and prebiotic effects. Antimicrobial oligosaccharides have several advantages such as being produced from renewable resources and showing antimicrobial properties similar to those of chemical preservatives. Their excellent broad-spectrum antibacterial properties are primarily because of various synergistic effects, including destruction of pathogen cell wall. Additionally, the adhesion of harmful microorganisms and the role of harmful factors may be reduced by oligosaccharides. Some natural oligosaccharides were also shown to stimulate the growth probiotic organisms. Therefore, antimicrobial oligosaccharides have the potential to meet food processing industry requirements in the future. The latest progress in research on the antimicrobial activity of different oligosaccharides is demonstrated in this review. The possible mechanism of action of these antimicrobial oligosaccharides is summarized with respect to their direct and indirect effects. Finally, the extended applications of oligosaccharides from the food source industry to food processing are discussed.

Application of Endoxylanases of Bacillus halodurans for Producing Xylooligosaccharides from Empty Fruit Bunch

Endo-1,4-β-xylanase catalyzes the random hydrolysis of β-1,4-D-xylosidic bonds in xylan, resulting in the formation of oligomers of xylose. This study aims to demonstrate the promise of endoxylanases from alkaliphilic Bacillus halodurans for the production of xylooligosaccharides (XOS) from oil palm empty fruit bunch (EFB) at high pH. Two enzyme preparations were employed: recombinant endoxylanase Xyn45 (GH10 xylanase) and nonrecombinant endoxylanases, a mixture of two extracellular endo-1,4-β-xylanases Xyn45 and Xyn23 (GH11 xylanase) produced by B. halodurans. EFB was first treated with an alkaline solution. Then, the dissolved xylan-containing fraction was retained, and a prepared enzyme was added to react at pH 8 to convert xylan into XOS. Compared with the use of only Xyn45, the combined use of Xyn45 and Xyn23 resulted in a higher yield of XOS, suggesting the synergistic effect of the two endoxylanases. The yield of XOS obtained from EFB was as high as 46.77% ± 1.64% (w/w), with the xylobiose-to-xylotriose ratio being 6:5. However, when the enzyme activity dose was low, the product contained more xylotriose than xylobiose. Four probiotic lactobacilli and bifidobacteria grew well on a medium containing XOS from EFB. The presence of XOS increased cell mass and reduced pH, suggesting that XOS promoted the growth of probiotics.

The Controlled Semi-Solid Fermentation of Seaweeds as a Strategy for Their Stabilization and New Food Applications

For centuries, macroalgae, or seaweeds, have been a significant part of East Asian diets. In Europe, seaweeds are not considered traditional foods, even though they are increasingly popular in Western diets in human food applications. In this study, a biological processing method based on semi-solid fermentation was optimized for the treatment of the seaweed Gracilaria gracilis. For the first time, selected lactic acid bacteria and non-conventional coagulase-negative staphylococci were used as starter preparations for driving a bio-processing and bio-stabilization of raw macroalga material to obtain new seaweed-based food prototypes for human consumption. Definite food safety and process hygiene criteria were identified and successfully applied. The obtained fermented products did not show any presence of pathogenic or spoilage microorganisms, thereby indicating safety and good shelf life. Lactobacillus acidophilus-treated seaweeds revealed higher α-amylase, protease, lipase, endo-cellulase, and endo-xylanase activity than in the untreated sample. This fermented sample showed a balanced n-6/n-3 fatty acid ratio. SBM-11 (Lactobacillus sakei, Staphylococcus carnosus and Staphylococcus xylosus) and PROMIX 1 (Staphylococcus xylosus) treated samples showed fatty acid compositions that were considered of good nutritional quality and contained relevant amounts of isoprenoids (vitamin E and A). All the starters improved the nutritional value of the seaweeds by significantly reducing the insoluble indigestible fractions. Preliminary data were obtained on the cytocompatibility of G. gracilis fermented products by in vitro tests. This approach served as a valid strategy for the easy bio-stabilization of this valuable but perishable food resource and could boost its employment for newly designed seaweed-based food products.

Natural Xylooligosaccharides Exert Antitumor Activity via Modulation of Cellular Antioxidant State and TLR4

It has been recently proven that xylooligosaccharides (XOS) with prebiotic properties have diverse beneficial biological effects including immunomodulatory and antitumor activities. The present article focused on the chemical and biological evaluation of corn-derived commercially available XOS and aimed to elucidate their cytotoxicity and inhibitory potential against tumor cells. Spectrophotometric chemical analyses, Fourier transform infrared spectroscopy, and high-performance liquid chromatography analyses were performed. Antioxidant activity was determined by measuring the oxygen radical absorbance capacity and hydroxyl radical averting capacity. In vitro cytotoxicity assays with human cell lines derived from normal and tumor tissues, assessments of ATP production, mitochondrial membrane potential specific staining, cytokine assays, and molecular docking were used to evaluate the biological activity of XOS. The sample showed significant antioxidant activity, and it was determined that most xylose oligomers in it are composed of six units. XOS exhibited antitumor activity with pronounced inhibitory effect on lysosomes, but mitochondrial functionality was also affected. The production of proinflammatory cytokines by lipopolysaccharide-stimulated U-937 cells was reduced by XOS treatment, which suggested the involvement of Toll-like receptor 4 (TLR4)-mediated signaling in the mechanism of XOS action. Molecular docking analyses confirmed the potential inhibitory interaction between the sample and TLR4. In addition, XOS treatment had significant tumor-cell-specific influence on the glutathione antioxidant system, affecting its balance and thus contributing to the inhibition of cellular viability. The present study elucidated the tumor-inhibitory potential of commercially available XOS that could be utilized in pharmaceutical and food industry providing disease-preventive and therapeutic benefits.

Cranberry Arabino-Xyloglucan and Pectic Oligosaccharides Induce Lactobacillus Growth and Short-Chain Fatty Acid Production

Numerous health benefits have been reported from the consumption of cranberry-derived products, and recent studies have identified bioactive polysaccharides and oligosaccharides from cranberry pomace. This study aimed to further characterize xyloglucan and pectic oligosaccharide structures from pectinase-treated cranberry pomace and measure the growth and short-chain fatty acid production of 86 Lactobacillus strains using a cranberry oligosaccharide fraction as the carbon source. In addition to arabino-xyloglucan structures, cranberry oligosaccharides included pectic rhamnogalacturonan I which was methyl-esterified, acetylated and contained arabino-galacto-oligosaccharide side chains and a 4,5-unsaturated function at the non-reducing end. When grown on cranberry oligosaccharides, ten Lactobacillus strains reached a final culture density (ΔOD) ≥ 0.50 after 24 h incubation at 32 °C, which was comparable to L. plantarum ATCC BAA 793. All strains produced lactic, acetic, and propionic acids, and all but three strains produced butyric acid. This study demonstrated that the ability to metabolize cranberry oligosaccharides is Lactobacillus strain specific, with some strains having the potential to be probiotics, and for the first time showed these ten strains were capable of growth on this carbon source. The novel cranberry pectic and arabino-xyloglucan oligosaccharide structures reported here combined with the Lactobacillus strains that can metabolize cranberry oligosaccharides and produce short-chain fatty acids, have excellent potential as health-promoting synbiotics.

Functional oligosaccharide fermentation in the gut: Improving intestinal health and its determinant factors-A review

The human intestine is characterized by an abundance of nutrients and a complex microbiota that make crucial contributions to overall health. These nutrients facilitate the adaptation of resident commensals to extreme environments and the development of a robust ecological network in host species. Long-term deprivation of microbiota-accessible carbohydrates (MACs) in the gut results in a loss of bacterial diversity, disruption of intestinal barrier function, and inflammatory diseases. Functional oligosaccharides are excellent MACs possessing important prebiotic properties for intestinal health through their fermentation in the gut. Its mechanism of action is predominantly attributed to acting as carbon sources for specific probiotics, promoting short-chain fatty acids production, and regulating the gut microbiota. In this review, we describe the source and structural characteristics of functional oligosaccharides, provide a framework for strategies to improve intestinal health by oligosaccharide fermentation and discuss structural determinants influencing the functional properties of oligosaccharides.

Isolation of Efficient Xylooligosaccharides-Fermenting Probiotic Lactic Acid Bacteria from Ethnic Pickled Bamboo Shoot Products

Xylooligosaccharides (XOSs) are produced from xylan, which is a component of the hemicellulose that can be found in bamboo shoots. Naw Mai Dong, an ethnic pickled bamboo shoot product of northern Thailand, is generally characterized as acidic and has a sour taste. It can be considered a potential source of probiotic lactic acid bacteria (LAB). This study aimed to isolate efficient XOSs-fermenting probiotic LAB from ethnic pickled bamboo shoot products. A total of 51 XOSs-fermenting LAB were recovered from 24 samples of Naw Mai Dong, while 17 strains exhibited luxuriant growth in xylose and XOSs. Among these, seven strains belonging to Levicaseibacillus brevis and Pediococcus acidilactici exhibited similar growth in glucose, xylose, and XOSs, while the rest showed a weaker degree of growth in xylose and XOSs than glucose. Sixteen strains exhibited resistance under gastrointestinal tract conditions and displayed antimicrobial activity against foodborne pathogens. Notably, Lv. brevis FS2.1 possessed the greatest probiotic properties, with the highest %hydrophobicity index and %auto-aggregation. Effective degradation and utilization of XOSs by probiotic strains are dependent upon xylanase and β-xylosidase production, as well as xylose metabolism. It can be concluded that pickled bamboo shoot products can be a beneficial source of XOSs-fermenting probiotic LAB.

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

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

Enterococcus faecium s6 Enabled Efficient Homofermentative Lactic Acid Production from Xylan-Derived Sugars

A thermotolerant Enterococcus faecium s6 strain exhibited homoferementative lactic acid (LA) production at high xylose concentration (≥50 g/L). In batch fermentation at 45 °C and controlled pH of 6.5, strain E. faecium s6 produced up to 72.9 g/L of LA with a yield of 0.99 g/g-consumed xylose and productivity of 1.74 g/L.h from 75 g/L xylose. An increased LA concentration and productivities with high yields were obtained in repeated batch fermentation that was conducted for 24 runs. In this mode, the strain could produce LA up 81.1 g/L within 5 h fermentation at a high productivity of 13.5 g/L.h and a yield of 1.02 g/g-consumed xylose. The strain was unable to consume birchwood xylan as sole carbon source. However, it could efficiently utilize xylooligosaccharides of xylobiose, xylotriose, xylotetraose, xylopentaose, and xylohexaose. The intracellular xylosidase activity was induced by xylose. Using xylooligosaccharide (50 g/L)/xylose (5 g/L) mixtures, the strain was able to produce maximum LA at 48.2 g/L within 120 h at a yield of 1.0 g/g-consumed sugar and productivity of 0.331 g/L.h. These results indicate that E. faecium s6 is capable of directly utilizing xylan-hydrolyzate and will enable the development of a feasible and economical approach to the production of LA from hemicellulosic hydrolysate.

Effect of Different Polymerized Xylooligosaccharides on the Metabolic Pathway in Bifidobacterium adolescentis

Metabolic pathway analysis of Bifidobacterium adolescent (B. adolescentis) grown on either xylobiose and xylotriose (X2/X3) or xylopentaose (X5) and identifying key regulatory-related genes and metabolites from RNA-seq and UHPLC system was performed. Compared with X5, X2/X3 highly promoted the growth of B. adolescentis. Also, the transcriptome analysis showed that a total of 268 differentially expressed genes (DEGs) of B. adolescentis cultured with X2/X3 and X5 were screened, including 163 upregulated and 105 downregulated genes (X2/X3 vs. X5), which mainly were ABC transporters. Furthermore, the qRT-PCR results of 16 DGEs validated the accuracy of the RNA-seq data. Meanwhile, metabolomics analysis showed that 192 differential metabolites noted on MS2 included 127 upregulated and 65 downregulated metabolites; mainly, metabolites were amino acids and organic acids. The abundance difference of specific genes and metabolites highlighted regulatory mechanisms involved in utilizing different polymerized xylooligosaccharides by B. adolescentis.

One-step fermentation for producing xylo-oligosaccharides from wheat bran by recombinant Escherichia coli containing an alkaline xylanase

BACKGROUND

One-step fermentation is a cheap way to produce xylo-oligosaccharides (XOS), where production of xylanases and XOS is integrated into a single process. In spite of cost advantage, one-step fermentation is still short in yield so far due to the limited exploration. To cope with this issue, production of XOS from wheat bran by recombinant Escherichia coli through one-step fermentation was investigated in this study.

RESULTS

An endo-β-1,4-xylanase gene belonging to glycoside hydrolase family 11 of Bacillus agaradhaerens was employed to construct recombinant E. coli. This xylanase showed maximal activity at 60 °C and pH 8.0-8.5. Its activity retained more than 60% after incubation at 70 °C for 4 h, showing a good stability. The recombinant E. coli BL21(DE3) could secreted xylanases that directly hydrolyzed de-starched wheat bran to XOS in fermentation medium. The XOS generated from hydrolysis consisted of xylose, xylobiose and xylotriose accounting for 23.1%, 37.3% and 39.6%, respectively. Wheat bran concentration was found to be the most crucial factor affecting XOS production. The XOS concentration reached 5.3 mg/mL at 10% loading of wheat bran, which is higher than those of previous researches. Nitrogen source type could also affect production of XOS by changing extracellular xylanase activity, and glycine was found to be the best one for fermentation. Optimal fermentation conditions were finally studied using response surface optimization. The maximal concentration emerged at 44.3 °C, pH 7.98, which is affected by characteristics of the xylanase as well as growth conditions of E. coli.

CONCLUSIONS

This work indicates that the integrated fermentation using recombinant E. coli is highly competitive in cost and final concentration for producing XOS. Results can also provide theoretical basis for large-scale production and contribute to the wide adoption of XOS.

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

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

Recent progress on n-butanol production by lactic acid bacteria

n-Butanol is an essential chemical intermediate produced through microbial fermentation. However, its toxicity to microbial cells has limited its production to a great extent. The anaerobe lactic acid bacteria (LAB) are the most resistant to n-butanol, so it should be the first choice for improving n-butanol production. The present article aims to review the following aspects of n-butanol production by LAB: (1) the tolerance of LAB to n-butanol, including its tolerance level and potential tolerance mechanisms; (2) genome editing tools in the n-butanol-resistant LAB; (3) methods of LAB modification for n-butanol production and the production levels after modification. This review will provide a theoretical basis for further research on n-butanol production by LAB.

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

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

Polysaccharide Derived from Nelumbo nucifera Lotus Plumule Shows Potential Prebiotic Activity and Ameliorates Insulin Resistance in HepG2 Cells

Polysaccharides are key bioactive compounds in lotus plumule tea, but their anti-diabetes activities remain unclear. The purpose of this study was to investigate the prebiotic activities of a novel polysaccharide fraction from the Nelumbo nucifera lotus plumule, and to examine its regulation of glucose metabolism in insulin-resistant HepG2 cells. The N. nucifera polysaccharide (NNP) was purified after discoloration, hot water extraction, ethanol precipitation, and DEAE-cellulose chromatography to obtain purified polysaccharide fractions (NNP-2). Fourier transform infrared spectroscopy was used to analyze the main structural characteristics and functional group of NNP-2. Physicochemical characterization indicated that NNP-2 had a molecular weight of 110.47 kDa and consisted of xylose, glucose, fructose, galactose, and fucose in a molar ratio of 33.4:25.7:22.0:10.5:8.1. The prebiotic activity of NNP-2 was demonstrated in vitro using Lactobacillus and Bifidobacterium. Furthermore, NNP-2 showed bioactivity against α-glucosidase (IC₅₀ = 97.32 µg/mL). High glucose-induced insulin-resistant HepG2 cells were used to study the effect of NNP-2 on glucose consumption, and the molecular mechanism of the insulin transduction pathway was studied using RT-qPCR. NNP-2 could improve insulin resistance by modulating the IRS1/PI3K/Akt pathway in insulin-resistant HepG2 cells. Our data demonstrated that the Nelumbo nucifera polysaccharides are potential sources for nutraceuticals, and we propose functional food developments from the bioactive polysaccharides of N. nucifera for the management of diabetes.