Advances in the understanding of the production, modification and applications of xylanases in the food industry

Xylanases have broad applications in the food industry to decompose the complex carbohydrate xylan. This is applicable to enhance juice clarity, improve dough softness, or reduce beer turbidity. It can also be used to produce prebiotics and increase the nutritional value in foodstuff. However, the low yield and poor stability of most natural xylanases hinders their further applications. Therefore, it is imperative to explore higher-quality xylanases to address the potential challenges that appear in the food industry and to comprehensively improve the production, modification, and utilization of xylanases. Xylanases, due to their various sources, exhibit diverse characteristics that affect production and activity. Most fungi are suitable for solid-state fermentation to produce xylanases, but in liquid fermentation, microbial metabolism is more vigorous, resulting in higher yield. Fungi produce higher xylanase activity, but bacterial xylanases perform better than fungal ones under certain extreme conditions (high temperature, extreme pH). Gene and protein engineering technology helps to improve the production efficiency of xylanases and enhances their thermal stability and catalytic properties.

Cloning and characterization of a novel mesophilic xylanase gene Fgxyn3 from Fusarium graminearum Z-1

In order to search for high specific activity and the resistant xylanases to XIP-I and provide more alternative xylanases for industrial production, a strain of Fusarium graminearum from Triticum aestivum grains infected with filamentous fungus produced xylanases was isolated and identified. Three xylanase genes from Fusarium graminearum Z-1 were cloned and successfully expressed in E. coli and P. pastoris, respectively. The specific activities of Fgxyn1, EFgxyn2 and EFgxyn3 for birchwood xylan were 38.79, 0.85 and 243.83 U/mg in E. coli, and 40.11, 0 and 910.37 U/mg in P. pastoris, respectively. EFgxyn3 and PFgxyn3 had the similar optimum pH at 6.0 and pH stability at 5.0-9.0. However, they had different optimum temperature and thermal stability, with 30 °C for EFgxyn3 and 40 °C for PFgxyn3, and 4-35 °C for EFgxyn3 and 4-40 °C for PFgxyn3, respectively. The substrate spectrum and the kinetic parameters showed that the two xylanases also exhibited the highest xylanase activity and catalytic efficiency (kcat/km) toward birchwood xylan, with 243.83 U/mg and 61.44 mL/mg/s for EFgxyn3 and 910.37 U/mg and 910.37 mL/mg/s for PFgxyn3, respectively. This study provided a novel mesophilic xylanase with high specific activity and catalytic efficiency, thus making it a promising candidate for extensive applications in animal feed and food industry.

Supplementary Information

The online version contains supplementary material available at 10.1007/s13205-024-03973-0.

Enhancing the acid stability of the recombinant GH11 xylanase xynA through N-terminal substitution to facilitate its application in apple juice clarification

The utilization of xylanase in juice clarification is contingent upon its stability within acidic environments. We generated a mutant xynA-1 by substituting the N-terminal segment of the recombinant xylanase xynA to investigate the correlation between the N-terminal region of xylanase and its acid stability. The enzymatic activity of xynA-1 was found to be superior under acidic conditions (pH 5.0). It exhibited enhanced acid stability, surpassing the residual enzyme activity values of xynA at pH 4.0 (53.07 %), pH 4.5 (69.8 %), and pH 5.0 (82.4 %), with values of 60.16 %, 77.74 %, and 87.3 %, respectively. Additionally, the catalytic efficiency of xynA was concurrently improved. Through molecular dynamics simulation, we observed that N-terminal shortening induced a reduction in motility across most regions of the protein structure while enhancing its stability, particularly Lys131-Phe146 and Leu176-Gly206. Furthermore, the application of treated xynA-1 in the process of apple juice clarification led to a significant increase in clarity within a short duration of 20 min at 35 °C while ensuring the quality of the apple juice. This study not only enhances the understanding of the N-terminal region of xylanase but also establishes a theoretical basis for augmenting xylanase resources employed in fruit juice clarification.

Significantly Enhanced Thermostability of Aspergillus niger Xylanase by Modifying Its Highly Flexible Regions

In this study, the thermostability of an acid-resistant GH11 xylanase (xynA) from Aspergillus niger AG11 was enhanced through systematic modification of its four highly flexible regions (HFRs) predicted using MD simulations. Among them, HFR I (residues 92-100) and HFR II (residues 121-130) were modified by iterative saturation mutagenesis (ISM), yielding mutants G92F/G97S/G100K and T121V/A124P/I126V/T129L/A130N, respectively. For HFR III, the N-(residues 1-37) and C-termini (residues 179-188) were, respectively, substituted with the corresponding sequences from thermophilic EvXyn11^TS and Nesterenkonia xinjiangensis xylanase. N-Glycosylation was introduced into HFR IV (residues 50-70) through site-directed mutation (A55N/D57S/S61N) and the recombinant expression in A. niger AG11. Combining these positive mutations from each HFR yielded the variant xynAm1 with 137.6- and 1.3-fold increases in half-life at 50 °C and specific activity compared to the wild-type xynA, respectively. With the highest thermostability at 80 and 90 °C in reports, xynAm1 could be a robust candidate for industrial applications in functional foods, feed products, and bioethanol production.

Co-production of Xylooligosaccharides and Xylose From Poplar Sawdust by Recombinant Endo-1,4-β-Xylanase and β-Xylosidase Mixture Hydrolysis

As is well-known, endo-1,4-β-xylanase and β-xylosidase are the rate-limiting enzymes in the degradation of xylan (the major hemicellulosic component), main functions of which are cleavaging xylan to release xylooligosaccharides (XOS) and xylose that these two compounds have important application value in fuel, food, and other industries. This study focuses on enzymatic hydrolysis of poplar sawdust xylan for production of XOS and xylose by a GH11 endo-1,4-β-xylanase MxynB-8 and a GH39 β-xylosidase Xln-DT. MxynB-8 showed excellent ability to hydrolyze hemicellulose of broadleaf plants, such as poplar. Under optimized conditions (50°C, pH 6.0, dosage of 500 U/g, substrate concentration of 2 mg/mL), the final XOS yield was 85.5%, and the content of XOS₂₋₃ reached 93.9% after 18 h. The enzymatic efficiency by MxynB-8 based on the poplar sawdust xylan in the raw material was 30.5%. Xln-DT showed excellent xylose/glucose/arabinose tolerance, which is applied as a candidate to apply in degradation of hemicellulose. In addition, the process and enzymatic mode of poplar sawdust xylan with MxynB-8 and Xln-DT were investigated. The results showed that the enzymatic hydrolysis yield of poplar sawdust xylan was improved by adding Xln-DT, and a xylose-rich hydrolysate could be obtained at high purity, with the xylose yield of 89.9%. The enzymatic hydrolysis yield was higher (32.2%) by using MxynB-8 and Xln-DT together. This study provides a deep understanding of double-enzyme synergetic enzymolysis of wood polysaccharides to valuable products.

Recent Development of Extremophilic Bacteria and Their Application in Biorefinery

The biorefining technology for biofuels and chemicals from lignocellulosic biomass has made great progress in the world. However, mobilization of laboratory research toward industrial setup needs to meet a series of criteria, including the selection of appropriate pretreatment technology, breakthrough in enzyme screening, pathway optimization, and production technology, etc. Extremophiles play an important role in biorefinery by providing novel metabolic pathways and catalytically stable/robust enzymes that are able to act as biocatalysts under harsh industrial conditions on their own. This review summarizes the potential application of thermophilic, psychrophilic alkaliphilic, acidophilic, and halophilic bacteria and extremozymes in the pretreatment, saccharification, fermentation, and lignin valorization process. Besides, the latest studies on the engineering bacteria of extremophiles using metabolic engineering and synthetic biology technologies for high-efficiency biofuel production are also introduced. Furthermore, this review explores the comprehensive application potential of extremophiles and extremozymes in biorefinery, which is partly due to their specificity and efficiency, and points out the necessity of accelerating the commercialization of extremozymes.