Improved secretory expression and characterization of thermostable xylanase and β-xylosidase from Pseudothermotoga thermarum and their application in synergistic degradation of lignocellulose

Advances of microbial xylanases in the application of flour industries: A comprehensive review

Microbial xylanase has a wide range of applications, and many researchers favoring its utilization as an alternative to improve flour products. Wheat flour is the main raw material of flour products, although the content of arabinoxylan is not high in flour products, but it has a great influence on the quality of flour products, microbial xylanase can act on wheat arabinoxylan, so as to play the role of flour product improvement. This review carries out a description of the research progress on the application of xylanases in flour products in terms of xylanase properties, different families of xylanases and improvement mechanisms of xylanases in flour products. According to the properties of various microbial sources of xylanases, the suitable xylanase can be added to flour products, and the effect of xylanase towards wheat arabinoxylan in flour can be used to improve the quality of flour products. The molecular modification based on the properties of xylanase and the crystal structure of different families of xylanase and their substrate specificity toward wheat arabinoxylan are discussed. The article reviews the information about microbial xylanases in order to achieve better results in flour products and to provide a theoretical basis for their industrial application.

Citric Acid by-Product Fermentation by Bacillus subtilis I9: A Promising Path to Sustainable Animal Feed

Citric acid by-products in animal feed pose a sustainability challenge. Bacillus species are commonly used for fermenting and improving the nutritional quality of feedstuffs or by-products. An experiment was conducted to enhance the nutritional value of citric acid by-products through fermentation with Bacillus subtilis I9 for animal feed. The experiment was carried out in 500 mL Erlenmeyer flasks with 50 g of substrate and 200 mL of sterile water. Groups were either uninoculated or inoculated with B. subtilis I9 at 107 CFU/mL. Incubation occurred at 37 °C with automatic shaking at 150 rpm under aerobic conditions for 0, 24, 48, 72, and 96 h. Inoculation with B. subtilis I9 significantly increased Bacillus density to 9.3 log CFU/mL at 24 h (p < 0.05). CMCase activity gradually increased, reaching a maximum of 9.77 U/mL at 72 h. After 96 h of fermentation with inoculated B. subtilis I9, the citric acid by-product exhibited a significant decrease (p < 0.05) in crude fiber by 10.86%, hemicellulose by 20.23%, and cellulose by 5.98%, but an increase in crude protein by 21.89%. Gross energy decreased by 4% after inoculation with B. subtilis in comparison to the uninoculated control (p < 0.05). Additionally, the non-starch polysaccharide (NSP) degradation due to inoculation with B. subtilis I9 significantly reduced (p < 0.05) NSP by 24.37%, while galactose, glucose, and uronic acid decreased by 22.53%, 32.21%, and 18.11%, respectively. Amino acid profile content increased significantly by more than 12% (p < 0.05), including indispensable amino acids such as histidine, isoleucine, lysine, methionine, phenylalanine, tryptophan, and valine and dispensable amino acids like alanine, aspartic acid, glutamic acid, glutamine, glycine, proline, and tyrosine. Furthermore, citric acid by-products inoculated with B. subtilis I9 exhibited changes in the cell wall structure under scanning electron microscopy, including fragmentation and cracking. These results suggest that fermenting citric acid by-products with B. subtilis I9 effectively reduces dietary fiber content and improves the nutritional characteristics of citric acid by-products for use in animal feed.

A novel endo-1,4-β-xylanase from Alicyclobacillus mali FL18: Biochemical characterization and its synergistic action with β-xylosidase in hemicellulose deconstruction

A novel endo-1,4-β-xylanase-encoding gene was identified in Alicyclobacillus mali FL18 and the recombinant protein, named AmXyn, was purified and biochemically characterized. The monomeric enzyme worked optimally at pH 6.6 and 80 °C on beechwood xylan with a specific activity of 440.00 ± 0.02 U/mg and a good catalytic efficiency (kcat/KM = 91.89 s-1mLmg-1). In addition, the enzyme did not display any activity on cellulose, suggesting a possible application in paper biobleaching processes. To develop an enzymatic mixture for xylan degradation, the association between AmXyn and the previously characterized β-xylosidase AmβXyl, deriving from the same microorganism, was assessed. The two enzymes had similar temperature and pH optima and showed the highest degree of synergy when AmXyn and AmβXyl were added sequentially to beechwood xylan, making this mixture cost-competitive and suitable for industrial use. Therefore, this enzymatic cocktail was also employed for the hydrolysis of wheat bran residue. TLC and HPAEC-PAD analyses revealed a high conversion rate to xylose (91.56 %), placing AmXyn and AmβXyl among the most promising biocatalysts for the saccharification of agricultural waste.