Heterologous Expression of a Thermostable Arabinoxylan Specific Xylanase from Paecilomyces thermophila and Its Application in Malt Mashing

Objective: This study aimed to identify thermostable xylanase suitable for mash malting. Methods: A xylanase encoding gene (PtXynA) from Paecilomyces thermophila J18 was cloned and heterologously expressed in Aspergillus niger. A submerged fermentation in a 5 L fermentor was performed for the production of the recombinant enzyme (PtXynA). The enzymatic properties of PtXynA were characterized and its application potential in mash malting was further evaluated. Results: A maximum extracellular xylanase activity of 904.0 U/mL with a protein content of 1.4 mg/mL was obtained after 96 h of fermentation. PyXynA was most active at pH7.0 and 70 ℃, respectively, and it was stable within the pH range of 5.5~9.0 and at temperatures below 75 ℃. The enzyme displayed strict substrate specificity towards various xylans, with the highest specific activity towards wheat arabinoxylan (1993.2 U/mg), followed by oat spelt xylan (1782.5 U/mg), beechwood xylan (1552.0 U/mg) and birchwood xylan (1238.7 U/mg). The addition of PtXynA in mash (200 U/g malt) reduced the filtration time and viscosity of malt by 43.9% and 10.8%, respectively. Conclusion: The excellent properties may enable PyXynA great application potential in beer industry.