Enzymatic Properties of Recombinant Thermophilic Xylanase from Pseudothermotoga thermarum and Its Application in Beer Brewing

This study aimed to investigate the efficient expression of the xylanase gene Pthxyn of Pseudothermotoga thermarum and its application in beer brewing. The recombinant plasmid pET-20b-pthxyn was constructed and expressed in Escherichia coli. Pthxyn was purified. The molecular mass of the recombinant xylanase was 130 kDa, and the optimum reaction pH and temperature were 5.5 and 95 ℃, respectively. It retained 80% and 83% of its activity after incubation at pH 5.0–8.0 for 2 h, and at 75 ℃ for 1 h, respectively. In the saccharification stage of beer brewing, the recombinant xylanase was added to the reaction system consisting of barley or wheat as raw material at 65 ℃, and the products xylose and glucose were detected by high performance liquid chromatography (HPLC). The results showed that when barley was used as raw material, the xylose content increased from 0.017 to 1.25 g/L, and the glucose content increased from 20 to 36.57 g/L. When wheat was used as the raw material, xylose increased from 0.003 g/L to 0.708 g/L, and the glucose content increased from 21.9 g/L to 36.63 g/L. In summary, the recombinant xylanase is tolerant to a wide range of pH and stable to heat treatment, and can synergize with endogenous enzymes to improve its catalytic efficiency in the saccharification stage of beer brewing, making it have good prospects in beer brewing.