Co-expression of α-L-rhamnosidase and β-glucosidase in Aspergillus niger and its application in enzymatic production of quercetin

Quercetin (3,3',4',5,7-pentahydroxy flavonoid) is a bioactive flavonoid with significant medicinal properties. Similarly, Rutin (quercetin-3-O-rutinoside or 3',4',5,7-tetrahydroxy-flavone-3-rutinoside) is widely recognized flavonoid, and is converted to quercetin by α-L-rhamnosidase and β-D-glucosidase. In this study, engineered Aspergillus niger co-expressing α-L-rhamnosidase and β-glucosidase was successfully constructed, and engineered strain Rha1-BGL8 was obtained by enzyme activity assay. When submerged fermentation after 120 h in 5 L of fermenter, the α-L-rhamnosidase activity was 36.90 U/mL and β-glucosidase activity was 61.02 U/mL. The fermented complex enzyme solution was employed for the hydrolysis of rutin to quercetin, and the yield of quercetin reached 95.31 % after 48 h, molecular structure of quercetin was verified by highly specific chromatographic methods. This study lays a technical foundation for the potential industrial application of enzyme-catalyzed conversion of rutin to quercetin.