Comprehensive understanding of impacts of steam explosion on facilitated extraction and transformation of flavonoids from Astragali Radix

Recalcitrant structure of cell walls restricts the extraction of bioactive components from edible plants. In this study, the impacts of steam explosion (SE) on the release and transformation of flavonoids in Astragali Radix (AR) were evaluated. Results revealed that SE destroyed the compact structure of cell walls. Furthermore, the porous network was reformed due to the degradation of hemicelluloses and water-soluble components. The maximum extraction contents of ethanol-soluble and water-soluble flavonoids of 6.34 and 1.48 mg/g were obtained from the pretreated AR (1.5 MPa, 5 min), which were 5.22 and 2.88 times higher than those obtained from the untreated AR, respectively. SE not only released bound flavonoids from cell walls by cleaving glycoside or ester bonds, but also transformed some flavonoid glycosides into aglycones through deglycosylation. In conclusion, SE can reduce mass transfer hindrance and facilitate flavonoid transformation, thus providing a green and facile processing method for traditional edible plants.