Enhanced extraction of flavonoids from Astragali Radix by steam explosion

The flavonoids in Astragali Radix (AR) exhibited various biological activities, but the extraction efficiency is low due to the rigid binding structure of plant cell walls. This study investigated the effects of steam explosion (SE) on the physicochemical properties and flavonoid extraction of AR. Variation in lignin, cellulose and hemicellulose content suggested the modification of cellular structure. Decrease in crystallinity index, and changes in specific surface area and pore size implied the rigid structure of cell walls was destroyed. Microscopy observation further validated the tissue disruption, fiber fragmentation and structural loosening. Specifically, the maximum flavonoid content was obtained from AR treated by SE (1 MPa, 20 min), which was 4.36 times higher than the control. In summary, SE treatment at relatively low operating pressure with prolonged holding time disrupted the compact cell wall structure and significantly enhanced flavonoid extraction, demonstrating substantial application potential for herbal medicine processing. • SE (1 MPa, 20 min) promoted flavonoids extraction of Astragali Radix by 4.36-fold. • SE altered cell wall morphology, chemical components and physical properties. • SE was proven to be an effective approach for enhancing flavonoids extraction.