Ultrasound-assisted aqueous two-phase extraction of flavonoids from erigeron breviscapus: process optimization, structural characterization, antioxidant study, and DFT calculation

The well-known medicinal plant Erigeron breviscapus has long been used to treat cerebral embolism, cerebral thrombosis, and cerebral hemorrhage. Response surface methodology (RSM) was applied to optimize the ultrasonic-assisted extraction process of total flavonoids from Erigeron breviscapus (EBTF) using aqueous two-phase system. The flavonoids from E. breviscapus were qualitatively identified using UPLC-Q-TOF-MS/MS. The capacity of EBTF to scavenge ·OH was used to assess its antioxidant activity. To determine the active sites in the primary bioactive components that scavenge ·OH, density functional theory (DFT) calculations were conducted. Total flavonoid content (TFC) from E. breviscapus was 48.53 mg/g under ideal conditions with PEG2000 mass fraction of 16%, (NH₄)₂SO₄ mass fraction of 14%, ultrasound time of 41 min, and liquid-solid ratio of 35 mL/g. 28 flavonoids have been tentatively identified in E. breviscapus via ultra-high-performance liquid chromatography coupled with quadrupole time-of-flight mass spectrometry (UPLC-Q-TOF-MS/MS). Furthermore, EBTF demonstrated moderate hydroxyl radical scavenging capacity, with scavenging rate of 60.68% at 3.9 mg/mL. The 6-OH site of scutellarin was the core active site for scavenging hydroxyl radicals. The findings provide both theoretical and experimental support for the in-depth development of EBTF as a natural antioxidant.