Enhanced extraction of bioactive natural products using ultrasound-assisted aqueous two-phase system: Application to flavonoids extraction from jujube peels

The ultrasound-assisted aqueous two-phase extraction (UA-ATPE) was employed to develop an effective technique for the extraction of flavonoids from jujube peels (JPs). The extraction conditions were further optimized as K2HPO4 35% (w/w), ethanol 20% (w/w), solid–liquid ratio 1:30 g/mL (w/v), ultrasonic power 200 W, and extraction time 50 min. Moreover, rutin, quercetin 3-β-d-glucoside, and kaempferol-3-O-rutinosid were identified as the main flavonoids by UPLC-MS/MS. Finally, the extraction mechanism of UA-ATPE was explored, which is salting out effect, hydrogen bonding, van der Waals force, and ultrasound promoted the mass transfer of solvent to cells of JPs, then extraction behavior occurred. The mechanical destruction of JPs cells by ultrasound also further accelerated the release of flavonoids. Flavonoids were captured by W/W emulsion in the bottom phase and distributed to the top phase. Overall, this study proposes a green and clean method, UA-ATPE, to extract flavonoids from JPs, while revealing the mechanism of UA-ATPE.