Green and efficient extraction of bioactive flavonoids from Equisetum palustre L. by deep eutectic solvents-based negative pressure cavitation method combined with macroporous resin enrichment

In the present study, deep eutectic solvents (DESs) as new extraction solvents, are proposed for the green and efficient extraction and separation of bioactive flavonoids from Equisetum palustre L. with negative pressure cavitation-assisted extraction (NPCE) combined with macroporous resin enrichment. A series of different DES systems were investigated for the extraction of bioactive flavonoids in E. palustre. Compared with conventional extraction solvents, DES composed of choline chloride/betaine hydrochloride-ethylene glycol possessed a more effective extraction yields. In addition, the DES-NPCE extraction procedures were also optimized systematically. The optimal conditions were obtained as follows: choline chloride-betaine hydrochloride-ethylene glycol formed a DES with the mole ratio of 1:1:2, 20% water content, extraction pressure −0.07 MPa, extraction temperature 60°C, solvent to solid ratio 25:1 mL/g, and the extraction time 20 min. Furthermore, the direct enrichment of nine flavonoids in DES extraction solution were efficiently achieved using macroporous resin HPD-826. The contents of the nine target flavonoids separated by HPD-826 resin were from 0.17% to 3.37%, and the recovery yields from 57.14% to 89.25%. In conclusion, the developed DES-NPCE combined with macroporous resin enrichment can be an alternative procedure for the green and efficient extraction and separation of bioactive flavonoids from plant sample matrices.