Green and efficient extraction of four bioactive flavonoids from Pollen Typhae by ultrasound-assisted deep eutectic solvents extraction

Recently, deep eutectic solvents (DESs) have been recognized as a novel class of sustainable solvents to replace common organic solvents. In this study, a highly and efficient extraction technique for determination of four bioactive flavonoids from Pollen Typhae using a combination of ultrasound-assisted extraction and natural deep eutectic solvents (NADESs) was developed. A series of DESs containing various hydrogen bond acceptors combined with different hydrogen bond donors were synthesized and screened for high extraction efficiencies based on the flavonoids extraction yields. The extraction conditions including composition of DES, water content in DES, liquid-solid ratio, and extraction time were statistically optimized by single-factor experiment. As a result, DES composed of choline chloride and 1,2-propanediol (ChPri) at 1:4 M ratio, 30% of aqueous solution, 50:1 mg mL-1 for solid-liquid ratio, and 35 min for extraction time were selected as the most effective process for extraction of flavonoids in Pollen Typhae. Under the optimal conditions, the target compounds recoveries were in the range of 86.87%-98.89%. Meanwhile, DESs showed greater extraction efficiency for extraction of quercetin, naringenin, kaempferol and isorhamnetin from Pollen Typhae comparing with conventional solvents such as methanol and 75% of aqueous ethanol. Comparing DESs to the conventional organic solvents, in addition to their reduced environmental impacts, they proved to provide higher extraction efficiency for flavonoids, and therefore have a great potential as possible alternatives to those organic solvents in extraction of Chinese herbal medicines.