Abstract: In this work, ionic liquids (ILs) were used as extraction solvents to extract, separate and purify flavonoids from citrus peel by successive ultrasound-assisted extraction and aqueous two-phase extraction. Among nine ILs tested, it was found that tributylhexylphosphonium bromide ([P4446]Br) gave the highest yield (56.15 mg/g) of flavonoids from citrus peel. Using single factor experiments and response surface methodology, the optimum extraction conditions were determined as follows: [P4446]Br concentration 54%, solid-to-liquid ratio 1:10 (g/mL), extraction temperature 50 ℃, and ultrasonication time 10 min. Under these optimum conditions, the yield of flavonoids was 69.13 mg/g. After the ultrasound-assisted extraction, an aqueous two-phase system of [P4446]Br and sodium citrate was constructed by adding sodium citrate and used to further separate and purify the extracted flavonoids. The results showed that the extraction efficiency of flavonoids reached 98.20% when the tether length was 71.95 and the phase ratio was 1.13. After the aqueous two-phase extraction, butyl alcohol was used to back extract the flavonoids with a recovery of 80.11%.

Key words: citrus peel, flavonoid, ionic liquid, aqueous two-phase system, extraction and separation