Optimised ultrasonic-assisted extraction of flavonoids from Folium eucommiae and evaluation of antioxidant activity in multi-test systems in vitro

The central composite design combined with response surface methodology was used to optimise ultrasonic-assisted extraction for flavonoids-enriched extract from Folium eucommiae. The results indicate that the highest extraction ratio of flavonoids by ultrasonic-assisted extraction could arrive 17.2% using 40% ethanol as solvent and 1:60 solid to lipid ratio for 70 min extraction, which was more efficient than that by heating, microwaves-assisted and enzyme-assisted extractions. The crude extract was then purified by macroporous adsorption resin, the flavonoids content in the purified extract increased to 78.6%. The flavonoids-enriched extract exhibited quite strong reducing property as well as the total antioxidant capacity, and excellent inhibitions of hydroxyl radical, superoxide radical, the haemolysis of rat erythrocytes and the generation of MDA of rat organ tissue. Meanwhile, it was found that the bioactivities appeared to be dose-dependent of flavonoids.