Microwave-assisted extraction of flavonoids from tender leaves of Lithocarpus polystachyus Rehd

A high efficient and environment-friendly technology for extracting flavonoids from Lithocarpus polystachyus is needed. The effects of flavonoids extraction by microwave-assisted extraction in water (MW) and in Ca(OH)₂ solution(MCW), immersion in water(W) and in Ca(OH)₂ solution(CW), refluxing of ethanol(E) and methanol(Me) were compared; the conditions of MCW were optimized by orthogonal experiment; also the relationship between material pre-boiling and microwave treating time, and the influences of Ca(OH)₂ concentration on the result of MCW were studied. Results show that the extraction effect of MCW is remarkably better than that of W, CW, MW, E and Me, and the extraction effect of MCW is significantly promoted by the material pre-boiling and the moderate Ca(OH)₂ concentration. The optimum conditions of MCW are defined as follows: Ca(OH)₂ concentration of 1.2%, solid to liquid ratio of 1∶12, pre-boiling 5 min, microwave treating 25 min by the microwave oven at high grade of power. Under these conditions, 96% of extraction rate and 37% of flavonoids content are reached, and thus it is a high efficient and environment-friendly technology for extracting flavonoids from Lithocarpus polystachyus Rehd.