Optimization of Process on Extracting Flavonoids from Dry Onion Skins by Alkaline Method

The flavonoids in dry onion skins were extracted by alkaline solution method. On the basis of single factor combined with ternary quadratic regression general rotary unitized design, the effects of several extraction parameters on the extraction efficiency of total flavonoids were investigated, including extraction times, pH of the extraction solution, material / extraction solution ratio, extraction time, and temperature. NaNO2-Al(NO3)3-NaOH method was used for the determination of total flavonoids. The optimal extraction conditions were as follows: two times of extraction; pH, 11; material / extraction solution ratio, 30 : 1; extraction temperature, 83.0 ~ 84.0 ℃; extraction duration, 1.9 ~ 2.0 h. Under the above optimal conditions, the flavonoids extracted from dry onion skins yielded 2.82%.