Optimization of ultrasonic extraction of phenolic compounds from Euryale ferox seed shells using response surface methodology

The ultrasound-assisted extraction of phenolic compounds from Euryale ferox seed shells was modeled using response surface methodology. A three-level-three-factor Box–Behnken design was employed to optimize three extraction variables, including extraction time ( X 1 ), ethanol concentration ( X 2 ), and ratio of aqueous ethanol to raw material ( X 3 ), for the achievement of high extraction yield of the phenolic compounds. The statistical analyses show that the independent variables ( X 1 , X 2 ), the quadratic terms ( X 1 2 $X_1^2$ , X 2 2 $X_2^2$ and X 3 2 $X_3^2$ ), and the interactions of X 1 with X 2 and X 3 have significant effect on the yield ( p   <   0.01). The optimized conditions are X 1 of 21   min, X 2 of 52%, and X 3 of 31   mL/g. Under these conditions, the experimental yield is 15.69   ±   0.082% ( n   =   3), which is well matched with the predicted yield of 15.70%. The evaluation of antioxidant activity by DPPH assay indicates that the phenolic compounds from E. ferox seed shells possess significant antioxidant activity. HPLC analysis reveals that pyrogallol, gallic acid, chlorogenic acid and rutin are the major composition in the extracts.