Optimization of phenol compound extraction and antioxidant activity of Pistacia khinjuk fruits by ultrasonic waves based on a Response Surface Methodology

In the present study, the optimization process of phenolic compounds extraction and antioxidant activity (DPPH radical-scavenging assay, FRAP test, and oxidative stability index) of Pistacia khinjuk fruits was evaluated using ultrasound waves through response surface methodology (RSM). To optimize the extraction process from the central composite design with three independent variables including time (5, 27.5 and 50 minutes), temperature (25, 45 and 65 ° C) and ethanol ratio in water-ethanol solvent (0, 50 and 100% ) was used. Significant effects of independent variables on the extraction of phenol compound, DPPH radical scavenging power, FRAP test and OSI of P.khinjuk fruit extract, with the regression coefficients of 97.65, 98.09, 98.62 and 98.38 %, respectively, were noted. Among the independent parameters, ethanol concentration was the most effective parameter because two effects of quadratic and linear were observed in the proposed models of different tests. The interaction effect between different paprameters was not observed in the models of this study, too. It was also the strongest model for the phenolic compounds extraction test; because in this test, in addition to the linear effect of independent parameters that were common to all tests, a quadratic effect was also observed in the parameters of time and ethanol concentration. Also, the best antioxidant activity of P.khinjuk fruit was obtained by using the ultrasonic wave for 50 minutes at 65 ºC and with 57.7% v/v ethanol/water solution. Finally, it was found that the results of experimental tests were close to the values predicted by the response level method.