The objective of this study was to optimize the extraction conditions of phenolic and flavonoids compounds from quinoa (Chenopodium quinoa) seeds using ultrasound assistance technology. A randomized central composite face-centered design was used to evaluate the effect of extraction temperature, ethanol concentration in the solvent, and ultrasound power on the total phenolic content (TPC), total flavonoid content (TFC) and antioxidant activity by response surface analysis. Predicted model equations were obtained to describe the experimental data regarding TPC, TFC and antioxidant activity, with significant variation in the linear, quadratic, and interaction effects of the independent variables. Regression analysis showed that more than 88 % of the variability was explained by the models. The best extraction conditions obtained by simultaneous maximization of the responses were: extraction temperature of 60 °C, 80 % ethanol as solvent and non-application of ultrasounds. Under the optimal conditions, the corresponding predicted response values were 103.6 mg GAE/100 g dry weight (dw), 25.0 mg quercetin equiv./100 g dw and 28.6 % DPPH radical scavenging, for TPC, TFC and antioxidant activity, respectively. The experimental values agreed with those predicted within a 95 % confidence level, indicating the suitability of the employed model. HPLC analysis of the obtained extracts confirmed the highest phenolic compound yield in the extract obtained under optimal extraction conditions. Considering the characteristics of the antioxidant-rich extracts obtained, they could be consider for potential application in the food industry, as nutraceutical and functional foods ingredient or well as replacement of synthetic antioxidants.
