Ultrasound assisted extraction of anthocyanins and total phenolic compounds from dried cob of purple waxy corn using response surface methodology

Ultrasound-assisted extraction of anthocyanins and total phenolic compounds from the dried cob of purple waxy corn was investigated using response surface methodology, where the process variables were ultrasound amplitude levels (25, 50, 100%) and different solvents (pure water, water–ethanol ratio 1:1, pure ethanol), using a sample–solvent ratio of 1:20, and extraction temperature of 65 °C for 30 min. Central composite face-centered design was used to determine optimum process conditions. The results showed that the overall optimal condition for simultaneous extraction of anthocyanins and phenolic compounds was obtained by using 50% water in water–ethanol mixed solvent as solvent and amplitude level of 50%. The optimal yields of anthocyanins and phenolic compounds were 240.161 μg cyanidin-3-glucoside/g dry sample and 27.662 mg gallic acid/g dry sample, respectively. The result for the antioxidant activity of the extract obtained from this optimal extraction condition to decrease the initial DPPH• concentration by 50% was approximately 4.64 mg/ml.