Onion peels are a rich source of antioxidant compounds that have beneficial effects on human health. This study was conducted to optimize the ultrasound-assisted extraction (UAE) conditions for the extraction of phenolics from onion peels using response surface methodology (RSM). The optimized conditions were compared with maceration extraction (MAE) methods. A Box-Behnken design was employed to develop the following three extracting parameters: ethanol concentration (X1: 40∼80%), extraction time (X2: 10∼50 min), ultrasonic power (X3: 150∼250 W). The optimum extraction conditions of 1,1-diphenyl-2-picrylhydrazyl (38.1 mg Trolox equivalent/g dw) and 2,2-azino-bis-3-ethylbenzothiazoline-6-sulfonic acid (77.8 mg Trolox equivalent/g dw) radical scavenging activities and total phenolic content (76.0 mg gallic acid equivalent/g dw) were obtained at X1=56.8%, X2=36.4 min, and X3=200.8 W. The predicted results matched well with the experimental results obtained using the optimal extraction conditions, which validated the RSM model with a good correlation. Finally, UAE showed greater extraction efficiency than MAE.

Keywords: optimization, ultrasound-assisted extraction, onion peel, response surface methodology, antioxidant