Optimization of the ultrasound-assisted extraction of flavonoids and the antioxidant activity of Ruby S apple peel using the response surface method

A Box–Behnken Design (BBD) was employed to optimize the extraction of antioxidants from Ruby S apple peel by ultrasound-assisted extraction (UAE). The effect of extraction temperature (20–40 °C), extraction time (15–45 min), and ethanol concentration (50–90%) in water on extraction yield, total phenol content (TPC), total flavonoid content (TFC), and DPPH radical scavenging activity of Ruby S peel extracts (RPEs) were investigated. The optimized extraction conditions that maximized extraction yield, TPC, TFC, and DPPH radical scavenging ability, were temperature 20 °C, extraction time 25.30 min, and ethanol concentration 50%. The validity of designed model was verified, and experimental values obtained under optimum conditions concurred with predicted values. Hyperoside, isoquercitrin, and phloridzin, were among the major flavonoids extracted. Our findings demonstrate the suitability of UAE and RSM for the optimization of Ruby S peel extraction and suggest the potential use of RPEs as bioactive functional materials.