Ultrasound-assisted process for optimal recovery of phenolic compounds from watermelon (Citrullus lanatus) seed and peel

Ultrasound-assisted extraction (UAE) was optimized for the collection of phenolic compounds and determination of antioxidant activity of watermelon peel (WMP) and watermelon seed (WMS) using Box-Behnken design and response surface methodology. UAE process variables (sonication temperature, sonication time, and ethanol concentration) had a significant impact on the total phenolic content (TPC) and antiradical activity of WMP and WMS. The optimum conditions for WMP extraction (sonication temperature = 47.82 °C, sonication time = 31.63 min, and ethanol concentration = 42.84%) yielded maximum TPC (7.944 mg GAE/100 mL) and antiradical activity (85.150%) while UAE at 50.32 °C, 37.60 min, and 39.18% ethanol yielded maximum TPC (32.152 mg GAE/100 mL) and antiradical activity (85.947%) for WMS. The experimental values obtained matched well with the predicted values. Furthermore, of the nine phenolic acids studied, eight were identified and quantified by GC–MS analysis in WMS extracts while none were identified in WMP extracts.