The phenolics from grapefruit peel were obtained by ultrasound assisted extraction (UAE) and enzyme-assisted extraction (EAE). Extraction parameters were optimized using response surface methodology to maximize the yield of total phenolic content (TPC) and total flavonoid content (TFC). The optimized extracts from UAE and EAE were then compared with conventional solvent extraction for their TPC, TFC, antioxidant activity and phenolic composition. The best optimized conditions for UAE was obtained at 33.12 min extraction time, 71.11% amplitude and a solvent-solid (SS) ratio of 39.63 mL/g. The optimized parameters for EAE were 4.81 h extraction time, 0.9% enzyme concentration and 40 mL/g SS ratio. Similar values of experimental and predicted TPC and TFC at optimized conditions indicates the suitability of the quadratic model in optimizing the extraction parameters. Further characterization of extracts suggested EAE as most efficient process in extracting bioactive compounds.
Keywords: Antioxidant activity; Citrus paradisi; Conventional and non-conventional extraction; Enzyme/ultrasound extraction; Phenolics; Response surface methodology.