Optimization of ultrasound-assisted extraction of bioactive properties from date palm (Phoenix dactylifera L.) spikelets using response surface methodology

Response surface methodology (RSM) was applied to optimize the experimental conditions for ultrasound-assisted extraction (UAE) to maximize the recovery of total phenolic content (TFC) and 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical scavenging activity from date palm spikelets (DPS). A three-factor [temperature (25 °C, 42.5 °C, and 60 °C), duration (20, 30, and 40 min), and ethanol concentration (25%, 37.5%, and 50%)] and three-level (−1, 0, and +1) Box–Behnken design (BBD) was applied. Sonication temperature and ethanol concentration were the major factors influencing the recovery of total phenolic content (TPC) and DPPH radical scavenging activity from DPS. The experimental values [TPC, 130.2 mg gallic acid equivalents (mg GAE/g), and DPPH radical scavenging activity, 87.5%] well matched with the predicted values (TPC, 124.5 mg GAE/g, and DPPH radical scavenging activity, 87.2%) at the optimum UAE conditions (temperature 40.8 °C, duration 21.6 min, and ethanol concentration 50.0%), which confirmed the validity of the applied RSM model. The major phenolic compounds in DPS determined at optimized UAE conditions were rutin and (+)-catechin. This study identified the ideal UAE settings for the maximum recovery of bioactive compounds from DPS for possible utilization of date byproducts in food applications.