Optimization of microwave-assisted extraction parameters and characterization of phenolic compounds in Yellow European Plums

Yellow European Plums (YEPs) are a rich source of phenolic compounds and antioxidants, which can be obtained using microwave-assisted extraction (MAE). During this study, two MAE experiments were performed to optimize MAE extraction parameters and the MAE process using YEPs. The first experiment was to determine the influence of independent variables such as solvent concentration (20, 60, and 100 %) and solid-to-solvent ratio (0.05, 0.1, and 0.15 g/mL), on the yield of total phenolic content (TPC) and antioxidant activity (1,1-diphenyl-2-picrylhydrazyl (DPPH) and ferric ion reducing antioxidant power (FRAP)), for ethanol and methanol, during MAE. Using a response surface methodology, the optimized extraction parameters for MAE were then found to be 60 % ethanol at a solid-to-solvent ratio of 0.1 g/mL. Using the optimized parameters from the first experiment, the second experiment evaluated the effect of microwave temperature (50, 60, 70 degrees C) and duration (5, 10, and 15 min) on TPC, DPPH, and FRAP, using a face-centered central composite design. Individual phenolic compounds, including ascorbic acid, neochlorogenic acid, and chlorogenic acid, were quantified using high performance liquid chromatography. In the second experiment, it was observed that time and temperature had a significant (p <= 0.05) effect on the extraction of phenolic compounds from four genotypes of YEPs. However, due to their diverse phenolic composition, there was not one optimal operating time and temperature suitable for all genotypes.