Two-Step Optimization of Processing Conditions to Extract Bioactive Compounds from Eggplant Peels

Optimization of processing conditions to extract bioactive compounds from plant sources has attracted great attention due to their high potential applications. In this study, Plackett-Burman design (PBD) was used for screening to select three significant factors among seven factors including ethanol content, extraction duration, solvent/solid ratio, extraction temperature, pH, and drying temperature for the ultrasound-assisted extraction of bioactive compounds from eggplant (Solanum melongena) peels. Subsequently, Box-Behnken design (BBD) was used to determine the optimal levels of the three significant factors to maximize the total phenolic content (TPC), anthocyanin content (AnCo) and antioxidant activity (AnAc) of the extract. The optimized conditions included the drying temperature of 53oC, ethanol content of 78% and the solvent/solid ratio of 44 mL/g, leading to the predicted optimal values for the TPC of 21.98 mg gallic acid equivalent (GAE)/g dry weight (DW), AnCo of 0.67 mg cyanidin-3-glucoside equivalent (CGE)/g DW and AnAc of 27.04 mg Trolox equivalent (TE)/g DW. In the validation, these values were 21.43±0.62 mg GAE/g DW, 0.64±0.02 mg CGE/g DW, and 25.51±0.38 mg TE/g DW, respectively, close with their predicted ones, confirming the adequacy of the models. In conclusion, eggplant peels could be a good source of bioactive compounds, and the combination of PBD and BBD could be effectively employed in screening and optimization for various extraction techniques.