Evaluation and optimization of microwave‐assisted extraction of bioactive compounds from eggplant peel by‐product

A three‐level five‐factor central composite design was used for microwave‐assisted extraction of bioactive compounds from eggplant peel. The extraction yields, total phenolic content (TPC), total flavonoid content (TFC), total anthocyanin content (TAC), and DPPH radical scavenging activity, reported as IC₅₀, were optimized by changing the microwave power, extraction time, liquid–solid ratio, ethanol concentration, and pH of solvent. The extraction yield, TAC, TPC, and TFC significantly increased (p < .01) parallel to the increase in microwave power and the use of lower ethanol concentrations and lower liquid–solid ratios. The maximum predicted extraction yield (3.27%), TPC (1,049.84 µg GAE/ml), TFC (130.40 µg QE/ml), and TAC (6.99 mg/L) and the minimum predicted IC50 (0.52 ml/mg) were simultaneously obtained when power, extraction time, liquid–solid ratio, ethanol concentration, and pH of solvent were 269.82 W, 7.98 min, 5.01 ml/g, 73.49%, and 3.06%, respectively. Overall, bioactive compounds could be effectively extracted from eggplant peels via optimized microwave conditions. PRACTICAL APPLICATIONS: The processing of eggplants by industries inevitably generates large amounts of peel as food waste. This valuable by‐product comprises anthocyanins that are a type of polyphenol with potential applications as natural food colorant and antioxidant. In this research, microwave‐assisted extraction (MAE) was performed as an effective method for the extraction of anthocyanins and phenolic and flavonoid compounds from eggplant peel. Afterward, the yield of the mentioned bioactive compounds derived from eggplant peel extracts was optimized through managing several MAE parameters such as microwave power, extraction time, liquid–solid ratio, ethanol concentration, and pH of the solvent. Such new information concerning the recovery of these valuable components from waste can improve the economy for canning industries and minimize the potential pollution of these wastes.