Optimizing the microwave-assisted extraction and ultrasonic-assisted processes to acquire flavonoid and phenolic compounds from watermelon rinds using natural deep eutectic solvents

Abstract

ABSTRACTS This study extracted flavonoids and phenolics from watermelon fruit by microwave-assisted extraction (MAE) and ultrasound-assisted extraction (UAE) combined with a natural deep eutectic solvent (NADES). The effectiveness of NADES combined with UAE and MAE was evaluated for extracting these compounds from watermelon rinds. The study chose a 2:1 molar ratio of hydrogen bond donors (HBDs) to hydrogen bond acceptors (HBAs). Among the tested combinations, 1,2-propanediol-lactic acid showed the highest solubility for flavonoids and phenolics within the extraction system. Experiments with a single factor were used to examine the effects of different parameters on total phenolic content (TPC) and total flavonoid content (TFC). The Box-Behnken design (BBD) model optimized the NADES-based UAE and MAE processes based on TPC and TFC responses. The results of the experiment and the predicted values from the BBD agreed well. Optimal conditions for recovering phenolics and flavonoids from watermelon rinds with NADES-based UAE were determined as 1/60 g/ml for SLR, 300 W, 20% water content, and 15 min, while NADES-based MAE: 1/50 g/ml for SLR, 400 W, and 3 min. This study presents an efficient approach for extracting biologically active compounds from watermelon.