Ethanol-based ultrasound-assisted extraction for the sustainable recovery of major flavanone glycosides from mandarin peel.

Mandarin peel (MP), a major citrus-processing by-product, contains flavanone glycosides with antioxidant potential, yet its effective valorization depends on the development of a safe, efficient, and scalable extraction process. In this study, an ethanol-based ultrasound-assisted extraction (UAE) process was developed for the simultaneous recovery of hesperidin, narirutin, and didymin from MP. Response surface methodology based on a central composite design was applied to evaluate the effects of ethanol concentration, temperature, solid loading, and ultrasound amplitude on flavonoid recovery. The developed regression models showed good predictive reliability, with R2 values of 0.9321, 0.8996, and 0.9296 for hesperidin, narirutin, and didymin, respectively. The optimal conditions were determined to be 78.22 % ethanol, 68.12 °C, 64.31 g/L solid loading, and 28.16 % amplitude for 10 min. Under these conditions, the experimental recoveries of hesperidin, narirutin, and didymin were 36.15, 17.97, and 2.35 mg/g-biomass, respectively, which agreed with the predicted values by more than 90 %. The resulting MP extract contained 23.41 % total flavonoids and exhibited ABTS radical scavenging activity with an EC50 value of 384 µg/mL. No cytotoxicity was observed in L929 cells at concentrations up to 1600 µg/mL, which was more than 4-fold higher than the EC50 value. These findings indicate that ethanol-based UAE enables the rapid and simultaneous recovery of antioxidant flavonoids from MP using a generally recognized as safe solvent. This process provides a practical strategy for the sustainable valorization of mandarin peel as a natural antioxidant ingredient.