In this work, optimized techniques of conventional, ultrasound and microwave-assisted extraction were applied for the recovery of antioxidant compounds from lemon by-products (Citrus limon L). Specifically, the effect of solvent, temperature, microwave power, time and their interaction on the extraction was investigated. Among the tested solvents, the hydroalcoholic mixture (ethanol:water, 50:50) was the optimal one for all extraction techniques: in particular assisted by ultrasounds at 70 °C for 30 minutes (total phenolic content: 6.93 mg GAE g-1, total flavonoids: 2.07 mg CE g-1, ABTS assay: 18.36 µM TE g-1). Also, the other techniques allowed to obtain valuable extracts, although with relative lower amounts. The analyses of individual phenols revealed hesperidin and eriocitrin as the main compounds (respectively about 1650 and 1150 mg kg-1) after ultrasound assisted and conventional extraction. Results of this work can be useful to valorize an industrial by-product by sustainable techniques for the high-added value substances recovery.
Keywords: Antioxidant activity; UHPLC; lemon; microwave-assisted extraction; phenolic extract; ultrasound-assisted.