*2.2. Ethanolic Ultrasound-Assisted Extraction of Flavonoids from Onion Skins*

Yellow onions were purchased from a local market (Galati, Romania) in June 2020. The outer layers of onions were collected, cleaned with distilled water and dried. Before extraction, in order to obtain a homogeneous batch of particle size, the onion skins were ground to sizes smaller than 0.5 mm × 0.5 mm and used for further extraction. The flavonoidic extract was obtained by mixing 50 g of the onion skins with 450 mL of 70% ethanol solution and glacial acetic acid (ratio 9:1, *v*/*v*). The extraction was performed using a sonication bath at 40 ◦C for 30 min. In order to obtain flavonoids-enriched extracts, the extraction was repeated three times, while the supernatants were centrifuged at 5000× *g* for 10 min at 4 ◦C, collected and concentrated under reduced pressure at 40 ◦C. The obtained extract was characterized in terms of selected phytochemicals and used for microencapsulation experiments.
