Eco-friendly and high-performance extraction of flavonoids from lemon peel wastes by applying ultrasound-assisted extraction and eutectic solvents

This work aimed to develop an optimized extraction process to achieve an environmentally friendly proposal to recover flavonoids from lemon peel wastes using ultrasound-assisted extraction (UAE) and eutectic mixtures as solvents. The eutectic mixture choline chloride:acetic acid (ChCL:AA; 1:2 mol/mol) displayed the best extraction performance of the target compounds, here represented by hesperidin and narirutin. In Central Composite Rotatable Design (CCRD) approach, we identified the ideal conditions for flavonoid recovery: a solvent-to-feed ratio (R(S/F)) of 30 (v/m), 40% water content (m/m), and a static time of 40 min. Combined with a dynamic extraction time of 6 min (under cavitation), those parameters yielded optimal results in flavonoid recovery. The 320 W ultrasound power achieved the maximum yield of the target compounds (5.25 mghesperidin/gbiomass and 0.21 mgnarirutin/gbiomass). Besides, our results showed that the ChCL:AA solvent enhanced the thermal stability of flavonoids, showcasing remarkable potential as a stabilizing agent for various applications. Ultrasound-assisted extractions were superior in extraction performance compared to conventional techniques, namely maceration and magnetic stirring.