Green chemistry strategies for Flavonol extraction from onion: Exploring natural deep eutectic solvents.  

A. González-De-Peredo, A. Maroto, A. Memboeuf, Microchemical Journal 2025, 215, 114445. DOI: 10.1016/j.microc.2025.114445  

The increasing interest in bioactive compounds from fruits and vegetables has driven the need for efficient and environmentally friendly extraction methods. Traditional solvents such as methanol or acetonitrile, although effective, pose significant environmental concerns. This study explores the use of choline chloride-based natural deep eutectic solvents (NaDES) for the extraction of flavonols from onions, compounds known for their health benefits. Various NaDES combinations (levulinic acid, tartaric acid, 1,3-propanediol, and urea) and molar ratios (1:1, 1:2, 1:3, 1:4, 2:1, 2:3) were tested. The choline chloride:levulinic acid mixture at a 1:2 ratio showed the highest extraction efficiency for five major onion flavonols: quercetin 4′-glucoside, quercetin 3-glucoside, isorhamnetin 3,4′-diglucoside, isorhamnetin 4′-glucoside, and quercetin 3,4′-diglucoside, as determined by liquid chromatography–mass spectrometry. To optimize extraction conditions, a Box-Behnken design was applied to the choline chloride:levulinic acid NaDES system, with the variables studied being water content (25–65 % v/v), extraction temperature (20–40 °C), and extraction time (2–20 min). The optimized NaDES-based method was compared with traditional extraction techniques using methanol and green solvents such as ethanol, ethanol/water, and water. The results indicated that the NaDES system yielded comparable or higher amounts of flavonols (4.83 ± 0.05 mg g−1), demonstrated good intermediate precision (RSD < 10 %), and significantly reduced the extraction time. This approach improves flavonol extraction and offers a more sustainable and environmentally friendly alternative, positioning NaDES as a promising and green method for future extraction processes.