Efficient Extraction of Flavonoids from Lotus Leaves by Ultrasonic-Assisted Deep Eutectic Solvent Extraction and Its Evaluation on Antioxidant Activities

What if the secret to greener chemistry lies in a simple mix of choline and urea? Scientists just used this unlikely duo to unlock flavonoids from lotus leaves—efficiently, sustainably, and with impressive antioxidant power.

Lotus leaves are more than just pond decor—they're packed with flavonoids, natural compounds with antioxidant and antibacterial potential. But extracting them usually involves harsh solvents. Now, researchers have turned to deep eutectic solvents (DES), a greener alternative, paired with ultrasound assistance to make the process faster and more efficient. After screening 34 different DES, they found the winning formula: choline chloride and urea with 40% water, which maximized flavonoid yield from the leaves. To purify the extract, they used a macroporous resin called D-101, and the DES itself could be recycled and reused up to four times without losing effectiveness—a win for both science and the environment. The extracted flavonoids showed antioxidant activity across five different assays (DPPH, ABTS, Fe³⁺ reducing, FRAP, and Fe²⁺ chelating) and also inhibited the growth of Staphylococcus aureus and Escherichia coli, with minimal inhibitory concentrations of 1666 µg/mL and 208 µg/mL, respectively. HPLC analysis identified three main components: astragalin, hyperoside, and isoquercitrin. This eco-friendly method could transform how we harvest valuable compounds from nature.

Key Points

• Choline chloride/urea with 40% water is the best DES for flavonoids.
• DES can be recycled and reused four times effectively.
• Extract shows antioxidant and antibacterial activity against two strains.