Effects of green extraction solvents on phenolic contents and bioactivities of Persicaria odorata (Lour.) Sojak

What if the secret to greener chemistry lies in a simple mix of choline and urea? Scientists just used it to unlock powerful antioxidants from lotus leaves—and it works brilliantly.

In the quest for sustainable extraction, researchers turned to deep eutectic solvents (DES)—a class of green liquids made from cheap, biodegradable components. They paired these solvents with ultrasound-assisted extraction (UAE) to pull flavonoids from lotus leaves, a plant long celebrated in traditional medicine. After screening 34 different DES formulations, a mixture of choline chloride and urea with 40% water emerged as the star performer, yielding the highest flavonoid content under optimized conditions.

But the innovation didn't stop there. To isolate the flavonoids, the team used a macroporous resin called D-101, which effectively separated the compounds from the DES. Remarkably, the solvent could be recycled and reused up to four times without losing its efficiency—a win for both cost and the environment.

The extracted flavonoids proved their worth in bioactivity tests. They showed antioxidant activity across five different assays (DPPH, ABTS, Fe³⁺ reducing, FRAP, and Fe²⁺ chelating), and displayed antibacterial effects against 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 UAE-DES method, followed by resin treatment, offers a powerful, eco-friendly route to extract and enrich flavonoids—not just from lotus leaves, but potentially from many other natural products. It's a green light for greener chemistry.

Key Points

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