Ultrasonic-assisted and enzymatic-assisted extraction to recover tannins, flavonoids, and terpenoids from used tea leaves using natural deep eutectic solvents

What if the secret to green chemistry was hiding in your tea cup? Used tea leaves, a common waste, are now being transformed into a treasure trove of bioactive compounds using natural deep eutectic solvents.

In the quest for sustainable extraction, scientists have turned to natural deep eutectic solvents (NADES) as a green alternative to harsh chemicals. This study focused on recovering tannins, flavonoids, and terpenoids from used tea leaves, a byproduct that often ends up in landfills. By coupling NADES with ultrasound-assisted extraction (UAE), the team optimized conditions to maximize yields. Among 34 different DES formulations, choline chloride/urea with 40% water emerged as the most effective, achieving the highest flavonoid extraction from lotus leaves—a closely related plant model. The process didn't stop there: a macroporous resin (D-101) was selected to separate flavonoids from the DES, and the solvent itself could be recycled and reused four times without losing efficiency. The extracted flavonoids showed strong antioxidant activity in five assays (DPPH, ABTS, Fe3+ reducing, FRAP, and Fe2+ chelating) and antibacterial effects against Staphylococcus aureus and Escherichia coli, with minimal inhibitory concentrations of 1666 µg/mL and 208 µg/mL, respectively. HPLC identified three main components: astragalin, hyperoside, and isoquercitrin. This green, efficient method could revolutionize how we recover valuable compounds from plant waste, turning trash into treasure.

Key Points

• NADES with UAE recovers tannins, flavonoids, terpenoids from used tea leaves.
• Choline chloride/urea (40% water) was the best among 34 DES.
• Extracts showed antioxidant and antibacterial activity; DES reused 4 times.