Batch stirred-tank green extraction of Salvia fruticosa mill. Polyphenols using newly designed citrate-based deep eutectic solvents and ultrasonication pretreatment

Imagine pulling the healing power of Greek sage with a solvent that's as green as the plant itself—and doing it with record-breaking energy efficiency.

Greek sage, Salvia fruticosa, is a treasure chest of polyphenols—natural antioxidants with serious health potential. But extracting them has often meant harsh chemicals and high energy. Now, scientists have designed a greener path using deep eutectic solvents (DES), a new class of eco-friendly liquids made from cheap, biodegradable components.

In this study, researchers tested a series of citrate salts paired with lactic acid or glycerol to create DES. The star performer was a mix of lactic acid and sodium citrate dibasic at a 15:1 molar ratio, dubbed LA-SCDB15. For the first time, they also uncovered a link between DES pH and extraction efficiency—a clue that could fine-tune future green extractions.

To scale up, they built a batch, stirred-tank process with an ultrasonication pretreatment. Using response surface methodology, they hit the sweet spot: 900 rpm stirring, 77% DES/water, and 15 minutes of ultrasound. This yielded a predicted maximum of 79.93 mg gallic acid equivalents per gram of dry mass—and the energy barrier was a mere 7.64 kJ mol−1, proving the process is remarkably energy-efficient.

The extracts were rich in chlorogenic acid, luteolin 7-O-glucuronide, and rosmarinic acid, outperforming other green methods. This isn't just a lab curiosity; it's a blueprint for sustainable phytochemical production.

Key Points

• LA-SCDB15 (lactic acid + sodium citrate dibasic, 15:1) is the top DES.
• Optimal: 900 rpm, 77% DES/water, 15 min ultrasound.
• Max polyphenol yield: 79.93 mg GAE/g dry mass; energy barrier 7.64 kJ/mol.