Deep Eutectic Solvents and Wall-Breaking Technique: A New Frontier in the Extraction of Oleuropein and Flavonoids from Olive Leaves with Superior Antioxidant and Antitumor Potential

What if the key to unlocking nature's most powerful antioxidants lies in a green solvent and a burst of mechanical force? A new study shows how olive leaves, a byproduct, can be transformed into a treasure trove of bioactive compounds.

Olive leaves are often discarded, but they hide a potent secret: oleuropein and flavonoids, compounds with remarkable health benefits. Yet, extracting them efficiently has been a challenge. This study introduces a game-changing duo: a deep eutectic solvent (DES) made from choline chloride and ethylene glycol, combined with wall-breaking extraction (WBE), a technique that uses mechanical force to crack open plant cells. The DES outperformed traditional solvents like lactic acid and methanol, especially with a 30% moisture content. Using response surface methodology, the team optimized conditions: 30% moisture, 140 seconds of wall-breaking, and a liquid-solid ratio of 230 mL/g. This yielded impressive amounts: 88.87 mg/g of oleuropein, 4.57 mg/g of luteolin-7-O-glucoside, and 114.31 mg RE/g of total flavonoids from dry matter. Among three olive varieties, young Picholine leaves stood out with the highest concentrations. The Picholine extract showed strong antioxidant activity (ABTS•+ 155.10 mg/mL, DPPH• 44.58 mg/mL) and, in CCK-8 assays, significantly inhibited the growth of Eca-109 human esophageal cancer cells at 25 µg/mL for 24 hours, while sparing normal Het-1A cells. This green process not only valorizes agricultural waste but also opens doors for supplements, cosmetics, and functional foods.

Key Points

• Green DES with wall-breaking boosts olive leaf extraction.
• Picholine leaves yield highest oleuropein and flavonoids.
• Extract inhibits esophageal cancer cells in vitro.