Sequential extraction of hydroxytyrosol, mannitol and triterpenic acids using a green optimized procedure based on ultrasound

Olive waste is not waste—it's a treasure chest of health-boosting compounds. Now, scientists have found a green, ultrasound-powered way to unlock it in stages.

Olive-derived biomasses are packed with bioactive compounds that offer antioxidant, sweet-tasting, and health-promoting benefits. But until now, pulling them out one by one has been a challenge. A new study tackles this by using an eco-friendly method: ultrasound-assisted water extraction (UAWE). This technique applies sound waves to water, gently shaking loose valuable molecules from exhausted olive pomace (EOP)—the leftover solid after oil extraction.

The team optimized the process using a Box–Behnken design, testing amplitude, time, and solid loading. Their sweet spot: 80% amplitude, 11.5% solid loading, and 16 minutes. This yielded impressive results—total phenolic content of 40.04 mg/g, hydroxytyrosol at 6.42 mg/g, and mannitol at 50.92 mg/g. The extracts also showed strong antioxidant activity, measured by FRAP and ABTS assays. Liquid chromatography-mass spectrometry confirmed hydroxytyrosol as the star compound, with minor derivatives also identified.

After this first extraction, the remaining solid was examined. Scanning electron microscopy revealed structural changes in the pomace, and its chemical makeup was characterized for further use. Then came step two: extracting triterpenes, like maslinic and oleanolic acids, from the leftover solid. Remarkably, the ultrasound pre-treatment boosted this second extraction, even without milling the pellets. This sequential approach turns olive waste into a multi-product biorefinery, maximizing value while staying green.

Key Points

• Ultrasound-assisted water extraction optimizes antioxidant and mannitol recovery from olive pomace.
• Optimal conditions: 80% amplitude, 11.5% solid loading, 16 minutes.
• Sequential extraction also yields triterpenic acids from the residue.