Comparison among Different Green Extraction Methods of Polyphenolic Compounds from Exhausted Olive Oil Pomace and the Bioactivity of the Extracts

What if the leftover olive pomace, already stripped of its oil, still holds a treasure trove of health-boosting compounds? A new study shows that green extraction methods can unlock these hidden gems—and even fight bacteria.

In the quest for a circular economy, waste is the new gold. The olive oil industry produces mountains of olive pomace—and after the last drops of oil are extracted with hexane, what's left is often discarded. But this 'exhausted' pomace still contains bioactive polyphenols, waiting to be rescued.

Scientists tested several green extraction methods: simple solvents (water or hydroalcoholic mixtures), ultrasound, Ultra-Turrax (a high-speed blender), and enzymes (cellulase or viscoenzyme). They measured the phenolic profile, total phenolic content, and antioxidant activity of each extract.

Results were striking. Enzyme-assisted extraction, with or without ultrasound, gave the highest yields. But the ultrasound-assisted hydroethanolic extraction (USAHE) produced the most abundant identified phenolics: 2.021 mg hydroxytyrosol, 0.987 mg tyrosol, and 0.121 mg catechol per 100 mg extract. Meanwhile, plain water at 50°C achieved the best total phenolic content and antioxidant activity.

And here's the bonus: USAHE extracts inhibited Gram-positive bacteria, especially Bacillus cereus, with 67.2% inhibition at a 3% extract concentration. So, the 'waste' from olive oil might just be a source of natural preservatives and health compounds.

Key Points

• Enzyme-assisted extraction gave highest yields, with or without ultrasound.
• USAHE yielded most phenolics: hydroxytyrosol, tyrosol, catechol.
• USAHE inhibited Bacillus cereus by 67.2% at 3% extract.