Valorization of Olive Leaf Polyphenols by Green Extraction and Selective Adsorption on Biochar Derived from Grapevine Pruning Residues

What if the secret to sustainable agriculture lies in turning waste into a treasure chest of health-boosting compounds? A new study shows how grapevine prunings can selectively capture valuable polyphenols from olive leaves.

In an era of intensive farming, waste is inevitable—but it doesn't have to be wasted. Researchers are turning agricultural leftovers into high-value products, and this study is a prime example. They used biochar, a charcoal-like material made from grapevine pruning residues, as a sponge to soak up specific polyphenols from olive leaf extracts. These compounds, abundant in olive leaves, are prized for their antioxidant properties and industrial potential.

The extraction process was green from the start, using water as the only solvent. The team compared three methods—maceration, ultrasound, and microwave—at different temperatures and solid-to-liquid ratios. The biochar's adsorption behavior was best described by the Freundlich isotherm model, suggesting a heterogeneous surface with multilayer adsorption. Oleuropein, the most abundant polyphenol, showed the strongest affinity, with a Kf value of 20.4 (mg/g) × (L/g)^n and an R² of 0.9715.

Optimal conditions varied: a moderate dose of 0.5 g biochar worked best for most compounds, but oleuropein and hydroxytyrosol required a higher dose of 2.5 g. This selective uptake highlights biochar's potential as a targeted adsorbent. The study concludes that grapevine-derived biochar is a promising, eco-friendly tool for recovering high-value phytochemicals, turning waste into opportunity.

Key Points

• Biochar from grapevine prunings adsorbs olive leaf polyphenols selectively.
• Freundlich model best describes adsorption; oleuropein had highest Kf (20.4).
• Optimal biochar dose varies: 0.5 g for most, 2.5 g for oleuropein/hydroxytyrosol.