Introduction: Hydroxytyrosol is a powerful natural antioxidant contained in olive oil and its by-products. Among them, olive oil dregs (OOD), an underexploited semi-solid residue that precipitates in unfiltered olive oils, contain significant amounts of hydroxytyrosol. The purpose of this work was the enrichment of the polyphenolic component, in particular hydroxytyrosol, in OOD extract through liquid chromatography on Amberlite XAD7HP and XAD16N resins. Material & Methods: An OOD aqueous extract was prepared , and Amberlite XAD16N and XAD7HP were used for the recovery of hydroxytyrosol. Different elution conditions were tested. Polyphenols were estimated by Folin-Ciocalteu. Hydroxytyrosol was quantified by RP-HPLC. Antioxidant activities were assessed in the pool containing the highest quantity of hydroxytyrosol. Results: Total Phenolic Content and hydroxytyrosol in the OOD extract were 6.24±0.10 mg Gallic Acid Equivalents/g and 532.98±5.78 ug/g, respectively. Elution with 25% ethanol provided the highest hydroxytyrosol recovery (92.50% from XAD7HP). Ferric Reducing Antioxidant Power of hydroxytyrosol-enriched preparation was comparable to the OOD extract, while Radical Scavenging Activity was higher for the preparation (92.83%±0.44 and 44.12%±1.82, respectively). Conclusion: The results demonstrate that hydroxytyrosol can be recovered with high yield from OOD, providing a preparation with high radical scavenging power. Moreover, it is proved that this by-product can be usefully exploited.

Hydroxytyrosol (HT) is one of the most powerful natural antioxidants, mainly contained in olive oil and its by-products. Here, a procedure for the preparation of an HT-enriched sample is described. An acidic aqueous extract (pH 1.25) from Olive Oil Dregs (OOD), a by-product from oil mills, was prepared by incubation at 37 °C for 1 h. The total phenolic content and HT amount were 6.24 +/- 0.10 mg gallic acid equivalent/g OOD and 532.98 +/- 5.78 ug/g OOD, respectively. Amberlite XAD16N and XAD7HP resins were used for the recovery of HT from the raw extract. Several elution conditions were tested with both resins, and elution with 25% ethanol provided the highest HT recovery (92.50% from XAD7HP). Antioxidant activities were assessed in the pool containing the highest quantity of HT. The results were compared with those of the raw extract. Ferric reducing antioxidant power values were comparable (95.71 +/- 2.50 and 96.64 +/- 13.47 ug ascorbic acid equivalent/mg for HT-enriched pool and raw extract, respectively), while the radical scavenging activity was higher for the pool (92.83% +/- 0.44 and 44.12% +/- 1.82, respectively). The results reported here demonstrate that HT can be recovered with a high yield from OOD, providing a preparation with high radical scavenging power. In addition, it is proved that this by-product, poorly considered up to now, can be usefully exploited.

Olive oil dregs (OOD), which are an underutilized by-product from oil mills, were used for the extraction of antioxidant compounds. The residues from three oil mills located in Campania (Southern Italy) were extracted with acidified methanol, and hydroxytyrosol (HT) was the main phenolic compound detected. Total phenolic content (TPC) and HT amount were measured. EVO Campania oil mill provided the residue with the highest TPC and HT quantities: 6.801 ± 0.159 mg Gallic Acid Equivalents (GAE)/g OOD and 519.865 ± 9.082 µg/g OOD, respectively. Eco-friendly extractions at different temperatures and times were performed on EVO Campania OOD, obtaining 9.122 ± 0.104 mg GAE/g OOD and 541.330 ± 64.087 µg/g OOD for TPC and HT, respectively, at 121C for 60 min. Radical Scavenging Activity (RSA), Superoxide Scavenging Activity (SSA), and Ferric Reducing Antioxidant Power (FRAP) were measured in OOD aqueous extracts. Extract prepared at 37C for 60 min showed the greatest RSA and SSA values (44.12 ± 1.82 and 75.72 ± 1.78, respectively), whereas extract prepared at 121C for 60 min exhibited the highest FRAP value (129.10 ± 10.49 µg Ascorbic Acid Equivalents (AAE)/mg). OOD extracts were able to protect sunflower oil from oxidation for 4 weeks at 65C. The overall results suggest that this novel residue can be usefully valorized by providing HT-rich extracts to use as antioxidant agents.