Olive cake, the most important byproduct of olive oil extraction by the two-phase centrifugation system, was used to obtain phenolic extracts. The extracts were obtained using the two constituents of this waste, vegetative water and solid residue, to maximize the extraction of all phenolic compounds. Different extraction procedures were studied, a simple and rapid extraction procedure being developed from the solid residue using an accelerated solvent extractor (ASE). Afterward, the phenolic extracts were fractionated using semipreparative HPLC to study the antioxidant activity of the different components. The identification of the phenolic compounds was carried out with an ultraperformance liquid chromatograph coupled to tandem mass spectrometry equipment (UPLC-ESI-MS/MS). With this method, a complete list of the polyphenols from the extract was obtained. Finally, the antioxidant activity of the phenolic extracts and the isolated fractions was evaluated, showing great antioxidant capacities, between 3450 and 17900 micromol of Trolox equivalents/g of extract. With regard to the isolated fractions the most antioxidant were those that contained hydroxytyrosol and 3,4-DHPEA-EDA. The suitability of the solid residue extract obtained by the ASE procedure was demonstrated given the great range of phenolic compounds and the feasibility of production on an industrial scale.

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Phenolic compounds are one of the main reasons behind the healthy properties of virgin olive oil (VOO). However, their daily intake from VOO is low compared with that obtained from other phenolic sources. Therefore, the intake of VOO enriched with its own phenolic compounds could be of interest to increase the daily dose of these beneficial compounds. To evaluate the effectiveness of enrichment on their bioavailability, the concentration of phenolic compounds and their metabolites in human plasma (0, 60, 120, 240 and 300 min) from thirteen healthy volunteers (seven men and six women, aged 25 and 69 years) was determined after the ingestion of a single dose (30 ml) of either enriched virgin olive oil (EVOO) (961·17 mg/kg oil) or control VOO (288·89 mg/kg oil) in a cross-over study. Compared with VOO, EVOO increased plasma concentration of the phenol metabolites, particularly hydroxytyrosol sulphate and vanillin sulphate (P,0·05). After the consumption of VOO, the maximum concentration of these peaks was reached at 60 min, while EVOO shifted this maximum to 120 min. Despite these differences, the wide variability of results indicates that the absorption and metabolism of olive oil phenols are highly dependent on the individual.

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