Methods for preparing phenolic extracts from olive cake for potential application as food antioxidants

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.