A selective extraction of hydroxytyrosol rich olive oil from alperujo

Alperujo, the solid-liquid waste generated by the current two-phase method of olive oil extraction, was dried, milled and treated with supercritical carbon dioxide (sc-CO2) to obtain a hydroxytyrosol (HT)-rich oil. At first, extraction rates were analysed as a function of operating variables and the pre-condition of the raw material. Samples with particle size diameter < 0.80 mm and in equilibrium moisture (1%) with the atmosphere, improved oil extraction yield almost 40% compared with samples with the whole range of particle sizes. Extraction yield improved with solvent flow rate, but a minimum residence time was required. The optimum was 0.18 kg h(-1) (7.5 kg CO2 h(-1) kg biomass(-1)). Higher pressures and lower temperatures resulted in higher extraction yields; at 30 MPa and 323 K the extraction curve slope was close to the theoretical oil solubility and the yield was 13%, like that obtained with n-hexane by Soxhlet (14%). However, the HPLC-DAD analysis identified higher HT concentration (1900 ppm) in the supercritical extracts at the highest temperature. Consequently, at 373 K, the total phenol content and the antioxidant capacity of the extracts was uppermost. No HT was found in the n-hexane extracts.