Pretreatment of Olive Mill Wastes for the Extraction of Residual Oil and High Added Value Compounds

A novel extraction method for recovering the residual oil from olive mill wastes (OMW) from II-phase olive mills was developed in this study. The new acidification/hydrolysis method is based on the addition of sulphuric acid and ferrous sulphate heptahydrate. A range of water dilutions and extraction temperatures were tested. Experimental runs were carried out according to a central composite design taking into consideration all the most important factors that affect the extraction process such as the solid to liquid ratio (w/v), the addition of H 2 SO 4 (% v/w), the addition of FeSO 4 ·7H 2 O (% w/w) and temperature (°C). The optimum residual oil yield was 47.7 mg/g OMW dry basis (db) at 0.25 w/v solid to liquid ratio, 1.4% v/w H 2 SO 4 , 0.6% w/w FeSO 4 ·7H 2 O and 70 °C. Moreover, the extraction kinetics of the residual oil from OMW were examined at the optimum conditions and were well fitted by using second order kinetics. Analysis of the residual oil showed similar fatty acid profile with the virgin olive oil. Finally, characterisation of the aqueous phase following the residual oil extraction process demonstrated a high content of phenolic compounds and especially tyrosol and hydroxytyrosol. Graphic Abstract