Toward a high yield recovery of antioxidants and purified hydroxytyrosol from olive mill wastewaters.

We investigated to develop effective procedures to recover the potentially high-added-value phenolic compounds contained in the discontinuous three-phase olive processing wastewaters (OMW). Particular emphasis was made to extract and purify hydroxytyrosol, one of the major compounds occurring in OMW. Batch optimization experiments showed that ethyl acetate is the most efficient solvent for the recovery of phenolic monomers from OMW. The latter was used with an optimal pH equal to 2. Furthermore, the percentage of each monomer, and particularly hydroxytyrosol, in the extract was maximum for a solvent ratio and a theoretical extraction stage number equal to 2 and 3, respectively. High yield (85.46%) recovery of hydroxytyrosol was achieved from OMW using a three-staged continuous counter-current liquid-liquid extraction unit. Hydroxytyrosol (1.225 g) were extracted per liter of OMW. One gram of hydroxytyrosol per liter of OMW was then purified by means of a chromatographic system which could be adapted to a large scale production process.