Recovery of antioxidant compounds from exhausted olive pomace through microwave-assisted extraction

Exhausted olive pomace (EOP) is a waste generated in large quantities each year in the olive oil industry. This biomass contains phenolic compounds with antioxidant, antiatherogenic, antiinflammatory and antimicrobial properties. For the extraction of these compounds, the use of a novel and environmentally friendly technique, microwave-assisted extraction using water as extraction solvent, was proposed. A Box-Behnken design of experiments based on the response surface methodology was used to optimise the effects of the factors temperature (70-100ºC), extraction time (4-40 min) and solids loading (2-15%). The response variables were the total phenolic content analysed by Folin-Ciocaltéau assay, hydroxytyrosol content by HPLC and antioxidant activity through FRAP and ABTS assays. The optimal conditions for each response variable were obtained. Overall, microwave-assisted extraction is considered a suitable technique for the extraction of bioactive compounds from EOP at short extraction times. In particular, the maximum content of hydroxytyrosol (6.1 mg/g of EOP) could be obtained at 99.7ºC, 3.9% (w/v) solids and 34.3 min Thereby, this extract has potential to be used as a functional and antioxidant additive.