There is currently a great interest on the use of the residual biomass originated from the
agricultural and food sectors as a bioresource instead as a waste, due to its high
potential for the recovery of high added-value compounds. Olive leaves, an olive oil
processing residue, contain high amounts of phenolic compounds with health-promoting
properties, such as oleuropein, tyrosol and hydroxytyrosol. These compounds can be
extracted from olive leaves to be added later in processed foods and thus increase their
healthy properties.
In this work, the recovery of phenolic compounds present in previously ground olive
leaves (size less than 1 mm) was carried out by solid-liquid extraction using several
solvents (hexane, ethanol, methanol and ethyl acetate). The olive leaves used were
kindly provided by the cooperative "Pagos de Benaval" from olive trees of the variety
"Serrana de Espadán", endemic of the Sierra de Espadán natural park (Castellón, Spain).
The total phenolic content (TPC) in extracts was determined according to the Folin-
Ciocalteau method. Olive leaf extract profile and quantitative determination of
oleuropein and hydroxytyrosol were performed in an HPLC-DAD system, and also in a
LC-MS system. The antioxidant activity of the extracts was determined by the DPPH
and ABTS assays. The best results, with a high antioxidant activity and also a high
oleuropein and hydroxytyrosol content in the extracts, were obtained when ethanol and
methanol were used as solvents. Finally, a central composite design was performed to
determine the effect of three factors (extraction temperature (25-40 ºC), solvent volumeleaf
mass ratio (5-15 mL/g) and alcohol-to-water ratio (50-90 vol. %)) on TPC,
antioxidant activity, and oleuropein and hydroxytyrosol content in the extracts, in order
to optimize the extraction process.
