Development of a green extraction procedure with super/subcritical fluids to produce extracts enriched in oleuropein from olive leaves

The extraction of olive leaves was examined by means of selective and environmentally friendly technologies using solvents in super/subcritical state. The goal was to apply different, yet complementary techniques, based on the fractionation of the extract and its enrichment in oleuropein. The leaves were extracted with supercritical fluid extraction (SFE) and pressurized liquid extraction (PLE). Non-toxic solvents were used, namely CO2, water and ethanol. The effect of the techniques was studied upon the extracts’ yield, oleuropein content and scavenging radical activity. The serial combination of SC-CO2 modified by 5% ethanol and subcritical water afforded high extract yield (44.1%), high recovery of oleuropein (4.6%) and good antioxidant activity. It was suggested that the removal of non-polar compounds with SC-CO2 resulted in the enrichment of the residue in oleuropein, which was then extracted with PLE by subcritical water. The proposed approach provides the base for the establishment of a productive “green” extraction.