*2.1. Plant Material, Supercritical CO2 Extraction and Chemical Characterization*

Olive leaves from the El Hor olive variety cultivated in Kairouan (center of Tunisia) were collected in January 2018 (voucher code OE00182). The cultivar was identified by Pr. Mokhtar Zarrouk. Dried leaves were kept under shade at 25 ◦C and fresh leaves were ground using an Ultra Centrifugal Mill ZM 200 (RetschGmbh, Haan, Germany). Extraction of phytochemicals was carried out according to a previously reported method [37]. Briefly, 10 g of ground leaves were homogenized with sea sand in a ratio 1:1.5 (m/m), loaded onto the extraction vessel, packed with glass wool and pressurized until working conditions. Extractions were carried out at 150 bar and 40 ◦C using a mixture of CO2 and ethanol (6.6%) as the extraction solvent which passed through the extraction cell for one hour at 23 g/min. The obtained extract was finally collected and the solvent was evaporated under vacuum at 38 ◦C. The extraction yields were 9.3% and 16.7% for fresh and dried leaves, respectively.

Olive leaf extracts were analyzed for their phenolic and triterpenoids composition by high performance liquid chromatography coupled to electrospray ionization and time of flight mass spectrometry (HPLC-ESI-TOF/MS). To achieve this goal, SFE extracts were reconstituted in an extraction co-solvent up to a concentration of 5000 mg/L and filtered through a 0.2 μm polytetrafluoroethylene (PTFE) syringe filter prior to further analysis. Qualitative and quantitative determination of both phenolic compounds and terpenoids were carried out according to the previously reported method [38]. Quantitation was carried out using available commercial standards of six phenolics and two terpenoids: hydroxytyrosol, vanillin, luteolin, ferulic acid, (+)-pinoresinol, oleuropein, oleanolic, and maslinic acids. These standards were purchased from Sigma–Aldrich (St. Louis, MO, USA), Arbo Nova (Turku, Finland), and Extrasynthèse (Lyon, France). The stock solutions containing these analytes were prepared by dissolving the appropriate amount in methanol or methanol/water (50/50, *v*/*v*) at a concentration level of 1 mg/L. All calibration curves showed good linearity over the range of study with a minimum value of R2 = 0.994.
