## Materials and Methods
### Extraction of Phenolic Compounds from Olive Leaves by Microwave-Assisted Extraction (MAE)  
MAE extraction was carried out in a microwave extraction reactor (Anton Paar GmbH, Graz, Austria) equipped with two standard magnetrons of 850 W that deliver up to 1500 W microwave power and an autosampler (model MAS 24). Extracts were prepared according to [PERSON] et al. by adding 3 g of dried olive leaf powder into a closed extraction vessel with 30 mL of ethanol/water solvent mixture [23]. The solvent was selected because ethanol is generally recognized as a safe solvent to use in food products [24]. Extraction time, temperature and percentage of ethanol were varied according to the experimental design. After cooling, samples were centrifuged at 13,000 rpm for 15 min at 4 \({}^{\circ}\)C in a centrifuge (Sorvall ST 16 R, Thermo Scientific, Leicestershire, UK) and the supernatant was collected and evaporated at 35 \({}^{\circ}\)C to dryness in a Savan SC250 EXP Speed-Vac (Thermo Scientific, Leicestershire, UK). The extract was stored at \(-\)18 \({}^{\circ}\)C until further use. Characterization of MAE Olive Leaf Extract by High-Performance Liquid Chromatography Coupled to Electrospray Ionization Time-of-Flight Mass Spectrometry (HPLC-ESI-TOF-MS)  
According to previous studies, dried olive leaf extracts obtained by MAE were reconstituted in the proportion of 1/4 m/v (0.25 mg/mL) of MeOH/H\({}_{2}\)O (50/50) and the extracts were filtered prior to analysis with single-use syringe filters (0.20 \(\upmu\)m pore size) and then injected into the HPLC system [25,26]. Analyses of the phenolic compounds of olive leaves were carried out following the previously validated method of [PERSON] et al. [26] using Agilent 1200 Series Rapid Resolution liquid chromatography system (Agilent Technologies, CA, USA), which is comprised of a binary pump, degasser, and auto sampler. Phenolic compounds were separated using a Poroshell 120 EC-C18 (4.6 \(\times\) 100 mm, 2.7 mm) from Agilent Technologies, at 25 \({}^{\circ}\)C and a flow rate of 0.8 mL min\({}^{-1}\). The mobile phases were 1% of acetic acid as mobile phase A and acetonitrile as mobile phase B. The conditions of the solvent gradient were as follows: 0 min, 5% B; 4 min, 9% B; 7 min, 12% B; 8 min, 15% B; 9 min, 16% B; 14 min, 20% B; 15 min, 22% B; 18 min, 28% B; 19 min, 30% B; 20 min, 31% B; 21.50 min, 32% B; 23 min, 34% B; 24 min, 35% B; 25.5 min, 40% B; 27 min, 50% B; 30 min, 100% B; 34 min, 100% B; 36 min, 5% B. In addition, the HPLC system was coupled to a microTOF(Bruker Daltonics, Bremen, Germany), an orthogonal-accelerated TOF mass spectrometer, using an electrospray interface (model G1607A from Agilent Technologies, Palo Alto, CA, USA). The effluent from the HPLC column was split using a T-type phase separator before being introduced into the mass spectrometer (split ratio = 1:3). Analysis parameters were arranged using a negative-ion mode with a scan range from m/z 50 to 1000. The optimum values for the ESI-MS parameters were as follows: capillary voltage, +4.0 kV; drying gas temperature, 200 \({}^{\circ}\)C; drying gas flow, 9.0 L min\({}^{-1}\); and nebulizing gas pressure, 2.0 bar. The data was processed using the software Data Analysis 4.0 (Bruker Daltonik, Bremen, Germany). The identified compounds were carried out by the generation of the candidate formula with a tolerance of 10 ppm (part per million mass error) using the SmartFormula(tm) editor and considering their retention time (RT), mass spectrum and the information available in the literature. The integration of peak areas of compounds were carried out using Bruker Compass Target Analysis 1.2 software for compound screening (Bruker Daltonics, Bremen, Germany). Three standard calibration graphs were prepared for quantification of the compounds in the olive leaves using three standards (hydroxytrosol, oleuropein and apigenin). Response Surface Methodology for Evaluation of MAE Parameters on Concentration of Compounds in Olive Leaves  
The evaluation was carried out using a Box-Behnken design with 3 variables.