Chétoui olive leaf extracts: influence of the solvent type on phenolics and antioxidant activities

The aim of this study was to investigate the influence of the solvent type on the extraction of phenolics and the antioxidant properties of the extracts obtained from Chetoui olive leaves. Extraction was conducted at room temperature using four solvents: deionized water (ddH2O), 80% methanol (80% MeOH), 70% ethanol (70% EtOH), and 80% acetone. Total phenols and total flavonoids were measured using the Folin-Ciocalteau and aluminum chloride colorimetric methods, respectively. The antioxidant properties have been determined by two scavenging activity methods, DPPH and ABTS. The total phenol and flavonoid contents of the olive leaf extracts (OLEs) ranged from 16.52 to 24.93 mg gallic acid g –1 DM and from 6.23 to 21.47 mg catechin g –1 DM, respectively. The IC50 values of DPPH varied from 0.17 to 0.97 mg mL –1 and the antioxidant activity values determined by ABTS (trolox equivalent antioxidant capacity) were between 629.87 and 1064.25 μmol TE g –1 DM. Our results revealed that extracting solvents have a significant influence on the antioxidant properties of olive leaves and that a methanol mixture is recommended for extracts with high levels of flavonoids and important antioxidant activities. Moreover, it was noticed that the trolox equivalent antioxidant capacity (TEAC) depends more on the flavonoids (r = 0.821) than on the total phenols (r = 0.399).