Tunisian Wild Olive Leaves: Phenolic Compounds and Antioxidant Activity as an Important Step Toward Their Valorization

Olive leaves are one of the most prevalent by-products of the olive oil industry and may be exploited as a low-cost source of high-added-value phenolic compounds. The pharmaceutical, cosmetic, and food sectors are becoming more interested in the therapeutic effects attributed to these bioactive components in olive leaf extract. This work offers some indication of the chemical potentialities of oleasters leaf as a new source of functional food. Qualitative and quantitative compositional analysis revealed 14 major phenolic compounds among which oleuropein, hydroxytyrosol, apigenin 7-O-glucoside, tyrosol, epicatechin, and vanillic acid were identified. The bioactive compounds that presented the least concentration were gallic, vanillic, p-coumaric, and chlorogenic acids. Maximum concentrations were found for hydroxytyrosol, oleuropein, and luteolin-7-o-glucoside in wild olive leaves. Concerning the antioxidant activity, the oleaster leaves showed high antioxidant proprieties using ABTS (acide 2,2’-azino-bis-(3-éthylbenzothiazoline6-sulfonique) method. Chemometrics (principal component analysis (PCA) and dendrogram analysis) were applied to the quantitative phenolic compounds data, allowing good discrimination of the phenols according to their antioxidant activities. The oleaster leaves seem to be a source of antioxidants and can be an attractive tool for industrial uses.