Phenolic composition and in vitro antioxidant capacity of four commercial phytochemical products: Olive leaf extract (Olea europaea L.), lutein, sesamol and ellagic acid

Four commercially available natural products (olive leaf extract, lutein, sesamol and ellagic acid) were investigated for in vitro antioxidant properties using the DPPH, ABTS+, ferric reducing antioxidant capacity (FRAP), oxygen reducing antioxidant capacity (ORAC) and β-carotene-linoleic acid assays. Antioxidant potency followed the order: ellagic acid > sesamol > olive leaf extract > lutein for all antioxidant test methods. Total phenolic content of olive leaf extract was estimated as 1.60 mg gallic acid equivalents (GAE)/g dry weight of olive leaf extract using the Folin–Ciocalteu method. Qualitative and quantitative compositional analysis carried out using high performance liquid chromatography (HPLC) coupled with photo diode array detection (DAD) revealed six major polyphenolic compounds present in olive leaf extract: oleuropein, verbascoside, luteolin-7-O-glucoside, apigenin-7-O-glucoside, hydroxytyrosol and tyrosol. Lutein, sesamol, ellagic acid and olive leaf extract all showed great potential as natural antioxidants which would be useful in the prevention of diseases in which free radicals are implicated.