Phenolic Composition and Antioxidant Activity of Monovarietal and Commercial Portuguese Olive Oils

Olive oil composition has been investigated using chemical approaches, since the composition has a direct impact on its quality and safety and it may be used for certification purposes. In this paper, eleven monovarietal and twelve commercial Portuguese olive oils were analyzed to determine spectrophotometrically their total polyphenol content, ortho-diphenols and antioxidant activity. The phenolic profiles of these olive oils were also studied by high performance liquid chromatography. The lowest phenolic content and antioxidant activity were observed for monovarietal olive oils, however, among these group, ‘Cobrançosa’ and ‘Redondil’ cultivars showed the highest values of these two chemical parameters. In commercial olive oils, the concentration of polyphenols, determined according to the Folin–Ciocalteu method, and the antioxidant activity (ABTS method) ranged from 97.37 ± 1.10 to 219.7 ± 1.50 mg GAE/kg of oil and from 387.2 ± 20.00 to 997.5 ± 30.90 µmol Trolox/kg, respectively. The study of the phenolic profile demonstrated that the highest concentrations of the most abundant compounds in olive oil (tyrosol, hydroxytyrosol and oleuropein) are present in commercial olive oils. The correlation coefficient between total phenolics and antioxidant activity was statistically significant (r = 0.95, p < 0.0001). The same was observed for ortho-diphenol content and antioxidant capacity (r = 0.94, p < 0.0001).