Natural Antioxidant Composition as Correlated to Stability of Some Tunisian Virgin Olive Oils

The amount and composition of tocopherols and phenols two of the main natural antioxidants in virgin olive oil have been studied in seven varieties of Tunisian olive oil. Results showed that phenol and tocopherol amounts vary according to cultivars. Among the studied varieties, the oil of Chetoui presents the highest amounts of total phenols (925.7 ± 24.3 mg/kg and tocopherols (490.7 ± 2.2 mg/kg). The prevalent phenols in studied oils were secoiridoids such as dialdehydic form of oleuropein aglycon (DFOA), dialdehydic form of ligstroside aglycon (DFLA), aldehydic form of oleumpein aglycon (AFOA), and aldehydic form of Iigstmside agiycon (AFLA). Moreover, phenoiic acids. mainly p-ooumaric acid, are well represented. Flavonoids (apigenin and luteolin) and lignans (pinoresinol and acetoxypinoresinol) were also detected in our samples. As reported by some authors, total phenols, o-diphenols, secoiridoids and hydroxytyrosol amounts show a good correlation with stability measured by Rancimat. There is a lower influence of tocopherols and lignaiis, Nevertheless, the stability of Sayali oil seems due to its high oleic/linoleic ratio rather than to its phenol content.