Biodiversity of Tunisian virgin olive oils: varietal origin classification according to their minor compounds
Résumé
The analysis of minor compounds (minor fatty acids, squalene, phenols and tocopherols) of eight autochthonous Tunisian varieties of virgin olive oils (VOOs) (Chemchali, Chemlali Sfax, Chemlali Zarzis, Chetoui, Oueslati, Sayali, Zalmati and Zarrazi) allows for the varietal origin authentication. The compositions of minor ω9 and ω7 fatty acids, especially 16:1 and 18:1 isomers, are important criteria for distinction among eight varieties of VOOs. The squalene content was ranged between 1.39 and 5.37 g/kg. Total phenol and the sum of α-, β- and γ-tocopherol contents were, respectively, ranged between 81–691 and 147–585 mg/kg. This minor fraction is not only highly dependent on the variety, but also the maturity index. Chemchali, Zarrazi and Sayali are characterized by having high content in total phenols, whereas Chemlali Sfax, Chemlali Zarzis and Zalmati are rich in total tocopherols. The intervarietal variation in the studied minor compounds was confirmed by chemometric treatment through PCAs. The potential of using the minor compounds in the authentication of the Tunisian olive oil varietal origin was tested through PLS-DA performed for the two most representative varieties (Chemlali Sfax and Chetoui). The obtained percentages of correct classification (superior to 97 %) proved the potential of the used method in varietal origin authentication.