Combining different biomarkers to distinguish Chemlali virgin olive oils from different geographical areas of Tunisia.

BACKGROUND: Despite their high potential, Tunisian virgin olive oils (VOOs) are mainly exported in bulk or blended with VOOs of other origin, hindering their international market placement. To face this situation, their valorization is needed by highlighting their unique features and by developing tools to guarantee their geographical authenticity. Compositional features of Chemlali VOOs produced in three Tunisian regions were assessed to identify suitable authenticity markers. RESULTS: Quality indices ensured the quality of the VOOs studied. Volatile compounds, total phenols, fatty acid (FA) and chlorophylls are significantly influenced by the region of origin, which was justified by the differences found in soil and climatic conditions of the three geographical regions. To explore the capabilities of these markers for the geographical authentication of Tunisian Chemlali VOOs, classification models based on partial least squares-discriminant analysis (PLS-DA) were developed by grouping the minimum number of variables allowing the highest discrimination power, minimizing in this way the analytical procedure. The PLS-DA authentication model based on combining volatile compounds with FA or with total phenols achieved a correct classification of 95.7% of the VOOs according to their origin, as assessed by 10%-out cross-validation. Sidi Bouzid Chemlali VOOs achieved 100% of correct classification, while the misclassification between Sfax and Enfidha ones did not exceed 10%. CONCLUSIONS: These results allowed to establish the most promising and affordable combination of markers for the geographical authentication of Tunisian Chemlali VOOs from distinct production regions and provide the basis to further develop authentication models based on wider datasets. © 2023 Society of Chemical Industry.

Evolution of sesquiterpene hydrocarbons in virgin olive oil during fruit ripening.

Despite the potential of sesquiterpene hydrocarbons in olive oil authentication, their metabolism in Olea europaea is poorly understood, and little is known about their biochemical regulation in olives as a function of ripening. To ascertain some metabolic relationships between sesquiterpene hydrocarbons and olive ripening, the content of sesquiterpene hydrocarbons was assessed in virgin olive oils from two olive varieties grown in the same geographical area and produced at different harvesting periods. During the ripening, the accumulation of sesquiterpenes in the olive itself, and thus in the oil, differed according to their molecular structure: bicyclic sesquiterpenes, showed decreasing concentrations the later the harvest, while acyclic farnesene-like compounds progressively increased through the olive ripening process. This is first evidence that the accumulation of sesquiterpene hydrocarbons in olive, and hence in olive oil, is modulated during ripening. Therefore, the degree of ripening of olives should be taken into consideration when considering the sesquiterpenic profile of virgin olive oil for their authentication.

Influence of olive maturity stage and geographical origin on some minor components in virgin olive oil of the chemlali variety.

Minor compounds such as sterols, aliphatic alcohols, tocopherols, and chlorophylls in virgin olive oil from Chemlali cultivar were analyzed during the maturity process. The study concerns oils from the following three different olive growing areas of Tunisia: Sfax, Sidi Bouzid, and Enfidha. Analytical results showed that both the maturity process and the olive provenances influence the evolution of the content of these compounds.

Volatile compounds characterizing Tunisian Chemlali and Chétoui virgin olive oils.

A total of 33 virgin olive oil samples of the two main Tunisian cultivars, Chemlali and Chétoui, were characterized by their volatile compounds. The olive oil samples were obtained from olives harvested at four stages of ripeness in costal and inland farms of different geographical places. Major volatiles, mostly C6 and C5 compounds produced from linolenic and linoleic acids through the lipoxygenase cascade, were quantified by solid-phase microextraction-gas chromatography. Mathematical procedures allowed for the determination of the volatiles that not only are able to discriminate the olive oils by their olive cultivar (hexanal, E-2-hexenal, and total ketones) and ripeness (pentanal and 1-penten-3-one) but also contribute to their distinctive aroma. Finally, an electronic nose based on metal oxide sensors was checked for a rapid and at-line implementation of Tunisian olive oil varietal traceability. The classification of the samples by the sensors was explained by their sensitivity to volatiles E-2-hexanal, hexanal, 1-penten-3-one, ethanol, and Z-3-hexenol. Multivariate procedures of discriminant analysis and principal component analysis were used in the study.