Soil geochemistry, edaphic and climatic characteristics as components of Tunisian olive terroirs: Relationship with the multielemental composition of olive oils for their geographical traceability

Olive oil traceability based on the intrinsic chemical composition of the oil is becoming increasingly important due to the prevalence of fraudulent geographical labelling of olive oils. For a traceability tool to be valid, it should be based on olive oil properties that are clearly related to provenance factors. However, multielement analysis of the oil has been used as a traceability tool without any proof of a direct link between the multielemental composition and the geographical origin of the oil. In order to verify this link, Tunisian olive terroir components from the 11 major olive-producing regions were sampled to evaluate the influences of these components (especially soil and climate) on the geochemical composition of Tunisian olive oil. Overall, geochemical processes relating to strontium and rare-earth element (REE) enrichment were found to control the multelemental compositions of Tunisian soils. Even though olive oils from the 11 Tunisian olive-growing regions considered did not strongly reflect the geochemical signatures of the corresponding Tunisian soils, the concentrations of four elements in the oils, namely Fe, Ti, Ni and Ba, showed significant positive Spearman correlations with their concentrations in the bioavailable extracts from those soils. Moreover, there were numerous significant correlations of elements in the olive oil with soil chemical and climate parameters. Our results clearly confirm that the complex interactions of the olives with the climate and soil chemistry during cultivation significantly affect the multielemental composition of the resulting olive oil. This finding implies that the elemental profile of the olive oil is an effective and valid marker of the geographical origin of the oil, as it is significantly linked to oil provenance factors. It also explains the discrepancies between the geochemical signature of an oil and that of the soil in which the olives were grown, as climate parameters affect the transfer of that signature from soil to olives. This work therefore provides the basis for a scientifically based approach to olive oil traceability. The results of this work can be utilized by agricultural authorities to realise the multielement-based traceability of olive oils from various Tunisian regions. Graphic abstract