87Sr/86Sr isotopes in grapes of different cultivars used as a geochemical tool for geographic traceability of agriculture products

The increasing demand of high quality food products promoted the development of rigid regulations for certification of authenticity and protection from frauds. This is leading to an increasing request of suitable scientific protocols able to confirm the authenticity of food products by tracking their geographical origin. Respect to stable isotopic composition of light elements (H, C, O, N, B), the isotopes of heavy elements (Sr, Pb) have the advantage to correlate directly with the geological and pedological substrata of farms with no effects related with climatic variations. In the last decades, among the different food products, radiogenic heavy isotopes for tracing geographic provenance of wine was heavily investigated. These studies focused on finding relationships between the final product and their area of provenance, but none of them investigated in detail the possible differences in 87Sr absorption from the bioavailable fraction of the soil by the different cultivars and vine genotypes. Here we present a detailed study on an extensive grape inter-varietal and site-specific study to implement the knowledge about vine geographical identification with Sr isotopes. 87Sr/86Sr of fresh red and white grapes, soils and rocks from three selected vineyards with similar but isotopically distinct geological substrata were determined. The research was performed on fruits from four consecutive harvest years on grapes of various genotypes from vineyards developing on three different geologic substrata. Results show that 87Sr/86Sr does not change through the years and reflects the one of the soil of production bioavailable fraction. Moreover its absorption from the soil is not influenced by the vine genotype/isotopic fractionation induced by the different vine genotype. These findings further demonstrate the reliability of this tool, even at a very small scale, for food products geographic origin assessment, being the strontium isotopic signature in grape exclusively acquired from the soil, and then strictly related to the local geology.