Towards the geographical traceability of the Italian walnut: a case study based on stable isotopes signatures (δ2 H, δ18O, δ13C, δ15N, δ34S) and elemental fingerprinting

Juglans regia (L.) is cultivated worldwide for its nutrient-rich nuts. Italy is among the top five importing countries of walnuts in shell due to the strong decline in the Italian walnuts production in the early seventies, combined to a constantly growing demand. The current context is therefore favourable to promote the development of a local high-quality Italian walnut production. In this respect, tools capable of tracing the origin of walnut can support the process of valorisation and promotion of this product. The main aim of this study was to investigate to what extent stable isotope data (H, O, C determined in the lipid and defatted fractions, N and S of the defatted fraction) coupled with 56-element profiles could be used to differentiate Italian walnuts on a regional and global level. A total of 122 walnut samples from six countries and two years of harvest were analysed. Multivariate data analysis (JIVE) suggested a strong effect of the geographical origin, particularly at the regional level. However, it was not possible to completely exclude the effect of the harvest year on the overall variability of the samples. A preliminary analysis focussing on a regional scale (Italian samples only) and on a few samples of international origin, confirmed that the proposed approach could be potentially applied for the discrimination of Italian walnuts. Overall, the results presented support the effectiveness of stable isotopes and multi-element analyses in walnut traceability and local origin protection.