Authentication and traceability of Italian extra-virgin olive oils by means of stable isotopes techniques

The aim of this work was to explore the variability of carbon and oxygen isotopic compositions (?13C and ?18O, respectively) of extra-virgin olive oils, originated from different areas of Italy, in relation to different and contrasting environmental conditions. About 400 samples of extra-virgin olive oils from nine different Italian regions, ranging from North to South, and from three different years of production (2009, 2010, 2011) were analysed. Statistical analysis of data shows correlations among oil isotopic compositions with latitude, mean annual temperature and mean annual precipitation of the different areas of origin. No correlations were found by comparing variability of isotope compositions versus that of both elevation and longitude. An observed shift of the oil ?18O per centigrade degree of the mean annual temperature is congruent with those previously reported in literature. The effect of year of oil production was found to be significant, both for ?18O and ?13C. Olive oil samples from the insular regions, Sicily and Sardinia, resulted more enriched in 13C and 18O than those produced in the northern region, Lombardia. The squared Euclidean distance calculation applied on the analytical data exhibited a good clustering of the extra-virgin olive oils grouped on the basis of their geographical origin.