Climatic factors influencing the isotope composition of Italian olive oils and geographic characterisation.

The purpose of this study was to investigate the possibility of identifying oil source areas by means of simple measurements on the natural samples avoiding time-consuming sample treatments. The oxygen and carbon isotopic values of 150 samples of extra-virgin olive oil from eight different Italian regions and from three different years of production were measured according to well-established techniques. Statistical treatments of the results obtained show a very good correlation of the delta(18)O of oil with latitude, mean annual temperature, and mean relative humidity at the collection site. No correlation is found with elevation and mean annual precipitation. The shift of the oil delta(18)O per degree centigrade of the mean annual temperature is quantitatively close to that calculated for atmospheric precipitation in continental areas. Accordingly, in our measurements, the year of oil production can be identified on the basis of the delta(18)O value (mean 2004 temperatures were higher than 2005 temperatures). On the contrary, the oil delta(13)C values show no correlation with the above variables but only with latitude and, consequently, are less suitable for discriminating the geographic origin of oil. However, the delta(13)C values are suitable to indicate biological differentiation while the delta(18)O values are not. Copyright 2009 John Wiley & Sons, Ltd.