l(+)-tartaric acid of grape origin: Definition of threshold limits for the 13C/12C and 18O/16O stable isotope ratios and validation of the isotopic method through an interlaboratory study

L(+)-tartaric acid is one of the most used additives in the oenological practices. Its properties make it useful as preservative and acidulant in grape-derived products. This additive can be obtained through the extraction from grapes, from other fruits or through synthesis from petrochemical sources. In Europe, only L(+)-tartaric acid from grapes can be added to wine products, but the price difference between the forms could lead to the fraudulent use of the cheaper synthetic L(+)-tartaric acid. In other continents where such limitation is not applied, the clear commercial identification of the products is still desirable. Stable isotope analysis of carbon (δ13C) and oxygen (δ18O) proved to be a robust and effective method in discriminating between synthetic and grape-derived L (+)-tartaric acid. In this study, to define the threshold limits of δ13C (above − 24.8 ‰) and δ18O (above +25.6 ‰) of grape-derived L(+)-tartaric acid, a database consisting of 81 authentic natural samples was created. Moreover, the validation of the isotopic method through an interlaboratory study involving nine European and extraEuropean laboratories, was provided. The repeatability and the reproducibility standard deviation of the method were calculated.