Stable Isotope Ratios of H, C, N and O in Italian citrus juices

Authenticity has always been a major concern of national regulatory bodies and consumers. The stable isotope ratios (SIR) of C, N, H and O have been intensively used in food quality control and specifically for fruit juices (ENV and AOAC methods), allowing detection of added sugar and the watering down of concentrated juice, practices prohibited by European legislation (EU Directive 2012/12). In this context various studies have been carried out to determine the natural variability of SIRs in fruit juices, but none of these has investigated SIRs in authentic citrus juices from Italy. In this work we considered about five hundred citrus juice samples officially collected in southern Italy by the Italian Ministry of Agricultural and Forestry Policies since 1996. Pulp and sugar fractions were separated from the samples and ethanol resulting from sugar fermentation was obtained by distillation. (D/H)I and (D/H)II in ethanol and d13Cethanol, d13Cpulp, d13Csugars, d18Ovegetalwater, d15Npulp, d2Hpulp and 18Opulp were determined using Site-Specific Natural Isotope Fractionation-Nuclear Magnetic Resonance (SNIF-NMR) and Isotope Ratio Mass Spectrometry (IRMS) respectively. Here we present the characteristic ranges of variability for SIRs in genuine Italian citrus juice samples. We evaluated the relationships among SIRs as well as their compliance with the limits indicated by the official methods and furthermore the possibility of distinguishing the region of origin