Stable isotope ratios of H, C, N and O in Italian citrus juices

Stable isotope ratios (SIRs) of C, N, H and O have been exensively used in fruit juices quality control (ENV and AOAC methods) to detect added sugar and the watering down of concentrated juice, practices prohibited by European legislation (EU Directive 2012/12). The European Fruit Juice Association (AIJN) set some reference guidelines in order to allow the judging of the genuiness of a juice. Moreover, various studies have been carried out to determine the natural variability of SIRs in fruit juices, but none of these has investigated SIRs extensively in authentic citrus juices from Italy. In this study authentic citrus juice samples were officially collected in Italy by the Italian Ministry of Agricultural and Forestry Policies from 1998 onwards for a total of about 500 samples. The samples were investigated for their content of (D/H)I and (D/H)II in ethanol and δ13Cethanol, δ13Cpulp, δ13Csugars, δ18Ovegetalwater, δ15Npulp, and δ18Opulp using Site-Specific Natural Isotope Fractionation-Nuclear Magnetic Resonance (SNIF NMR) and Isotope Ratio Mass Spectrometry (IRMS), respectively. Here are presented the characteristic ranges of variability in SIRs in genuine Italian citrus juice samples as well as their relationships, and compliance with the limits indicated by the AIJN and others proposed in the literature. In particular, the Italian range of values was found to be not completely in agreement with AIJN guidelines, with the risk that genuine juices could be judged as not genuine. Variety seems not to influence SIRs, whereas harvest year and region of origin have some influence on the different ratios, although their data distribution shows overlapping when principal component analysis is applied.