Development and implementation of stable isotope ratio analysis in bulk products and sub-components to ensure food traceability

Objective assessment of food authenticity has become of paramount importance today, with an increasing demand for analytical methods able to provide proof of origin and prevent food adulteration. In order to achieve this goal, the European Union has reinforced control activities and investigated new methods able to support food characterisation and geographical traceability. Stable isotope ratio analysis of so-called bioelements such as hydrogen, carbon, oxygen, nitrogen and sulfur has been used since the 1990s for food authenticity control of different premium products. Application of isotopic composition is based on evidence that the isotopic signature is affected by various environmental factors, such as photosynthetic and nitrogen cycles, the pedological characteristics of soils, agricultural practices, botanical origin, geographical origin and climatic or hydrological conditions. In this study, isotope ratio mass spectrometry methods were developed to characterise and determine the authenticity of cereal crops, pasta, wine, balsamic vinegar, oenological tannins and extra-virgin olive oils. In particular, isotopic variability measured along the Italian pasta production chain allowed good discrimination in relation to geographical provenance. δ2H, δ18O and δ13C were shown to be significantly correlated to geographical factors (e.g. longitude), whereas δ15N and δ34S were affected by geology and fertilisation practices. Measurement of amino acid δ15N and δ13C values improved discrimination of conventional and organic wheat compared to stable isotope ratio analysis of bulk. Variability in the δ15N value was checked along the entire oenological chain for the first time. The study included evaluation of the effect of the fermentation process using different types of yeast, the addition of nitrogen adjuvants and ultrasound lysis simulating wine ageing. Despite nitrogen isotope fractionation observed from soil to wine through the plant, the δ15N value of proline conserved the nitrogen isotopic fingerprint of the growing soil and can therefore be used as an additional isotopic marker to trace the geographical origin of wine. The same analytical approach, when applied to commercial tannin samples, made it possible to characterise them based on botanical origin. The δ13C values were shown to be significantly more negative in tannins from grapes, tea and acacia and less negative in tannins from oak. Furthermore, the 2H/1H and 13C/12C stable isotope ratios of acetic acid and the 18O/16O of water were investigated in “aceto balsamico di Modena IGP” (ABM) samples. No isotopic variation was observed along the ABM production chain, providing experimental evidence that such analytical parameters, used routinely for wine, can also be used for ABM in authenticity studies. Finally, the 2H/1H, 13C/12C and 18O/16O of extra-virgin olive oils were analysed in bulk samples and compounds, specifically in fatty acids. The results showed that in some cases bulk analysis was able to discriminate between different countries on the basis of specific geo-climatic conditions. Moreover, both the 13C/12C and 2H/1H values of the main fatty acids allowed good discrimination between European and non-European extra-virgin olive oils. To conclude, the methods developed for the specific commodities considered can be proposed as suitable tools for the detection of mislabelling and for consumer protection, demonstrating that isotopic analysis can effectively contribute towards distinguishing the authenticity of commercial food samples.