Metodi isotopici e modelli per la tracciabilità dei prodotti animali

The main elemental constituents (H, C, N, O, S) of bio-organic material have different stable isotopes (2H, 1H; 13C,12C; 15N,14N; 18O,17O,16O; 36S, 34S, 33S, 32S). Isotopic ratios can be measured precisely and accurately using dedicated analytical techniques such as Isotope Ratio Mass Spectrometry (IRMS). Analysis of these ratios shows potential for assessing the authenticity of food of animal origin. Geographical, climatic, pedological, geological, botanical and agricultural factors affect the stable isotope ratios (SIR) of bio-elements and SIR variations are ultimately incorporated into animal tissue through eating, drinking, breathing and exchange with the environment, being memorised in the resulting foods. As a consequence, the stable isotope ratios analysis of H, C, N, O and S has shown high potential for determining geographical origin, animal diet and the production system (organic/conventional) for pork, beef and poultry, milk, butter, cheese, fish and shellfish. In the case of the hard PDO cheeses Grana Padano and Parmigiano Reggiano, it is also used in real-life situations to assess the authenticity of grated and shredded cheese on the market. With this work I tried to fill in some of the research gaps found reviewing the literature on the application of the analysis of the stable isotope ratios of bioelements (2H/1H, 13C/12C, 15N/14N, 18O/16O, 34S/32S), for the traceability of animal products, in particular meat, dairy and fish. In detail, the research aimed at: • studying the variation of stable isotope ratios in blood fractions of lamb following dietary changes, • detecting the efficacy of IRMS for tracing lamb production systems in four regions of the north west of Tunisia • investigating the ability of the isotopic analysis to discriminate and trace the geographical origin of rainbow trout, • validating through a collaborative study the methods for analysing the isotopic and mineral profile of cheese, • characterising the isotopic and mineral profile of Mozzarella di Bufala PDO cheese. We found that d13Cplasma, d18Oplasma and d34Splasma of lamb were different 7 days after an abrupt switch from a pasture- to a concentrate-based diet. d15Nplasma and the isotope ratios of blood erythrocytes were not different on the different sampling dates and were not affected by the change of diet over a 14 days period. Therefore the combination of isotopic ratios of plasma and erythrocytes represents a good tool for deducing the dietary background of lambs. Indeed, erythrocytes were shown to be suitable for verifying whether the animal was actually pasture-raised and could merit a higher price, while the analysis of plasma could detect very short finishing periods in previously grazed animals. The efficacy of IRMS for tracing lamb production system was investigated in four regions of the north west of Tunisia, characterized by herbaceous pasture. The isotopic profiles of the Tunisian lamb meat types provided useful signatures for a satisfactory traceability of the lamb meat samples produced in Tunisia (sensitivity = 1.00). However, the differences between them were not sufficient and systematic to be validated by an external set of samples including 10 Italian lamb types. For investigating the ability of the isotopic analysis to trace the geographical origin of fish, we measured the isotopic ratios of H, C, N, O and S in defatted fillet and the extracted lipid fraction from farmed rainbow trout reared in different Italian farms and with two types of feeds: high fish content (HF) and low fish content (LF) feeds. The aim was to investigate the ability of isotopic analysis to discriminate and trace the geographical origin of trout from two regions of northern Italy (Friuli Venezia Giulia and Trentino), also according to the type of feed. We found that the C, N and S isotope ratios of feed and fillet were highly positively correlated among and between each other, and negatively correlated with the d2H and d18O of feedand with the d2Hfat of fillet, which were in their turn highly interrelated. The d2H and d18O of fillet were interrelated and positively correlated with d18Owater. In comparison with other variables, the d18Ofat of fillet showed less significant correlation with the other isotopic parameters. Good discrimination was found between trouts according to the type of feed and with the origin. For validating the isotopic and elemental analytical methods, an international collaborative study based on blind duplicates of 7 hard cheeses was performed according to the IUPAC protocol and ISO Standards 5725/2004 and 13528/2005. The H, C, N and S stable isotope ratios of defatted cheese determined using IRMS and the content of Li, Na, Mn, Fe, Cu, Se, Rb, Sr, Mo, Ba, Re, Bi, U in cheese after acid microwave digestion using ICP-MS were analysed in 13 different laboratories. The average standard deviations of repeatability (sr) and reproducibility (sR) were defined for both the isotopic and the mineral variables. The validation data obtained here can be submitted to the standardisation agencies to obtain official recognition for the methods, which is fundamental when they are used in commercial disputes and legal debates. This is very important for PDO cheeses, such as the Parmigiano Reggiano and Grana Padano, which cost more than double the generic similar cheeses and must be protected against mislabelling. A first evaluation of the isotopic and mineral data measured in buffalo milk and corresponding Mozzarella di Bufala Campana PDO, highlights the importance of the d18O and d2H values of casein, as well as of the content in Rb for tracing the origin of these products