Stable isotope ratio analysis for the traceability of raw and cured meat

The effect of different factors on the stable isotope ratio (SIR) variability of the most important bioelements (2H/1H, 13C/12C, 15N/14N, 18O/16O, 34S/32S), measured using IRMS (Isotopic Ratio Mass Spectrometry), was evaluated in different types of tissues, including pig and ovine muscles, muscle lipids and lipid fractions. To evaluate the effect of tissue turnover on the different isotope ratios, in a diet-switch experiment, 28 lambs were switched to an isotopically distinct diet and raised on two different energy allowances (high energy allowance (HEA) with a target weight gain of 150 g/day or low energy allowance (LEA) with a target weight gain of 50 g/day). Determination of multiple stable isotope ratios (δ2H, δ13C, δ18O and δ34S) in ovine muscle indicated diet-muscle fractionations prior to the diet-switch to be -44.0‰ +1.9‰ and 0‰ for H. C and S respectively. The muscle sampled from animals on the HEA recorded higher δ13C values than muscle from animals on the LEA (p = 0.0003). The δ18O values in ovine muscle were largely influenced by the water ingested while most of the H used to build ovine muscle tissue depend on the feed rather than the drinking water. The discrimination between intra muscular lipid and diet was estimated to be -172.7, -1.3‰ and -11.5‰ for H, C and O respectively. The C half-lives of muscle were determined to be 75.7 and 91.6 days for animals receiving the high and low EA respectively and it is comparable with S half-lives measured in ovine LD. However, the estimated half-lives of lipids were too long to be used for tracking short term dietary changes in lambs and probably also in other meat animals. In a second experiment the stable isotope ratios of bioelements in defatted dry matter and marbling and subcutaneous fat fractions were assessed in 86 ham samples belonging to six different types, with the aim of ascertaining the effect of origin and the production system on 11 isotopic ratios. The ham types were obtained from pigs reared in three regions, examining one different production factor in every location, at two levels of expression: pig genotype (local breed vs. industrial hybrid) in Friuli (Italy), pig feeding regime (Bellota vs. Campo) in Extremadura (Spain) and ham seasoning time (mid vs. end) in Emilia (Italy). The isotopic composition of meteoric water and the dietary abundance of C4 plants made it possible to distinguish Italian PDO from Spanish hams. Higher δ15N values in local breeds than in industrial hybrids might indicate relatively more nitrogen excretion, due to a higher ratio between protein degradation and protein synthesis. The Strecker degradation of sulfur amino acids taking place during seasoning and generating dimethyl disulfide and other similar volatile compounds can explane δ34S isotopic fractionation showed to compare the End-seasoned Italian hams vs mid-seasoned ones. The contrasting treatments within the regional batches generated promising differences in SIR, potentially useful for tracing the whole ham production system, including the processing procedure. In a third experiment the stable isotope ratios of five bio-elements - H, O, C, N and S - were analysed in the protein and fat muscle fractions of sixty beef carcasses from zebu cattle reared in an tropical African country (Cameroon) with the scope of evaluating the effect of this specific origin on the different isotopic ratios. Zebu beef from Cameroon was shown to have a specific isotope profile, characterised by lower δ13C, δ2H and δ18O values than those reported for other areas around the world, as a consequence of the almost exclusive use of tropical C4 pasture grass for cattle feed and the geographic and climatic gradient in the isotope composition of precipitation. The isotopic composition of the fat fraction of muscle, and in particular the δ2H and δ13C values of fat, was significantly affected by the subcutaneous fat colour. The zebu with a white subcutaneous fat (“white type”) showed a clear tendency to be more enriched in 2H isotopes and more depleted in 13C isotopes than the “yellow type” , while the “cream type” presented an intermediate condition. These trends are correlated with fat composition. Within the Cameroon, multi-element analysis gave promising results for tracing the regional origin of beef and some aspects of the cattle breeding system, such as the nutritional status of animals. On the basis of the results of this study all of the considering factors can have effect on the different isotope ratios but with different weight. Origin and type of diet outweigh turnover and technical process of products, even if they must be carefully considered to prevent possible mistake during the results evaluation.