The stable isotope ratios (delta13C, delta15N, and delta34S of casein and delta13C and delta18O of glycerol) measured by IRMS of French, Italian, and Spanish cheeses are presented and discussed. Variability factors such as animal-feeding regimen, geographical origin, and climatic and seasonal conditions were studied to check the possibilities of cheese characterization offered by each isotopic parameter. Delta13C values of both casein and glycerol appeared to be strongly correlated to the amount of maize in the animal diet. Delta15N and delta34S of casein proved to be mostly influenced by the geoclimatic conditions of the area (aridity, closeness to the sea, altitude). Delta18O of glycerol was more dependent on the geographical origin of the cheeses and on climatic/seasonal parameters. By applying a multivariate stepwise canonical discriminant analysis, good discrimination possibilities for the different European cheeses were obtained, confirmed by the classification analysis, when >90% of the samples were correctly reclassified.

The isotopic investigation of vanillin has been extended to the new sources of natural precursors of vanillin recently introduced with a view of obtaining natural vanillin by biotechnological processes. To check the consistency of the isotopic composition of vanillin with that of the corresponding aromatic fragment, a selective degradation reaction into guaiacol was carried out. The reaction was shown to proceed without significant isotopic fractionation at the sites of interest, and an optimized procedure was defined from the results of an experimental design involving the quantity of reagent and the temperature and duration of the experiment. Guaiacol, which can be easily obtained in a reasonable time, is an interesting isotopic probe for carbon- and oxygen-isotope ratio mass spectrometry (IRMS) determinations. It provides (13)C information specific to the aromatic fragment and, combined with delta(13)C values measured on vanillin itself, it improves the authentication potential of carbon-IRMS. Thus, the natural status of ferulic acid may be characterized by significant (13)C depletion at the formyl site. Similarly, the oxygen-18 content of guaiacol is a better authentication tool than delta(18)O of vanillin because it does not suffer the drawback of being altered by chemical exchange of the sp(2) oxygen atom with water in industrial or laboratory procedures. Although collaborative studies are still necessary to improve the interlaboratory reproducibility of the delta(18)O parameters, consistent results can be obtained in an intralaboratory context. It is shown in particular that chemical oxidation of ferulic acid is characterized by a relative enrichment of the aromatic moiety of vanillin.

Variability within the stable isotope ratios in various lipidic fractions and the fatty acid composition of muscle oil has been analyzed for a large sample (171 fish) of wild and farmed Atlantic salmon ( Salmo salar) from 32 origins within Europe, North America, and Tasmania. Sampling was extended over all seasons in 2 consecutive years and included fish raised by different practices, in order to maximize the range of variation present. It is shown that two readily measured parameters, delta 15N measured on choline and delta18 O measured on total oil, can be successfully used to discriminate between fish of authentic wild and farmed origin. However, the certainty of identification of mislabeling in market-derived fish is strengthened by including the percentage of linoleic acid C18:2n-6 in the lipidic fraction. Thus, several apparent misidentifications were found. The combination of these three analytical parameters and the size of the database generated makes the method practical for implementation in official laboratories as a tool of labeling verification.

Autoxidation of sulfite is catalyzed by the water-soluble complex (meso-tetrakis(4-N-methylpyridiniumyl)porphyrinato)manganese(III) (Mn-TMPyP), leading to an intermediate species capable of hydroxylation of p-isopropylbenzoic acid, epoxidation of carbamazepine, and generation of single-strand breaks both in plasmid ΦX174 DNA and in a 167-base-pair fragment of pBR322. 18O-Labeling studies confirm that the high-valent manganese−oxo intermediate undergoes oxo−hydroxo tautomerism in competition with oxidation of substrate or reduction by excess sulfite. In contrast to the classical reductive activation of dioxygen by metalloporphyrins (dithiothreitol or ascorbate in the presence of O2), a mechanism is proposed in which SO3 •-, formed by oxidation with MnIII, is trapped by O2, leading to a species (SO5 •-) capable of generating a MnVO complex. Importantly, these studies point to the use of an alternative, biocompatible oxidation system compared to the preformed oxidant KHSO5.