To gain information about the geographical origin of oil samples, measurements of delta(13)C and delta(18)O of the whole oil and some of its fractions have been performed on samples coming from fruits of Olea europaea L. produced in Greece, Morocco, Spain, Italy, Tunisia, and Turkey. The results obtained by applying statistical procedures have given pieces of evidence that oil samples have shown the trend to cluster according to the different climatic areas of growing environment of fruits. Some confusion has been observed for samples coming from neighboring countries having similar climates.
A review of the global cycle of methane is presented with emphasis on its isotopic composition. The history of methane mixing ratios, reconstructed from measurements of air trapped in ice-cores is described. The methane record now extends back to 420 kyr ago in the case of the Vostok ice cores from Antarctica. The trends in mixing ratios and in delta13C values are reported for the two Hemispheres. The increase of the atmospheric methane concentration over the past 200 years, and by 1% per year since 1978, reaching 1.7 ppmv in 1990 is underlined. The various methane sources are presented. Indeed the authors describe the methane emissions by bacterial activity under anaerobic conditions in wet environments (wetlands, bogs, tundra, rice paddies), in ruminant stomachs and termite guts, and that originating from fossil carbon sources, such as biomass burning, coal mining, industrial losses, automobile exhaust, sea floor vent, and volcanic emissions. Furthermore, the main sinks of methane in the troposphere, soils or waters via oxidation are also reported, and the corresponding kinetic isotope effects.
Stable isotopes are now increasingly used for the control of the origin or authenticity of food products. Among these techniques, the measurement of the
Natural stable isotope ratios for carbon, hydrogen and oxygen depend on the origin of the studied chemical compound. Such a precept is the basis of the control of the authenticity of food and especially alcoholic beverages. 13C/12C analysis of ethanol as well as 180/160 determination of water contained in wines from different European countries underline the importance of the photosynthetic pathway as well as of the environmental and climatological conditions of the vine. Interesting results in agreement with isotopic fractionation rules for the geographical origin of the samples were obtained. That encouraged us to propose the establishment of a database for isotopic parameters in wines. Stable aboutisotope ratio analysis can yield information the origin of a chemical compound. Natural stable isotope"abundances for elements such as H , C and 0 show small but measurable variations ( Fig. 1) due to isotopic fractionation which occurs during the chemical and physical processes of the natural cycles. '-4 The primary carbon pools in nature are HCO; in the hydrosphere and C 0 2 in the atmosphere. The use of isotope ratio mass spectrometry (IRMS) applied to the carbon bioelement has underlined the I3C discrimination of plants.In C3 plants, including the vine (Calvin photosynthetic cycle), the interstomatal diffusion of C 0 2 and also its dissolution cause negligible isotopic fractionation compared to the carboxylation of ribulose 1,5-biphosphate. Therefore C3 plants show a 6I3C range between -32%, and -25%0 PDB (Pee-Dee Belemnite, SC, USA).5*6 In the C4 plants (Hatch and Slack photosynthetic cycle) both the interstomatal diffusion of C 0 2 and the carboxylation of phosphoenolpyruvate limit the C 0 2 fixation and control the carbon isotopic content of those plant^.^,^ The so-called 'Crassulacean Acid Metabolism' (CAM) plants demonstrate an adaptation capacity in keeping with their environmental Such a difference in the stable carbon isotope content has often been used to detect adulteration of aromas and flavors, especially with gas chromat~graphy/'~C-I~C IRMS instruments,' (e.g. , sweetening of maple syrup) and also to establish the authenticity of wine products and spirit^.^. 3. I", Atmospheric O2 and C02, as well as H 2 0 , are the major sources of the oxygen element. Isotopic fractionation occurs during the various evapo-condensation processes. Clouds are lower in "0 than ocean water; meteoric waters are enriched in compared to clouds. The fermentation process causes no enrichment in the "0 content of the water. Due to the I*O enrichment of plant water compared to exogenous water (tap water), "0 measurements have also been used to ' detect the watering of wines as well as the redilution of fruit Water is the major pool of the hydrogen bioelement, too. As is observed for oxygen, an isotopic fractionation of hydrogen takes place during the evapocondensation process in the atmosphere, and during evaporation and biochemical reactions in plants. During the fermentation process an enrichment in 2H of wine water is obser...
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