The site-specific natural isotope fractionation of carbon and hydrogen has been investigated by SNIF-NMR for glycerol samples, extracted from plant lipids, obtained in the fermentation of sugars, or from commercial sources. In the first two cases, several plant species from either C3 or C4 metabolic origin have been considered. Large deviations with respect to a statistical distribution of deuterium in the glycerol skeleton are observed and the dispersion ranges of the isotopic parameters are much larger than the precision of the measure. The NMR determination of the site-specific carbon isotopic parameters (positions 2 and 1,3 of glycerol) provides an easy method for distinguishing natural and synthetic samples. More generally, the discriminating potential of the carbon and hydrogen isotopic fingerprint of glycerol has been estimated on a statistical basis in terms of the nature of the raw material (plant oil or sugar fermentation) and, in each case, in terms of C3 or C4 metabolism of the precursor. Glycerol may be proposed as an isotopic probe for discriminating between olive and sunflower and for investigating the adulteration of wines. Keywords: Fermentation; edible oils; origin assessment; authenticity

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Deuterium NMR study of the origin of hydrogen in fatty acids produced in vivo by chickenThe origin of hydrogen in fatty acids produced in vivo by chicken was studied by using isotope tracing monitored by 2 H NMR. Chickens were fed with deuterium-labeled water, deuterium-labeled glucose/fructose and trideuterated acetate. The site-specific isotope distribution of the fatty acids produced in vivo by the chickens was analyzed after transformation into methyl esters. A connection was observed between the hydrogen atoms of the feeds and water and those of the different molecular positions of the fatty acids produced by chicken. Water hydrogen makes an important contribution to the formation of the lipids. The hydrogen of the enzyme-bound acetyl or malonyl moiety in acyl-CoA may be transferred from the C-1, C-2 or C-6 of glucose or fructose and indirectly from water. The hydrogen introduced by the cofactor NADPH may be abstracted from C-1 and C-3 of glucose, through its regeneration in the pentose phosphate metabolism pathway, and contains hydrogen atoms of water. The exogenous acetate enters into the in vivo fatty acid biosynthesis pathway in an efficient way and can make an important contribution to the biosynthesis of the lipids.