CHARACTERIZATION OF GLYCEROL FROM DIFFERENT ORIGINS BY H-2-NMR AND C-13-NMR STUDIES OF SITE-SPECIFIC NATURAL ISOTOPE FRACTIONATION

The site-specific natural isotope fractionation of carbon and hydrogen has been investigated by SNIF-NMR for glycerol samples, extracted fro m plant lipids, obtained in the fermentation of sugars, or from commer cial sources. In the first two cases, several plant species from eithe r C-3 or C-4 metabolic origin have been considered. Large deviations w ith respect to a statistical distribution of deuterium in the glycerol skeleton are observed and the dispersion ranges of the isotopic param eters are much larger than the precision of the measure. The NMR deter mination of the site-specific carbon isotopic parameters (positions 2 and 1,3 of glycerol) provides an easy method for distinguishing natura l and synthetic samples. More generally, the discriminating potential of the carbon and hydrogen isotopic fingerprint of glycerol has been e stimated on a statistical basis in terms of the nature of the raw mate rial (plant oil or sugar fermentation) and, in each case, in terms of C-3 or C-4 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.