delta C-13- and gamma O-18-values of glycerol of food fats

The average values of carbon and oxygen isotopic contents (delta C-13 and d elta O-18) of 36 glycerol samples from fats have been determined. The exami ned samples arise from many fats of animal and plant origin, as well as fro m the three Italian hard cheeses Parmigiano-Reggiano, Grana Padano and Tren tingrana. The total C-13 content allows one to distinguish between glycerol from plants with the C-4 carbon fixation pathway (maize, mean delta C-13 = -14.4 parts per thousand) and that from plants with the C-3 pathway (mean delta C-13 = -30.7 parts per thousand). The delta C-13-values of glycerols of animal origin seem to depend on the diet of the animal, as suggested by the mean values -29.6, -29.0 and -25.1 parts per thousand, respectively, ob served for Parmigiano-Reggiano, Trentingrana and Grana Padano. Additionally , the mean total O-18 content of glycerol samples of vegetable origin is ap proximately 23.8 parts per thousand, while that from animal fat is 15.1 par ts per thousand. However, the delta O-18 mean values relative to Parmigiano -Reggiano, Grana Padano and Trentingrana are 11.8, 16.0 and 13.8 parts per thousand, respectively. The combination of the C-13 and O-18 measurements r elative to the fat glycerol of the three cheeses might be considered a pote ntial criterion of authentication. Copyright (C) 2001 John Wiley & Sons, Lt d.