Delta 13C- and delta 18O-Values of glycerol of food fats.

The average values of carbon and oxygen isotopic contents (delta C-13 and delta O-18) of 36 glycerol samples from fats have been determined. The examined samples arise from many fats of animal and plant origin, as well as from the three Italian hard cheeses Parmigiano-Reggiano, Grana Padano and Trentingrana. 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, observed for Parmigiano-Reggiano, Trentingrana and Grana Padano. Additionally, the mean total O-18 content of glycerol samples of vegetable origin is approximately 23.8 parts per thousand, while that from animal fat is 15.1 parts 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 relative to the fat glycerol of the three cheeses might be considered a potential criterion of authentication.