Stable isotope ratio analysis of lactose as a possible potential geographical tracer of milk

With the aim of evaluating the power of the stable isotope ratio analysis of milk lactose as a possible geographic tracer, one hundred and twenty (120) samples of authentic milk from different European countries (Italy, Germany, Austria, France, Spain) were analyzed. The lactose of each was separated and fermented to obtain the alcohol which was analyzed to determine the stable isotope ratios (D/H)I, (D/H)II and δ13C. The δ13C values showed a close correlation with the diet followed by the animal (C3 and/or C4 plants) while the (D/H)I ratio was more correlated with the δ18O of drinking water and therefore with the geographical origin of the milk. Significant differences were found in the (D/H)II ratio of alcohol obtained from the same lactose through the use of different yeasts. The analysis of the δ18O of the bulk milk and of the water drunk by the animals showed how the two parameters are closely correlated with each other with differences that can vary according to the type of farm (grazing or not). The method reported here has been validated by two different European laboratories in terms of repeatability and reproducibility.