Measurement of stable isotope abundances in milk and milk ingredients — a possible tool for origin assignment and quality control

 Relative carbon and nitrogen stable isotope abundances in total milk reflect the isotopic composition of the diet fed to the dairy cows; this diet and its δ-values depend on geographical and climatic factors. Milk from regions dominated by grassland typically shows relatively negative δ13C-values, while in regions dominated by crop cultivation the δ13C-values are more positive. The δ15N-values are influenced by factors such as soil conditions, the intensity of agricultural use and the climate. Casein in authentic milk samples is enriched in both 13C and 15N as compared to total milk, while the whey fraction is slightly enriched in 13C and depleted of 15N. The isotopic content of milk, casein and whey from one location have been measured throughout a period of longer than 1 year; variations are usually not greater than 1‰. In milk water, the 18O content was increased by between 2 and 6‰ as compared to ground water.