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.