Application of multi-element (C, N, H, O) stable isotope ratio analysis for the traceability of milk samples from China.

Cow milk samples from various provinces in China were collected, and the effects of lactation stage, sampling time, and geographic origin on the samples were studied by elemental analysis-isotope ratio mass spectrometry (EA-IRMS). Traceability accuracy was determined using δ13C, δ15N, δ2H and δ18O values to specifically assign geographic origin. Stable isotope ratios of C, N, H and O were not significantly different among three lactation stages; however the δ13C, δ15N, and δ18O values of milk were influenced by sampling time. Furthermore, there were highly significant regional differences in the mean δ13C and δ15N values of milk. In summary, the lactation stage had no effect on the traceability of milk, whereas sampling time and geographic origin did affect milk traceability. Different geographic locations with a separation distance greater than 0.7 km can be distinguished using multi-element (C, N, H, O) stable isotope ratio analysis.