Stable Isotope and Fatty Acid Analysis of Organic vs. Conventional Milk

Background and methodology:

With increasing sales of organic milk, intensified tests for authenticity are required. Analytical methods to identify organic milk, therefore differentiating it from conventional milk, are needed for consumer protection. Because the composition of milk fundamentally depends on how cows are fed, 35 samples from both production systems in Germany, including farm and retail milk, were collected within a 12-month period, to reflect seasonal variation. Appropriate properties were analyzed.


Fatty acid analysis distinguished organic milk completely from conventional milk because of the higher α-linolenic acid and eicosapentaenoic acid content in organic milk. Analysis of stable carbon isotopes also separated organic from conventional milk because of the different amounts of corn in the diet of the cows. The researchers suggested that such tests would be easier at the retail level because compositional variation of dairy milk is smaller at the farm level.


Molkentin, J. & Giesemann, A. (2007). Differentiation of organically and conventionally produced milk by stable isotope and fatty acid analysis. Analytical and Bioanalytical Chemistry, 388(1), 297-305. Available on-line at: