The organic milk market in Germany has been growing rapidly in recent years – by as much as 34 per cent between 2006 and 2007, to reach 11 per cent of all fresh drinking milk. This popularity, coupled with shortages brought about by high demand, mean there is a risk of fraudulent labelling, according to Joachim Molkentin of the Federal Institute of Nutrition and Food in Germany.
To combat this, Molkentin and his team set out to develop a test for certain components in milk that would be drastically different in organic and conventional milk – such as the carbon stable isotope ratio, levels of alpha-linoleic acid (C18:3ω3), and conjugated linoleic acid (CLA).
The intention was not to replace controls along the process chain, but to provide monitoring services with an extra tool to apply at retail level, should it be deemed necessary.
Twice a week for 18 months, Molkentin purchased three brands of conventional milk and three brands of organic milk from German supermarkets, and analysed them for levels of carbon stable isotope ratio, ALA and CLA.
Sample analyses, which numbered 286 in total, were conducted over a long period of time so as to allow for seasonal variations in the cows’ diets – and therefore in the nutrients in the their milk.
Using isotope ratio mass spectrometry, Molkentin was able to establish threshold levels of carbon stable isotope ratio between the organic and conventional milks, of below a maximum of -26.5%. This, he wrote in the Journal of Agricultural and Food Chemistry, “would be attributable to the different percentages of maize in the respective feed”.
Maize is commonly used in organic feed in Germany. It is a so-called C4 plant – that is, uses different pathways to fixate CO2 in the atmosphere than do C3 plants. Most non-organic feeds are made up of C3 plants.
Molkentin also looked at the milk samples’ fatty acid content using gas chromatography. He was able to establish a threshold level for C18:3ω3 at above 0.50% for organic milk.
However these findings come with a strong caveat: It is applicable for Germany, but not other countries, where feed composition and environmental conditions made yield different results.
Journal of Agriculture and Food Chemistry 2009, 57 (3), pp 785–790
“Authentication of Organic Milk Using δ13C and the α-Linolenic Acid Content of Milk Fat”
Author: Joachim Molkentin