Is phytanic acid a suitable marker for authentification of milk and dairy products from grass-fed cows or organic farming systems?

Cow milk samples were collected from herds of 30 Dutch farms and analysed by gas chromatography-mass spectrometry for phytanic acid (PHY) and its diastereomers SRR and RRR to test the hypothesis that PHY could be a suitable marker for authentification of milk from grass-fed cows. The samples differed in the proportion of fresh grass in the cows’ daily dry matter intake (0 to 94%). Grass was either fed indoors or grazed (during daytime, or day and night). Of the latter category, three farms had an organic and three a biodynamic farming system. PHY concentrations were not significantly higher in organic/biodynamic milk compared with conventional milk, nor were they correlated with the proportion or amount of fresh grass in the diet. The proportion of RRR in total PHY was positively correlated with the proportion of fresh grass in the diet. These results indicate that, in contrast to our hypothesis, PHY content is not a suitable indicators of pasture grazing or organic/biodynamic farming, while the proportion of diastereomers of PHY may be useful as such.