Phytanic and pristanic acid content in Dutch farm milk and implications for the verification of the farming management system

Bovine milk samples were collected from 30 Dutch farms and analysed by gas chromatography-mass spectrometry for phytanic acid (PHY), pristanic acid (PA) and SRR/RRR-diastereomers ratio of PHY. The samples differed in the percentage of fresh grass in the cows' daily ration (0–94%) fed either indoors or via grazing (daytime grazing or continuous grazing). Six samples were from organic/biodynamic farms. PHY and PA concentrations were not significantly higher in organic/biodynamic compared with conventional milk, nor were they correlated with the amount of fresh grass in the diet. The SRR/RRR-diastereomers ratio was correlated with the percentage of fresh grass in the diet and was lower in organic milk than in conventional milk, although the difference was not significant (p = 0.057). These results indicate that PHY and PA contents are not suitable indicators of pasture grazing or organic/biodynamic farming, whereas the SRR/RRR-diastereomers ratio may be useful for indicating fresh grass feeding and organic farming.