Phytanic acid concentrations and diastereomer ratios in milk fat during changes in the cow’s feed from concentrate to hay and back

摘要

The phytanic acid content in milk correlates with the amount of green items in the cows’ feed. For this reason, the four-fold methyl-branched fatty acid has been suggested as a potential marker for the authentication of organic milk. In this study, we attempted to provide further support for this idea by studying the progression of the phytanic acid level and diastereomer ratio in milk fat by transition of the diets from high proportions of concentrate (typical “conventional” feed) to hay (typical “organic” feed in winter) and back to “conventional” feed. Milk samples taken from three cows were analyzed on both the phytanic acid concentration and diastereomer distribution. The cows were initially fed with “conventional” feed (ground feed with high portions (30–45 %) of concentrate), then the feed was changed within 1 week to 100 % hay (“organic” feed), and after ~6 weeks, the feed of two cows was changed back to the initial feed with concentrate (phase Cb). During the “conventional” feeding at the beginning of the experiment, the phytanic acid concentration was low (100–130 mg/100 g milk fat). When the feed was changed to hay (“organic” feed), the phytanic acid concentration immediately increased to a stable level of about 160 mg/100 g lipids. Changing back the feed to “conventional” feed, the phytanic acid concentration dropped immediately back below the value measured in the initial phase. Likewise, the SRR/RRR-diastereomer distribution of phytanic acid in the milk was an excellent indicator for the changes in the cows’ feed. While the SRR/RRR-diastereomer ratio was 1.5 during “conventional” feeding, it immediately decreased to equal amounts of both diastereomers when hay was supplied as feed. Abandonment of concentrate in conventional feeding increased the phytanic acid content but the SRR-diastereomer was still dominant and thus the SRR/RRR-diastereomer ratio was different to organic milk. Our results indicate that both parameters, i.e., the phytanic acid content and SRR/RRR-diastereomer ratio need to be measured for authentication of organic milk.