Milk fatty acid stability during storage

Milk fat trans-10 C18:1 can be used in diagnosing low milk fat production on dairy farms as it is a specific marker of biohydrogenation induced milk fat depression. Individual fatty acids (FA), including the trans C18:1 isomer, can only be determined by GLC chromatography. The analysis is currently available at a limited number of labs and often requiring long-distance shipping. Expedited shipping with dry ice or ice packs is expensive. Therefore, the objective of this study was to determine the effect of heat treatment before shipping, shipping temperature, and shipping time on milk FA profile. Samples were collected from three farms on two occasions and stored in a Styrofoam cooler with an ice pack, at room temperature, or at 37°C for 1, 2, 3, and 7 d. There was very little effect of heating the sample before shipping, shipping temperature, or shipping time on any FA analyzed. Differences observed were of small magnitude and not of practical importance demonstrating that milk FA profile is expected to be very stable during shipping. Based on this, we propose that freezing samples and shipping in a sealed bag by second day shipment is appropriate and demonstrated that this had little effect on FA profile of 48 milk samples. Importantly, these methods are only recommended for GLC analysis of FA profile and freezing is not appropriate for shipping for analysis by mid-infrared spectrometry based methods or methods quantifying compounds per unit of milk as it is difficult to homogenize samples after freezing or extended shipping that results in denaturization of proteins and breaking of fat globules.