A Comparison of Different Methodologies for the Measurement of Extracellular Vesicles and Milk-derived Particles in Raw Milk from Cows.

Cow's milk is economically important to the agricultural industry with the nutritive value of milk being routinely measured. This does not give full insight into normal mammary tissue turnover during the course of lactation, which could be important for both an understanding of milk production and animal welfare. We have previously demonstrated that submicron particles, including extracellular vesicles (EVs), can be measured in unprocessed cow's milk by flow cytometry and that they correlate with stage of lactation. A number of different techniques are available to measure EVs and other milk-derived particles. The purpose of this study was to compare two different methodologies and the value of fluorescent staining for the phospholipid phosphatidylserine (PS), which is exposed on the surface of EVs (but not other milk-derived particles). We used two different flow cytometers and nanotracker analysis to detect milk-derived particles in whole and skimmed milk samples. Our findings indicate significant correlation, after staining for PS, suggesting potential for larger multicenter studies in the future.