Enhanced characterisation of milk fat globules by their size, shape and refractive index with scanning flow cytometry

We present a high-precision method for characterisation of a milk sample by the distributions over milk fat globules (MFG) size, shape, and refractive index (RI). We measured light-scattering profiles of individual MFGs and used global optimisation to retrieve their characteristics. We tested two optical models, a sphere and an oblate spheroid, and found that the latter is a more adequate model for part of the MFGs. We applied the developed method to samples of raw bovine milk and milk from two commercial manufacturers. Diameter and RI of individual MFGs were determined with median errors of 74 nm and 0.0094, respectively, which proves the method to be sensitive to small changes in the MFG properties. Moreover, the distributions over size, surface area, and RI showed a good sensitivity to the details of the milk treatment. In particular, the MFG specific surface area is significantly different for all three milk samples studied.