Characterization of size and composition of milk fat globules from Sarda and Saanen dairy goats

The small size of goat milk fat globules (MFGs) is one of the factors contributing to the higher digestibility of goat milk compared to other milks. In this study, size, protein composition and lipid distribution of MFGs were evaluated comparatively in a popular dairy breed, Saanen, and in a minor breed, Sarda. MFGs were found to be significantly smaller in Sarda compared to Saanen goats, with average diameters of 2.73 ± 0.15 μm and 3.63 ± 0.27 μm, respectively. Raman spectroscopy revealed differences in the lipid profiles of differently sized MFGs within each breed, with MFGs of the same size class having comparable profiles between breeds. Proteomic characterization by SDS-PAGE followed by tandem mass spectrometry (GeLC-MS/MS) and label-free differential quantification highlighted significant differences in expression levels of MFG proteins from the two breeds, with a higher abundance of cytoplasmic proteins in Sarda MFGs and of membrane proteins in Saanen MFGs. Moreover, differences in the relative abundance of several major MFG proteins were observed for the two breeds. In conclusion, this study demonstrates the existence of breed-dependent differences in the lipid and protein makeup of goat MFGs, likely related to their different size distribution. This highlights once again the importance of investigating biodiversity in autochthonous and neglected breeds, which often possess valuable attributes that might be lost as a consequence of the widespread diffusion of highly productive, but more homogeneous, dairy breeds.