Lipidomics Reveals Differences in Lipid Composition Between Lipid Droplets and Milk Fat Globules in Dairy Goat Mammary Tissue

Milk fat globules (MFGs) are derived from lipid droplets (LDs) in the mammary epithelial cells of ruminants and released into milk. This study aimed to detect the differences in LDs and MFGs to reveal the mechanism by which LDs transform into MFGs in the mammary cells of dairy goats. The mammary gland tissue and milk of lactating dairy goats were collected and analyzed using lipidomics. The results showed that a total of 1167 and 675 lipid molecules were detected in the LDs and MFGs, respectively. The top four lipids in terms of their contents in the LDs were triglycerides (TGs), phosphatidylethanolamine (PE), phosphatidylcholine (PC), and diglycerol (DG), whereas the top four in the MFGs were TG, PE, PC, and phosphatidylinositol (PI). Furthermore, compared to the LDs, the contents of TG and DG in the MFGs were significantly increased (p < 0.05), while PC content was significantly decreased (p < 0.05). We also found that diglycerol (16:0:18), diglycerol (O-19:0:16), triglycerides (14:0:0_16:0), and phosphatidylethanolamine (P-15:0:20:3) were the key characteristic lipids in the transformation of LDs into MFGs. This study reveals the unique lipid profiles of LDs and MFGs and provides a theoretical basis for understanding the mechanism behind low-fat milk syndrome.