Bovine milk contains 2%–5% lipids, secreted by breast epithelial cells and dispersed in the milk in the form of milk fat globules. Most of the milk fat (about 98%) exists in the milk fat globules in the form of glycerolipids, and the rest (about 2%) is polar lipids, including glycerophospholipids, sphingolipids, glycolipids, mainly distributed in the milk fat globule membrane surface. Despite their relative scarcity, milk polar lipids play an indispensable role in the growth and development of mammals. This review introduces readers to the types of polar lipids in milk, and compares the types and quantities of milk polar lipids from different milk sources including cows, buffalo, yak, sheep, goats, donkeys, camels, and humans. Next, this review summarizes the physiological functions of milk polar lipids including inhibition of neutral fat absorption, regulation of intestinal microbial community composition, prevention of cardiovascular disease, prevention of non-alcoholic fatty liver, promotion of cognitive function and nervous system development, and anti-inflammatory effects with a view to providing reference for the research and development of functional milk fat products.

The secondary structure of whey proteins in donkey and bovine milk were investigated by Fourier transform infrared spectroscopy (FTIR), and comparative functional evaluation was carried out by gene ontology (GO) annotation and Kyoto Encyclopedia of Genes and Genomes (KEGG) pathway analysis. Results showed that there were differences in the secondary structure of whey proteins between donkey and bovine milk. As the lactation period proceeded, the secondary structure content of whey proteins in both milks changed. Whey proteins in donkey colostrum and milk were involved in more biological functions and metabolic pathways compared with those in bovine colostrum and milk, especially in donkey milk, which could thus be more beneficial to the development and utilization of infant formula milk powder.