Donkey milk is considered as an ideal substitute for human milk because of its high contents of whey protein, lactose, lysozyme, unsaturated fatty acids and vitamin C, and low contents of casein and fat. Additionally, donkey milk has various physiological functions, including hypoallergenic, bacteriostatic and anticancer activity. Thus, this review introduces readers to the nutritional composition of donkey milk, including proteins, amino acids, fats, minerals, vitamins., and compares it with that of human milk, bovine milk, buffalo milk, goat milk, and camel milk, in order to provide useful information for the comprehensive processing and utilization of donkey milk.

The effects of Alcalase (AT), Protamex (PT) or Flavorzyme (FT) treatment on the antigenicity and molecular mass distribution of proteins, flavor and color of skim milk were investigated by using various techniques such as indirect competitive enzyme-linked immunosorbent assay (ic-ELISA) and Tricine-sodium dodecyl sulphate polyacrylamide gel electrophoresis (Tricine-SDS-PAGE). The results showed that the effect of AT treatment on reducing the antigenicity of the major milk allergens was significantly better than that of PT and FT treatment (P < 0.05). The antigenicity of α-lactalbumin (α-LA), β-lactoglobulin (β-LG) and casein (CN) was inhibited by 64.01%, 76.00% and 69.10% by AT treatment for 20 min at an enzyme/substrate ratio of 500 U/g, respectively. The amount of low molecular mass peptides in skim milk increased significantly after treatment with each of the three enzymes. The bitterness, astringency, aftertaste of bitterness (aftertaste-B) and aftertaste of astringency (aftertaste-A) increased with increasing enzymatic treatment time and with increasing enzyme/substrate ratio. The taste of FT-treated milk was better than that of AT- or PT-treated milk. The brightness value of milk decreased significantly, while the redness value increased significantly after enzymatic treatment (P < 0.05). The transmittance increased as well. The color of skim milk treated by AT was more similar to that of whole milk.

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.