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.

In this study, the effect of dual-enzyme hydrolysis on the allergenicity of the major proteins in skimmed milk was evaluated based on the degree of hydrolysis, molecular mass distribution, immunoglobulin G (IgG) binding capacity and allergic patients’ serum IgE binding capacity of hydrolysates. The results showed that after one-step hydrolysis for 80 min at an enzyme/substrate ratio of 3 000 U/g and an Alcalase to Flavourzyme ratio of 3:1, the IgG binding capacity of casein, α-lactalbumin and β-lactoglobulinin in skimmed milk decreased significantly by 74.93%, 97.24% and 93.46%, respectively (P < 0.05).The advanced structure of proteins was damaged, leading to an increase in the α-helical and β-turn contents, and a decrease in the β-sheet content. In addition, the free sulfhydryl content increased significantly to 14.29 μmol/g (P < 0.05), the surface hydrophobicity also increased, and the structure became loose. The particles in skimmed milk were aggregated, causing the average particle size to increase significantly to 346.90 nm (P < 0.05) and reducing the stability of skimmed milk. The binding capacity to serum IgE from patients with milk allergy of the enzymatic hydrolysate decreased significantly by 23.53% (P < 0.05), and the overall allergenicity decreased significantly by 69.60% (P < 0.05). Therefore, dual-enzyme hydrolysis is an effective method to reduce the allergenicity of skimmed 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 is considered as the raw milk of choice for the production of infant formula. Amino acids in bovine milk, the structural units that make up milk proteins are classified into two groups: free and insoluble-proteome amino acids, which are distributed in different regions (structural domains). In this experiment, we collected bovine colostrum at 0–7 days postpartum and mature milk at 15 days-6 months postpartum for comparative analysis of the insoluble-proteome and free amino acids in them. The results indicated that 9 essential free amino acids and 7 non-essential free amino acids were detected in both milks. Additionally, another non-essential free amino acid was found in bovine colostrum. Among these, 8 essential and 4 non-essential amino acids were found to be significantly more abundant in bovine colostrum than in mature milk (P < 0.05). Among the insoluble-proteome amino acids, 8 essential amino acids and 10 non-essential amino acids were detected simultaneously in both milks. Moreover, the levels of threonine, arginine, serine, cysteine, alanine in bovine colostrum were significantly higher than in mature milk (P < 0.05), while the level of lysine was significantly lower than in mature milk (P < 0.05).

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.

Biological preservatives of lactic acid bacteria (LAB) have been gradually applied to food preservation because of their excellent properties such as naturality, antibacterial activity, safety and reliability. The screening of Lactobacillus plantarum with superior fermentation ability and antifungal activity is important for the production and preservation of fermented milk. In this research 33 strains of L. plantarum with potential antifungal properties were used as starters to ferment skim milk. Variations in mold and yeast counts and post-acidification during storage at room temperature under open conditions and mixed-culture fermentation properties were assessed to select L. plantarum with superior preservation properties. The results indicated that 9 selected strains of L. plantarum from initial screening had obvious antifungal activity. The variation of acidity of milk fermented by L. plantarum IMAU80091 and IMAU80106 was significantly lower than that of milk fermented by other strains and commercial preservative bacteria (P < 0.05). Moreover, milk fermented with mixed cultures (1:1) of L. plantarum IMAU80091 and IMAU80106 showed great inhibitory activity against yeasts than did commercial preservative bacteria significantly (P < 0.05). After storage for 21 d, the titratable acidity was (138.24 ± 1.19) °T, which was significantly lower (P < 0.05) than that of milk fermented by commercial preservative bacteria (146.41 ± 1.18) °T. In summary, mixed cultures of L. plantarum IMAU80091 and IMAU80106 possess superior antifungal properties as a promising biopreservative and could prevent fungal contamination effectively.