In order to improve the flavor and quality of goat milk yogurt and enhance its functional value, Lactobacillus plantarum JS5 and JS19, isolated from Jiangshui, a traditional Chinese fermented vegetable food, were used for goat milk fermentation. The physicochemical properties, textural characteristics, and functional properties of goat milk yogurt were evaluated. The results showed that mixed-culture fermentations with each isolate and a commercial starter culture improved the water-holding capacity and apparent viscosity of goat milk yogurt, reduced its hardness and gumminess and promoted the release of acetaldehyde and diacetyl. The rate of cholesterol degradation (up to 36.62%) in goat milk yogurt containing Lactobacillus plantarum JS5 was significantly higher than that in the control group (P < 0.05). Goat milk yogurt containing Lactobacillus plantarum JS19 showed stronger antioxidant capacity in vitro, which could scavenge 70.58% of 1,1-diphenyl-2-picrylhydrazyl (DPPH) radical and had a ferric ion reducing antioxidant power (FRAP) value of 32.03 μmol ferrous sulfate equivalent/L on the first day of storage. Therefore, both strains are suitable for goat milk fermentation.

The protein composition and digestion characteristics of goats’ milk were studied using sodium dodecyl sulfate polyacrylamide gel electrophoresis (SDS-PAGE) and in vitro simulated digestion. The results showed that goats’ milk proteins mainly included casein (αS1-casein, αS2-casein, β-casein and κ-casein, accounting for 23.10%, 30.39%, 38.09% and 8.42% of the total casein, respectively) and whey protein (α-lactalbumin, β-lactoglobulin, lactoferrin, serum albumin and immunoglobulin, accounting for 24.59%, 57.50%, 4.35%, 8.69% and 4.88% of the total whey protein, respectively). Casein was mainly digested in the intestinal juice, and the digestibility reached more than 99.00% after 120 min in the gastric juice, while it only took 2 min to reach more than 99.00% digestibility in the intestinal juice. The digestibility of lactoferrin, serum albumin and immunoglobulin in the gastric juice and intestinal juice was significantly higher than that of α-lactalbumin and β-lactoglobulin (P < 0.05), and α-lactalbumin and β-lactoglobulin were not easy to digest in the gastric and intestinal juice. The digestibility of α-lactalbumin and β-lactoglobulin was 67.53% and 50.82% in the gastric juice at 120 min, and 58.16% and 64.04% in the intestinal juice at 30 min, respectively. Gastrointestinal juice digestion also showed that casein in goats’ milk was more digestible than whey protein in goats’ milk.

In order to obtain more data on proteins in goat milk, cow milk and human milk, their basic components were determined, and bioinformatic analysis of their proteins was performed by proteomics. The results showed that the protein contents of goat milk and cow milk were higher than that of human milk, while the contents of fat and lactose were higher in human milk. A total of 3 370 proteins were identified in the three kinds of milk, and gene ontology (GO) analysis of these proteins indicated that they were mainly involved in biological processes such as cell process and metabolism process, and distributed in the cell, organelles and extracellular region. Their molecular functions included binding and catalytic activity. The KEGG pathway varied in the three kinds of milk and was enriched in protein processing in the endoplasmic reticulum. In the protein-protein interactions network, the 307 shared proteins participated in several pathways such as carbon metabolism, glycolysis/gluconeogenesis, and amino acid biosynthesis.

The composition and digestion characteristics of proteins in donkeys’ milk and mares’ milk were investigated by sodium dodecyl sulfate polyacrylamide gel electropheresis (SDS-PAGE) analysis. The results showed that the digestibility of casein in donkeys’ milk and mares’ milk was 97.9% and 96.7% respectively after digestion in simulated gastric juice for 120 min, and was 98.6% and 97.7% respectively after digestion in simulated intestinal juice for 30 min. It took 30 min to almost completely digest proteins in both milks in simulated gastrointestinal juice, and mares’ milk proteins were easier to digest than donkeys’ milk proteins. Taken together, it was found that donkeys’ milk and mares’ milk proteins were mainly digested in simulated intestinal juice rather than simulated gastric juice and the latter was more digestible than the former.

Goat milk is nutritious and easy to absorb, but its odor restricts the development of goat milk products and the goat milk industry. This paper provides a review of the odorant compounds of goat milk and their sources. Three techniques for the deodorization of goat milk, physical and chemical treatments and microbial fermentation are described and suggestions for this area of research are proposed. We hope that this review will provide an innovative basis for developing a new technique to deodorize goat milk and for goat milk fermentation.