The capacity of mammals to produce milk, which provides nutrition as well as immune protection to the offspring, distinguishes them from other animals. While milk proteins have been researched for decades, developments in modern proteomics and bioinformatics allow us to examine the complexity of the milk matrix with more sensitivity. We can effectively identify and quantify bioactive proteins, enzymes, and nutritional proteins in milk that are essential to the early growth of various mammal species. Bovine milk dominates the milk and dairy markets due to the volumes of production. However, camel milk typically commands a higher price point, and it is increasing in production and popularity in Australia where its production is well suited to arid climates. Camel milk has known nutritional differences to cow milk, and the relative abundance of proteins with antimicrobial, immunomodulatory, and allergenic effects is of interest to consumers and the growing camel milk industry. This study compares a variety of sample preparation methods combined with liquid chromatography-tandem mass spectrometry and novel bioinformatics approaches to detect and quantify bioactive and allergenic proteins in camel milk.
Unpasteurised milk was analysed by filter aided sample preparation using two detergents, sodium deoxycholate or sodium dodecyl sulphate, at varying concentrations and both with and without fractionation by centrifugation. In total, 1256 protein groups were discovered and measured, with cream, whole, and skim milk containing 1075, 365, and 144 proteins, respectively. The largest number of proteins were detected in the cream fraction enriched with 5% sodium deoxycholate. Caseins dominate the camel milk proteome, with αs1-, αs2-, β- and κ-caseins present in different ratios. Major whey proteins present include α-lactalbumin and immunoglobulins. Proteins with known antimicrobial and immunomodulatory roles such as lactoferrin and lactoperoxidase were also seen in camel milk. Relative abundance of proteins with known bioactive domains, and allergenic epitopes are presented. This research informs our understanding of the camel milk proteome and its value as a food product and furthers our understanding of milk's involvement in neonatal development and immune protection. In the future, this methodological understanding will open the way for proteomic analysis of milk from further species to find antimicrobial and bioactive proteins unique to those species.