Researchers compare cow and camel milk proteomes, focusing on immune proteins and processing

Immune proteins dominate cream fractions, with camel milk containing 49 and cow milk 47, surpassing whole and skimmed milk

Study: Beyond nutrition: Exploring immune proteins, bioactive peptides, and allergens in cow and Arabian camel milk. Image Credit: photos_adil/Shutterstock.com

In a recent study published in Food Chemistry, researchers compared cow and camel milk proteomes, focusing on immune proteins, bioactive peptides (BPs), and allergens. They also evaluated the impact of fractionation and processing methods.

Background

Milk, a hallmark of mammals, provides nutrition and immunological protection through its balanced composition of proteins, fats, and lactose. Beyond sustenance, milk proteins and BPs play therapeutic roles, including antimicrobial, antihypertensive, and antioxidant effects.

Camel milk, which is gaining popularity due to its perceived health benefits, differs significantly from cow milk in composition and allergenicity. It notably lacks β-lactoglobulin (β-Lg), a major allergen in cow milk. However, milk proteins can trigger immunoglobin-E (IgE) —mediated allergic responses.

Further research is needed to explore immune-related functions, therapeutic potentials, and allergenic risks of milk proteins and peptides to ensure safe and beneficial consumption.

About the study

Commercially pooled raw cow milk (Cleopatra's Bath Milk, New South Wales, Australia) and Arabian camel milk (Good Earth Dairy, Western Australia, Australia) were analyzed through four technical repeats. Milk samples were separated into skimmed and cream portions via centrifugation. The cream fraction was washed with phosphate buffer solution and treated with 0.4% sodium dodecyl sulfate (SDS) to solubilize hydrophobic proteins, followed by vortexing, sonication, and fat separation. Skimmed milk was used as a benchmark for SDS treatment.

Protein concentrations were measured using the Bradford assay. Proteins were reduced, alkylated, and digested with trypsin for peptide analysis using SWATH-MS and DIA-NN, employing FASTA reference proteomes for Bos taurus and Camelus dromedarius. Native peptides were purified via Solid Phase Extraction (SPE) and analyzed with IDA mass spectrometry. Bioactive proteins (BPs) and allergens were mapped using a custom database and AllerCatPro.

Data were visualized with R, Cytoscape, and Circos plots to identify immune proteins, potential allergens, and bioactivities. Statistical analyses included KEGG pathway enrichment and differential protein abundance testing to compare cow and camel milk proteomes.

Study results

In the present comparative analysis of camel and cow milk, the highest number of protein groups was identified in the cream fraction of both species, with camel milk yielding 537 distinct proteins and cow milk 560. These findings highlighted the protein diversity within the cream fraction.

Overlapping protein groups were observed across all milk fractions, with camel milk showing greater overlap between cream and whole milk (579 proteins) than between cream and skimmed milk (438 proteins). Similarly, cow milk exhibited a higher overlap between cream and whole milk (271 proteins) compared to cream and skimmed milk (241 proteins). This indicated the effectiveness of SDS treatment in solubilizing cream-associated proteins, particularly in camel milk.

Immune system-related proteins were more abundant in the cream fraction for both camel and cow milk. Camel cream contained 49 immune-related proteins, while cow cream had 47, significantly higher than whole or skimmed milk fractions.

Statistical analysis using the Kruskal-Wallis test confirmed significant differences in immune protein abundance between cream and other milk fractions. In contrast, no significant differences were observed between skimmed and whole milk. Notably, immune-related pathways, including antigen processing and endocytosis, were enriched in cream, particularly in camel milk.

Differential protein abundance analysis revealed that camel cream exhibited upregulation of 307 proteins compared to whole milk and 189 proteins compared to skimmed milk. These proteins were predominantly associated with immune pathways, such as antigen presentation and ribosome function.

Cow cream also showed significant upregulation of proteins involved in immune processes, including Fc gamma receptor-mediated phagocytosis and leukocyte migration. Protein-protein interaction (PPI) network analysis identified key immune proteins, such as integrin β2 and complement C3 in camel milk and integrin β2 and heat shock protein 90 in cow milk, as central nodes critical for network stability.

The study also highlighted differences in BP enrichment between camel and cow milk. Camel milk demonstrated greater BP diversity, with the filtration method yielding 888 native peptides, compared to 223 in cow milk. Predicted bioactivities included antihypertensive, antimicrobial, antioxidant, and antidiabetic properties. Camel milk also exhibited a higher number of tryptic peptides with potential bioactivity compared to cow milk.

In allergenicity profiling, camel and cow milk contained 53 and 52 potentially allergenic proteins, respectively. High overlap was observed between the allergen profiles of the two species, with 32 cow milk allergens having orthologous counterparts in camel milk. Notably, β-Lg, a major allergen in cow milk, was absent in camel milk, underscoring its lower allergenic potential.

Conclusions

To summarize, the cream fraction showed the highest protein recovery, with camel milk exhibiting greater proteomic diversity and BP abundance. Key immune proteins, including integrin β2 and heat shock proteins, were enriched in cream, emphasizing its role in immune-related pathways.

Camel milk displayed a higher capacity for BP generation and lacked β-Lg, a major cow milk allergen, supporting its hypoallergenic potential. These findings highlight camel milk's therapeutic properties and the importance of fractionation for studying milk proteins.