Donkey Milk Study: Proteomics Data of Greek Trading Milk (Proikakis 2021)

633 proteins were identified in six pasteurized donkey milk samples from three Greek regions. Only 19 of these were assigned to donkey or horse sequences; 505 are based on a single unique peptide.

The study in brief

• Original title: Proteomic data of donkey's milk
• Authors: Proikakis S.C., Bouroutzika E.V., Anagnostopoulos A.K. et al.
• Journal: Data in Brief, 39, 107507 (2021)
• Country: Greece · Study type: Laboratory study

How it was investigated

Data article without own animals: Six commercially available, pasteurized and deep-frozen donkey milk samples from three regions of Greece (Attica, Epirus, Macedonia; two samples each) were purchased from retail. After thawing, the samples were centrifuged and separated into fat, whey, and casein layers; the whey fraction was investigated (200 µg protein per batch, digestion with trypsin). The peptides were measured by nano-liquid chromatography with tandem mass spectrometry (bottom-up proteomics) in triplicate per sample and compared against tested protein databases for mammals and for the donkey (false discovery rate 1%, peptides at least 6 amino acids).

Important figures

• 633 – identified proteins or protein groups (Supplementary Table 1)
• 6 – commercially available samples from 3 regions, 3 measurements each
• 5 – proteins from the donkey database (e.g. β-Lactoglobulin 1 and 2, β-, αS1-, αS2-Casein)
• 14 – further proteins with horse sequence (e.g. α-Lactalbumin, Lactotransferrin, Lysozyme C)
• 233 – proteins that were assigned mouse sequences
• 141 – proteins that were assigned human sequences

Results

In the six samples, a total of 633 proteins or protein groups were identified. According to the article, 628 assignments come from the mammal database and 5 from the donkey database.

The five proteins identified via the donkey database are β-Lactoglobulin 1 and 2 as well as β-, αS1- and αS2-Casein. Horse sequences were identified for, among others, α-Lactalbumin A and B/C, Lactotransferrin, Serumalbumin, Lysozyme C (milk isoform), Clusterin and κ-Casein.

By number of spectra hits, β-Lactoglobulin 1 (346), β-Casein (219) and β-Lactoglobulin 2 (133) dominated. By summed peak area, 22.16% was attributed to β-Lactoglobulin 1 and together 23.36% to the two α-Lactalbumin entries.

Limitations of the study

• Many assignments via foreign species: Only 19 of the 633 entries were assigned donkey or horse sequences, the rest via mouse, human, rat, cow and other species. Whether it is the corresponding donkey protein in each case was not separately checked.
• Low detection depth: 505 proteins are based on a single unique peptide, 406 on only one spectra assignment, and 225 entries have a score of 0 in Supplementary Table 1. The total number of 633 should therefore be read as an upper limit.
• Method-related foreign proteins in the list: Supplementary Table 1 contains the pig trypsin used for cleavage (63 PSMs, sixth most frequent entry) as well as several human skin keratins, which usually come from sample preparation. They are included in the number 633.
• Whey or total protein?: According to the methods section, only the whey fraction was analyzed, but the list contains β-, αS1-, αS2- and κ-Casein, β-Casein even as the second most frequent entry. The separation of whey and casein by centrifugation was therefore incomplete; the abstract and data table speak generally of "proteins of donkey milk".
• Few retail samples, no quantities: Six pasteurized retail samples were investigated without information on animals, lactation stage or heating conditions. No concentrations were determined; PSMs and peak areas only allow rough relative comparisons.

Level of evidence: Basic research (laboratory) – describes properties of the milk, no statement about effects in humans.

Our assessment

The data article lists which proteins could be detected in six Greek retail samples of donkey milk. The classic milk proteins are well documented; for the majority of the remaining entries, the evidence base is narrow. Statements about quantities, nutritional value or effects cannot be derived from this.

Source: Proikakis S.C., Bouroutzika E.V., Anagnostopoulos A.K., Tsangaris G.Th. (2021). Proteomic data of donkey's milk. Data in Brief. DOI: 10.1016/j.dib.2021.107507 · Summarized by the DON DONKEY'S editorial team, as of: October 2026.

End of the study summary. The study was conducted independently by DON DONKEY'S® and does not refer to our products. Our donkey milk is a food.