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What remains of milk protein when it is digested in a test tube? A Turkish laboratory study subjected casein and whey from donkey and camel milk to simulated digestion. The resulting protein fragments then underwent five chemical laboratory tests. The result: The fragments from casein performed better in several tests than those from whey – although there were some gaps and contradictions in the paper.
Laboratory study (in vitro) with chemical and enzymatic tests in a test tube – no statement about an effect in humans. Donkey milk is a food.
Study profile
| Feature | Information |
|---|---|
| Original title | An evaluation of the in vitro antioxidant and antidiabetic potentials of camel and donkey milk peptides released from casein and whey proteins |
| Authors | Akan E. |
| Journal | Journal of Food Science and Technology, 58(10): 3743–3751 |
| Year | 2021 (online since October 2020) |
| Country | Turkey |
| Study type | Laboratory study (in vitro), static simulated digestion |
| Sample | Donkey and camel milk from one farm each; 2 experimental approaches with 3 measurements each; number of animals not stated |
| DOI | 10.1007/s13197-020-04832-5 |
What question did the researchers ask?
Milk protein consists roughly of two groups: casein and whey proteins. During digestion, enzymes break both down into short chains of amino acids, so-called peptides. The author wanted to know how the peptide mixtures from donkey and camel milk behaved in chemical laboratory tests. Three radical tests (DPPH, ABTS, CUPRAC) and the inhibition of two enzymes (DPP-IV and α-glucosidase) in a test tube were measured.
How it was investigated
- Defatting: The milk was centrifuged (3,000 × g, 4 °C, 30 minutes), and the fat was separated.
- Separation: At pH 4.6, the casein precipitated; the supernatant was the whey. This created four samples: donkey casein, donkey whey, camel casein, camel whey.
- Digestion: Static simulated digestion according to a standard protocol with pepsin and pancreatin. Amylase was omitted because it was only about protein.
- Measurement: Degree of hydrolysis (proportion of broken bonds), peptide amount, HPLC profile, and five laboratory tests. Two experimental approaches, each measured three times.
The results
The whey samples were broken down more than the casein samples. The highest peptide amount was still found in the digested donkey casein. The values from Table 1 of the paper (mean ± standard deviation):
| Sample | Peptide concentration (mg/mL) | Degree of hydrolysis (%) |
|---|---|---|
| Camel whey | 4.26 ± 0.17 | 75.68 ± 2.70 |
| Camel casein | 3.37 ± 0.07 | 53.06 ± 3.98 |
| Donkey whey | 3.90 ± 0.45 | 73.41 ± 4.74 |
| Donkey casein | 4.94 ± 0.06 | 50.25 ± 1.04 |
In the laboratory tests, digested donkey casein came out on top in the DPPH test (IC50 262.84 µg/mL; IC50 is the concentration at which a test is inhibited by half – smaller means stronger in a test tube). Donkey whey came last in this test (IC50 570 µg/mL). In the ABTS and CUPRAC tests, camel casein achieved the highest values. In the inhibition of the enzyme DPP-IV, the casein samples were twice as high as the whey samples according to the text; for donkey casein, the paper lists an IC50 of 113.45 µg/mL. For α-glucosidase, donkey casein achieved an IC50 of 12.52 µg/mL. Many other individual values are only in figures or are marked as "data not shown".
In a test tube, the peptide mixtures from casein showed higher values in several chemical tests than those from whey. These are laboratory measurements, not statements about processes in the body.
Critical assessment
- Unknown samples: The number of animals, breeds, and the number of milk samples are not stated. The milk comes from a single farm for each animal type.
- Contradictions: For α-glucosidase in the whey samples, the text says "not determined", but in the same paragraph, values of 32.84 and 89.38 % are given. In the results section, donkey casein is considered the strongest DPP-IV inhibitor, while in the conclusion, it is camel casein.
- Hidden data: Several core values are only available as figures. The concentrations of the samples in the tests are missing.
- Sparse methodology: For digestion, the paper only refers to a standard protocol; pH values and times are not in the text. Which peptides were formed was not determined.
- Only test tube: Radical tests and isolated enzymes say nothing about what happens in the body. The author herself calls for further studies.
Funding, conflicts of interest, and level of evidence
According to the paper, the work was not funded by any public, commercial, or non-profit organization. The author declares no conflicts of interest. A correction to the article was published in 2021.
Level of evidence: Basic research in a test tube (in vitro) – describes properties of peptide mixtures in chemical tests, no statement about effects.
What does that mean for donkey milk as a food?
The study describes that during the simulated digestion of donkey milk protein, peptide mixtures are formed whose chemical behavior differs between casein and whey. The author interprets the enzyme tests in connection with type 2 diabetes. This was not investigated and cannot be derived from laboratory tests – we do not adopt this interpretation.
Our research question: Which peptides exactly are formed from donkey casein – and do other research groups with more milk samples and openly described conditions come to similar rankings?
Frequently asked questions
What is simulated digestion?
A laboratory procedure in which protein is treated sequentially with digestive enzymes such as pepsin and pancreatin. It replicates individual steps of digestion in a test tube, but not the processes in the body.
What does the degree of hydrolysis mean?
It indicates what proportion of the bonds in the protein was broken. In this study, it was 73.41 % for donkey whey and 50.25 % for donkey casein.
Was donkey milk tested on humans?
No. There were no trials with humans, animals, or cells – only chemical and enzymatic tests in a test tube.
You can find all measurements, interactive graphics, and the complete critical assessment on our research page: Study 78: Peptides from digested donkey and camel milk. Further studies in the research archive.
Akan E. (2021). An evaluation of the in vitro antioxidant and antidiabetic potentials of camel and donkey milk peptides released from casein and whey proteins. Journal of Food Science and Technology, 58(10), 3743–3751. DOI: 10.1007/s13197-020-04832-5
Summarized and checked by the DON DONKEY'S editorial team using the original publication · As of: October 2026. This summary does not replace the original work.
End of the study summary. The study was conducted independently of DON DONKEY'S® and does not refer to our products. Our donkey milk is a food.
