Donkey milk research · Study 150

Donkey milk fermented with lactic acid bacteria: lab values compared

In a laboratory experiment by a research group from Bari, the total phenolic content of donkey milk rose with fermentation by each of the 6 selected bacterial strains, with Lc. casei BGP93 from 0.279 to 0.543 mg GAE/g. Three strains reached a radical scavenging activity close to 50% in the DPPH test, and only Lp. plantarum LPAL inhibited Listeria monocytogenes – completely in fermented donkey milk, partially in cow and goat milk.

Important: A laboratory study using milk extracts, cell lines and a plate test. It does not examine what happens in the body when fermented donkey milk is consumed and does not show any health effect.

At a glance · swipe or use the arrows

The key figures

15strains of lactic acid bacteria and bifidobacteria tested

6strains selected: pH below 3.6 in all three milks

24 hfermentation at 30 °C, starting density 7 log10 CFU/mL

70 °Cpasteurisation of the milk for 2 minutes before fermentation

7.13pH of donkey milk on arrival (cow 6.6, goat 6.48)

0.279mg GAE/g phenolic content of unfermented donkey milk

0.543mg GAE/g phenolic content of donkey milk with Lc. casei BGP93

≈ 50%DPPH radical scavenging with BGP93, LC4P1 and ATCC23272

2human intestinal cell lines: Caco-2 and HCEC-1CT

1 of 6strains inhibited Listeria: Lp. plantarum LPAL

Study design

How it was studied

Laboratory study at the University of Bari (Italy): cow milk (control), goat milk from the Garganica breed and donkey milk from the Martina Franca breed, from farms in Apulia, were pasteurised (70 °C, 2 minutes), frozen and then fermented with bacterial strains. 15 strains of lactic acid bacteria and bifidobacteria were tested for acidification (24 h, 30 °C); 6 strains reaching pH below 3.6 in all milks were studied further. Total phenolic content (Folin–Ciocalteu), radical scavenging activity (DPPH), cell viability (calcein-AM) and reactive oxygen species (ROS) in the Caco-2 and HCEC-1CT cell lines with and without artificial oxidative stress (tBHP) were measured, as well as inhibition of Listeria monocytogenes in an agar test. Cow and donkey milk were bulk milk; the number of animals and replicates is not stated in the material.

Laboratory study

Study typeLaboratory study (in vitro)CountryItalyYear2025JournalAntioxidants (Basel)

Interactive chart · values from the study

Total phenolic content of unfermented milk and fermented donkey milk

Source: section 3.2 of the study (Folin–Ciocalteu method, mg gallic acid equivalents per g extract).

Results

What the study measured

Of 15 strains tested, 6 acidified all three milks to a pH below 3.6 within 24 hours: Lc. casei BGP93 and LC4P1, Lp. plantarum 8VEG3C, LPAL and ONI3, and Ls. reuteri ATCC23272. Lactic acid bacteria generally acidified more strongly than bifidobacteria.

Unfermented, donkey milk had the lowest total phenolic content (0.279 ± 0.006 mg GAE/g; cow 0.409, goat 0.363). After fermentation it rose significantly in donkey milk with all 6 strains, roughly doubling with Lc. casei BGP93 (0.543 ± 0.03 mg GAE/g). In cow and goat milk it stayed the same or partly decreased.

In the DPPH test, unfermented donkey milk showed the highest radical scavenging activity of the three milks. After fermentation it rose in all samples except donkey milk with Lp. plantarum LPAL; BGP93, LC4P1 and ATCC23272 reached values close to 50% regardless of milk type.

None of the samples significantly reduced the viability of Caco-2 cells. In HCEC-1CT cells there was a slight decrease with BGP93-fermented goat and cow milk.

Under artificial oxidative stress (tBHP), the milk samples significantly lowered the ROS content of the cells, most clearly goat and donkey milk. In HCEC-1CT cells, ROS levels were lowest with goat milk, followed by donkey and cow milk.

Unfermented milk did not inhibit Listeria monocytogenes. Only Lp. plantarum LPAL inhibited the bacterium in the agar test – completely in fermented donkey milk, partially in cow and goat milk.

Authors’ conclusion: Fermentation with selected lactic acid bacteria improves the functional properties of cow, goat and donkey milk depending on strain and milk type; the combinations Lc. casei BGP93 with donkey milk and Lp. plantarum LPAL with donkey milk appear particularly promising. What the study does not show: extracts were measured in the test tube and on cell lines – no effect after consumption and no shelf stability of a product.

Critical appraisal

Strengths and limitations

Test tube and cell linesClear limitation

Phenolic content, the DPPH test and ROS in cell cultures describe chemical and cellular reactions. What reaches the gut after consumption was not studied.

Artificial stress, tumour cell lineNote

Oxidative stress was induced with tBHP, and Caco-2 are tumour cells. The authors themselves report that the two cell lines responded differently.

One milk sample per speciesClear limitation

Cow and donkey milk were bulk milk from Apulia, one breed per species. Number of animals, lactation stage and number of replicates are not stated in the material.

Evaluative wordingNote

Terms such as “functional food” and “preventive nutrition” come from the authors. They go beyond the measured lab values; conflicts of interest are not stated in the material.

Broad strain screeningStrength

15 strains in three milks under identical conditions, plus several assays, show how strongly results depend on the combination of strain and milk.

clear limitationnotestrength

Editorial note: The paper shows that donkey milk behaves differently from cow and goat milk when fermented in the lab, especially in phenolic content and in the Listeria test with a single strain. This is a technological finding about combinations of milk and bacterial strain. It allows no statement on health effects of fermented donkey milk. To the research archive.

Research question for DON DONKEY’S®

How do pH, phenolic content and radical scavenging activity change when thawed donkey milk from our batches is fermented with a defined lactic acid bacterial strain – and how long do the values remain stable in chilled storage?

Laboratory studyFermentationLactic acid bacteria

Original publication

Comparative Evaluation of Functional Properties of Cow, Goat, and Donkey Milks Fermented with Lactic Acid Bacteria

Original title: Comparative Evaluation of Functional Properties of Cow, Goat, and Donkey Milks Fermented with Lactic Acid Bacteria

Caponio G. R., Annunziato A., Vacca M., Cavaliere M., Ceglie I., Ranieri M., Di Luca A., D'Alessandro A. G., Tamma G., De Angelis M.
Antioxidants · 2025 · 14(11), 1331

Department of Bioscience, Biotechnology and Environment and Department of Soil, Plant and Food Sciences, University of Bari Aldo Moro, Italy (according to the paper)

DOI: 10.3390/antiox14111331

Transparency: according to the paper, funded by Italy’s National Recovery and Resilience Plan (Agritech and OnFoods projects) and PSR Puglia 2014–2022. Conflicts of interest are not included in the available material. No product-related statement for DON DONKEY’S®.

Summarised and checked by the DON DONKEY’S editorial team against the original publication · As of: November 2026

End of the study summary

Note on our products

The study summarised above was carried out independently of DON DONKEY’S® and does not relate to our products. It serves solely to inform about the state of research.

DON DONKEY’S® donkey milk and donkey milk powder are foods. They are not intended to prevent, treat or cure any disease and do not replace medical advice.

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DON DONKEY’S® donkey milk

100 % donkey milk · raw milk, frozen

On this page we report the findings of a published study. Independently of that, you will find our donkey milk here: 100 % donkey milk, frozen as raw milk.

Transparency: The study examined milk from another herd – not the milk from our partner farms.

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Donkey Milk Powder

Donkey milk in powder form

For anyone who prefers a longer shelf life: our donkey milk in powder form – easy to store and portion.

Transparency: The study did not examine our donkey milk powder.