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Research on donkey milk · Study 119
Ultrasound, heat and rennet coagulation in a milk comparison
Cow’s, goat’s, buffalo and donkey milk were treated with ultrasound (200–1000 W) or heat (65–100 °C). In donkey milk, the β-sheet share of the proteins rose from 43.89 % to up to 48.33 %; its rennet gel was too weak for a texture measurement.
At a glance · swipe or use the arrows
The key figures
Study design
How it was studied
Raw milk from cows, goats, buffalo and donkeys from one farm each in China (donkey milk from Liaocheng, Shandong) was transported chilled and stored at −80 °C until examination. Three batches were formed per type of milk: untreated control, ultrasound treatment in an ultrasonic bath (20 min at 200, 400, 600, 800 or 1000 W, water temperature 20 ± 2 °C) and heat treatment in a water bath (65 °C/30 min, 80 °C/30 min, 90 °C/15 min, 100 °C/15 min). Turbidity, particle size of proteins and fat globules, zeta potential, protein secondary structure (FTIR, amide I band), intrinsic fluorescence and surface hydrophobicity were measured. The milk was then coagulated at pH 5.9 and 38 °C with rennet (chymosin) and calcium chloride for 45 min; water-holding capacity, texture and rheology (storage and loss modulus) were determined on the gel. All measurements were made in triplicate and analysed with one-way ANOVA and Duncan’s test.
Interactive chart · values from the study
Protein secondary structure of donkey milk after treatment
Means (n = 3) from Table 1 (control, ultrasound) and Table 2 (heat). The control values differ slightly between the two tables (β-turn 19.04 ± 0.12 and ± 0.13; random coil 14.49 and 14.47).
Second analysis
Donkey milk: secondary structure by ultrasound level
Means (n = 3) from Table 1; significant differences from the control only at 400 and 600 W. 20 minutes of treatment in the ultrasonic bath in each case.
Results
What the study measured
Untreated, donkey milk showed the lowest turbidity, the lowest absolute zeta potential, the lowest intrinsic fluorescence and the lowest surface hydrophobicity of the four types of milk, but the largest protein particles (287 ± 2.1; unit not given). The authors attributed this to the composition of the caseins in donkey milk.
In donkey milk, turbidity rose significantly after heat treatment from 80 °C/30 min; the protein particles became larger after 80 °C/30 min and 100 °C/15 min (maximum 371 ± 7.2). The size distribution of the fat globules in donkey milk hardly changed with either treatment, whereas cow’s and goat’s milk showed a bimodal distribution after 100 °C/15 min.
Ultrasound at 400 and 600 W increased the β-sheet share in donkey milk (43.89 % to 48.17 % and 48.33 % respectively) and lowered α-helix (to 21.18 % and 21.01 %) and β-turn (to 17.39 % and 17.38 %); at 800 and 1000 W the values were close to the control again. After heat treatment, α-helix and random coil shares fell slightly, and the β-sheet share rose at 65 °C and 100 °C to 45.43 % and 45.69 % respectively.
The zeta potential of donkey milk increased significantly after ultrasound at 200–400 W and after heat treatment; intrinsic fluorescence rose markedly after 90–100 °C for 15 min. Surface hydrophobicity peaked at 200 W with ultrasound and rose with heat intensity.
The water-holding capacity of the rennet gels increased significantly with treatment intensity in all four types of milk; donkey milk consistently had the lowest and buffalo milk the highest (control 26.51 %, after 800 W 39.89 %, after 100 °C/15 min 86.96 %). Specific values for donkey milk are shown only graphically.
Because of the weak gel formation, hardness, springiness and cohesiveness of the donkey milk rennet gel could not be measured. In rheology, storage and loss modulus of the gels from donkey and buffalo milk were below those from cow’s and goat’s milk; in donkey, cow’s and goat’s milk, the storage modulus fell with increasing heat intensity.
Authors’ conclusion: In the view of Hou et al. (2024), ultrasound and heat treatment changed turbidity, particle size, zeta potential, protein structure and gel properties differently depending on the type of milk; the water-holding capacity of the rennet gels rose with treatment intensity in all four types of milk. The authors saw this as a basis for technologically controlling gel properties in cheesemaking. According to their description, gel formation remained weak for donkey milk.
Critical assessment
Strengths and limitations
The milk for each type came from a single farm; number of animals, breed, lactation stage and whether individual or pooled samples were used are not stated. The three replicates are parallel batches of the same milk. In addition, the milk was frozen at −80 °C before treatment, which may already change protein structure and fat globules.
For donkey milk, numerical values are given only for secondary structure (Tables 1 and 2) and two particle sizes; turbidity, zeta potential, water-holding capacity and rheology are shown only as figures. The unit is missing for the particle sizes, and the formula for water-holding capacity is not printed in the text.
The untreated controls should be identical in Tables 1 and 2 but differ: donkey milk β-turn 19.04 ± 0.12 vs. ± 0.13 and random coil 14.49 vs. 14.47 %, buffalo milk β-turn 18.99 vs. 17.99 %. The cohesiveness of the buffalo milk gels (6.52–9.49) is an order of magnitude above the values for cow’s and goat’s milk (0.12–0.38), suggesting a unit or transcription error.
The abstract mentions a heat level of 63 °C/30 min, the methods 65 °C; the rheology section describes a maximum at “83 °C for 30 min”, a level that did not exist. The conclusion speaks of increased moduli due to the treatments, whereas the results section speaks of moduli falling with higher intensity – the differences mainly concern the types of milk relative to one another.
Treatment took place in an ultrasonic bath with three samples side by side; only the nominal power of the device is given. The energy actually delivered into the milk was not determined, which makes comparison with other studies difficult.
All four types of milk were examined with the same treatment levels and measurement methods. The secondary structure and texture data are documented in tables with standard deviations and significance letters.
Editorial assessment: The study is a food technology laboratory investigation of rennet coagulation. It describes how protein structure and gel formation change under defined laboratory conditions; no statements about nutritional value, effects or the treatment of milk at home can be derived from it. To the research archive.
Research question for DON DONKEY’S®
Can a measurable rennet gel be obtained with donkey milk – alone or mixed with other types of milk – and how does the result depend on the lactation stage and protein content of the milk of individual jennies?
Original publication
Impact of ultrasonic and heat treatments on the physicochemical properties and rennet-induced coagulation characteristics of milk from various species
Original title of the publication.
Hou W., Ma X., Yu Z., Bari L., Jiang H., Du Q., Fan R., Wang J., Yang Y., Han R.
Ultrasonics Sonochemistry · 2024 · 111, 107084
College of Food Science and Engineering, Haidu College and Bathurst Future Agri-Tech Institute, Qingdao Agricultural University, Qingdao/Laiyang, China; Food & Agriculture Research Division, Center for Advanced Research in Sciences, University of Dhaka, Bangladesh; a testing and certification company in Qingdao, China
10.1016/j.ultsonch.2024.107084: 10.1016/j.ultsonch.2024.107084
Transparency: National Key R&D Program of China (2022YFD1301005), Shandong Province Natural Science Foundation (ZR2022MC184), Shandong Provincial Key Research and Development Program (2021TZXD004) and High-level Talents Foundation of Qingdao Agricultural University (665/1220003). The authors declare no competing financial interests or personal relationships that could have influenced the work. No product-related statement for DON DONKEY’S®.
Summarised and reviewed by the DON DONKEY’S editorial team on the basis of the original publication · as of October 2026
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.
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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.
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