Buyer protection
Research on donkey milk · Study 19
Thermised donkey milk, lysozyme & intestinal barrier
In 2019, Yvon et al. examined how different heat treatments of donkey milk relate to microbiological parameters and enzymatic lysozyme activity – and whether thermised milk still shows comparable findings in a mouse model of stress-related intestinal barrier disorders.
The research question
Can heat reduce microorganisms without largely losing lysozyme activity?
The research group analysed raw milk samples from 15 French donkey milk farms. Microbiological indicators as well as lysozyme concentration and enzymatic lysozyme activity were examined.
The authors then compared several time–temperature combinations. The aim was a compromise between microbiological quality and preserving enzyme activity.
The second part tested whether the selected thermised milk still showed biological effects in a mouse model of stress-related intestinal barrier disorders.
Study design
From raw milk to the stress model
15 farms
Raw milk samples from various French donkey milk farms were analysed.
Heat
Several time–temperature combinations were compared.
Lysozyme
Concentration and enzymatic activity were considered separately.
Gut barrier
Raw milk and thermised milk were then examined in a stress mouse model.
Processing
72 °C for 2 minutes
The authors compared different heat treatments, including several time steps at 72 °C and a stronger treatment at 80 °C.
Among the conditions examined, 72 °C for 2 minutes was selected as the preferred compromise between microbiological reduction and preservation of lysozyme activity.
This is a study-specific choice of procedure. It is not a general safety or shelf-life guarantee for any donkey milk.
Time & temperature
Not every heat treatment is biologically the same.
Raw milk
Reference for microbiological parameters, lysozyme concentration and enzymatic activity.
72 °C / 2 min
Among the conditions tested, the authors identified this treatment as a suitable compromise between microbiological reduction and preservation of lysozyme activity.
Study conditionHeat & time
The study shows why the specific process conditions for bioactive milk proteins need to be documented precisely.
One of the key findings
Lysozyme amount is not the same as lysozyme activity.
An analytical measurement can show how much lysozyme is present. But it does not automatically follow how active the enzyme is in the respective test system.
Concentration
Concentration describes the analytically determined amount of lysozyme, expressed for example as mass per volume.
Enzyme activity
Activity describes how effectively the enzyme present works under the conditions of the activity assay used.
The animal model
Water avoidance
stress
In the biological part of the study, mice were repeatedly exposed to so-called water avoidance stress.
The animals were placed daily for a limited time on a small platform above water. The protocol was used to induce stress-related changes in the intestinal barrier experimentally.
The researchers then compared the findings with untreated and thermised donkey milk.
Key results
What Study 19 actually showed
Microbiological analysis
According to the authors, the raw milk samples examined had low mesophilic counts, and no pathogens were detected in the sample set reported. This is not a general safety guarantee for raw milk.
72 °C / 2 minutes
Among the conditions tested, this treatment was selected as a suitable compromise between reducing the microbial load and preserving lysozyme activity.
Concentration ≠ activity
In the farm samples examined, there was practically no linear correlation between lysozyme concentration and enzymatic activity.
Stress-related hyperpermeability
In the mouse model, both untreated and thermised donkey milk were associated with an attenuation of the stress-related increase in intestinal permeability.
Lipocalin-2
Faecal lipocalin-2 was examined as a marker of low-grade intestinal inflammatory activity.
Lysozyme remains a candidate
The study does not show that lysozyme alone causes the biological findings. Other milk components or combined effects may also be involved.
Raw vs. thermised
The thermised milk retained biological relevance in the model.
An important point of this study is that the selected heat treatment was not accompanied by a complete loss of the findings observed in the mouse model.
Untreated donkey milk
In the stress model, the untreated milk was associated with more favourable findings regarding stress-related intestinal permeability and low-grade inflammatory activity.
Thermised donkey milk
The selected thermised milk also showed corresponding findings in the mouse model. The results were similar, without this implying full equivalence in every single parameter.
Critical assessment
What Study 19 shows – and what it does not
What was examined
What was not proven
Research question for DON DONKEY’S®
What happens to our lysozyme during processing?
The study provides an approach for a product-specific investigation: raw milk, heat-treated milk and freeze-dried milk from the same starting batch should be compared – not only by lysozyme amount but in particular by enzymatic activity.
DON DONKEY’S®
DON DONKEY’S® donkey milk
100 % pure donkey milk
Processing is a decisive factor in the scientific study of donkey milk. Study 19 shows particularly clearly why, for bioactive enzymes, not only their analytical amount but also their actual enzymatic activity should be considered.
Original publication
Effects of thermized donkey milk with lysozyme activity on altered gut barrier in mice exposed to water-avoidance stress
Yvon S., Schwebel L., Belahcen L., Tormo H., Peter M., Ali Haimoud-Lekhal D., Eutamene H., Jard G.
Journal of Dairy Science · 102(9) · 7697–7706 · 2019
PubMed: PMID 31326167
The publication combines milk analysis and preclinical animal research. The results do not constitute clinical proof of efficacy in humans and do not establish a sole causal effect of lysozyme.