New nutritional substitute? Donkey milk touted as potential ingredient for infant and ageing products

This comes after academics performed a data-independent acquisition (DIA) proteomics analysis on milk samples from 84 healthy Dezhou donkeys across seven distinct lactation stages: 1 day (group A), 30 days (group B), 60 days (group C), 90 days (group D), 120 days (group E), 150 days (group F), and 180 days (group G) post-foaling.

These stages generally corresponded to colostrum (1 day), early (30 and 60 days), middle (90 and 120 days), and late (150 and 180 days) lactation phases.

A total of 4870 peptides and 805 proteins in donkey milk revealed a predominant association with various biological systems, including the immune system, global and overview maps, transport and catabolism, signal transduction, the endocrine system, and the digestive system.

Health benefits of donkey milk proteins ​

Specifically, whey protein constituted 58% of the total donkey milk protein, playing a crucial role in preventing milk allergy, as well as exhibiting antibacterial and immune regulatory functions. Both whey protein and casein were found to be linked to oxidation-reduction and carbohydrate metabolic processes.

Furthermore, enzymes such as alpha-mannosidase (FC > 18), alpha-1,2-Mannosidase (FC > 8), Peroxiredoxin 4 (Prdx4, FC > 17), cathepsin B (FC > 10), and lysozyme (FC > 9) were identified in mature donkey milk (30–180 days).

These enzymes played pivotal roles in antibacterial and anti-inflammatory activities, adding another layer of significance to the diverse physiological attributes of donkey milk.

At the same time, researchers also identified 219 down-regulated proteins and 226 up-regulated proteins in donkey milk. The former primarily pertained to immunity and disease resistance metabolic pathways, while the latter predominantly participated in metabolic pathways associated with nutrient metabolism.

Notably, donkey milk from mid and late lactation exhibits a high concentration of selenoprotein F. Selenium (Se), a structural component in numerous proteins, plays a crucial role in physiological processes, including DNA synthesis, toxin scavenging, antioxidant defense, and thyroid hormone metabolism.

Deficiency in selenium can lead to reproductive disorders and muscular diseases. As such, donkey milk from mid and late lactation serves as a promising source for organic selenium supplementation.

The study also revealed that donkey mature milk (30 days–180 days) contains abundant TC, a vitamin B12-specific binding protein that may influence vitamin B12 bioavailability, and SLC36A1, a neutral amino acid transporter involved in nutrient absorption.

The presence of extracellular matrix-related proteins including Beta ig-h3, SPP1, and SRPX in donkey milk proves beneficial for supporting the growth and specialisation of intestinal cells in infants.

Other benefits of donkey milk proteins ​

All along, donkey milk stands out for its unique nutritional value and health benefits, with its dry matter, protein, fat, and lactose content closely resembling that of human milk.

The proteins found in donkey milk have increasingly captivated researchers due to their diverse biological activities, encompassing antioxidant properties, immune stimulation, anti-inflammatory effects, antibacterial attributes, prevention of metabolic diseases, and potential anticancer properties.

According to the researchers, donkey milk has a long history of use in both cosmetic and medical realms. It exhibits the ability to down-regulate the redox-sensitive inflammatory transcription factor NF of the skin fibroblasts-κ B pathway while activates the phosphorylated extracellular regulated protein kinase p-ERK pathway.

Whey protein, enzymes, and collagen present in donkey milk can enhance skin moisture, contribute to anti-inflammatory wound healing, and potentially counteract the effects of ageing in cosmetic products.

Particularly, researchers observe an elevated presence of collagen type XV alpha 1 chain (FC > 9) in mature donkey milk (30 –180 days) compared to colostrum (1 day).

This collagen type demonstrates potential skin benefits, as it has been linked to melanin inhibition, maintenance of stratum corneum moisture, preservation of fibre structure integrity, and skin-related effects such as whitening, moisturising, and wrinkle reduction.

In addition, past research suggest that collagen type XV is implicated in conditions like Dupuytren’s contracture, a hereditary connective tissue disorder in humans, as well as in osteoblast differentiation and mineralisation.

These findings underscore the multifaceted role of collagen type XV in donkey milk, implying its importance not only in skin-related cosmetic effects but also in anti-inflammatory responses and disease resistance.

Even though the content and composition of protein can vary significantly among species, breeds, lactation stages, diets, and seasons and the specific components and mechanisms through which donkey milk exerts its biological activities remain unclear.

Nonetheless, researchers are optimistic that the study has provided valuable insights into the protein profiles of donkey milk.

“Our results provide important insights for understanding the bioactive protein differences in donkey milk in different lactation stages…. [We believe] donkey milk can be used as a nutritional substitute for infants, as well as for cosmetics and medical purposes,”​ Researchers wrote.

Source: Foods

Analysis of the Differentially Expressed Proteins in Donkey Milk in Different Lactation Stages ​

https://www.mdpi.com/2304-8158/12/24/4466​

Authors: Miaomiao Zhou et al.