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Donkey Milk:
A Very Recent Nutritional 'Ph"rmafood"
Introduction
ilk forms an integral part of human diet as it
provides essential nutients and plays a significant
role in both healthy as well in diseased conditions.
Certain individuals suffering from milk allergy caused
by milk from bovine source seek milk from non-bovine
sources. Compared to any non-bovine animal milk, the
donkey milk is closest to human milk and shares lots of
nutritional qualities. It also possesses higher amount of
anti-inflammatory omega-3 fatty acids compared to cow's
milk.The donkey, Eqaus africanusasinus, is a domesticated
member of the Equidae family. The domestication of
the donkey began about 6000 BC in Lrbya. Over the
centuries, donkeys have sptead in Asia, India, South
America and Southern Europe $irillo et aL,2010).
Donkey's milk yield
Researchers had reported that donkey's milk yield
was significandy higher in evening milking as compated
to moming milking (949.3 nJ, and 549.2 mL, respectively).
Furthermore, milk production also affected both by
breed and the breeding season. For example, the donkeys
that foal in the autumn-winter period yielded more
milk than the donkeys reproducing in spring-summer
period.
Biochemical components in donkey milk
The main milk components of donkey milk are
w^ter, fat, protein, carbohydrates, minerals and vitamins
(Table 1). Despite no phylogenetic relationship, donkey
and human milk have similar lactose, total protein and
whey protein contents. Donkey milk also shows a
homogeneous nutritional profile
that is particulady suitable to be
utilized by sensitive populations,
infants and elderly (Guo et a1,2007).
Protein
The total protein content of
donkey milk is quite low (1.5-1.8
g/100 g) as compared to bovine
milk (3.1-3.8 g/100 g), butis closer
to the human milk (0.9-1.7 g/100
g). The protein fraction of donkey
milk is htghly rich in whey proteins, which comprises
about 35-50oh of the nitrogen fracion, while in bovine
milk it comprises onlv 20oh. The thtee major donkey's
milk whey proteins ary. u.-La (1.80 mg/ml, 22.560/0), P-
Lg (3.75 mg/ml, 29.85o/o), and lysozyme (1.00 mg/
mI,27.03oh). In addition to these three, thete ate
immunoglobulins (Igs) (11.5%), blood serum albumin
(BSA) (6.2%) and lactofercin (4.5oh) (Table 2). Donkey
milk also has noticeably higher levels of serine, glutamate,
atginine, and valirie (Table 3). The content of seven out
of the eight essential amino acids (isoleucine, leucine,
lysine, methionine, phenylalanine, threonine, tyrosine, valine)
Composition of donkey\ rnilk
72 ImonN DennmN |ur-v 2018
Table 1: Chemical composition of milk from diffetent species (Guo ef dl, 20A7)
Total solids
0'9-1'7
- ^r, '0-3216.42
Casein 0'64-L03-- ? !6=?20= it:X21
SThey protei 0.49-0.80 .68-0.83
/.u- 1,
Table 2: Protein composition of milk from different species (Uniacke-Lowe ef dl' 2070\
Total casein 0.77
Crsl- casein
3.87
0.1.4
6.2
Serum albumin
ne
Ptoteose
I-*""" 0.
0.03
0.96
0.02
Lactoferrin
NPN (mg/L)
Casein micelle size (nm)
furv 20L8 DennaeN
E!E
ffi?TilK Table 3: Amino acid composition of milk from different animals (Gua et aL,2007)
Aspanic acid 8.9 7.8 8.3
Serine 6.2 4.8 5.1
Glutamic acid 22.8 23.2 17.8
Histidine 4.6 3.4 4.0
Threonine 3.6 4.5 4.6
3.5 3.0 4.0
Proline 8.8 9.6 8.6
Cystine 0.4 0.6 1,.7
3.7 4.5 4.7
Methione 1.8 1.8 1.8
Lysine 7.3 8.1 6.2
Isoleucine 5.5 4.2 5.8
Leucine 8.6 8.7 10.1
Phenylalanine 4.3 4.8 4.4
1.5 1.8
Tryptophan
0.32-0.6 0.19 3.90
Table 4: Fatty acid composition of different milk types (Salimei et dl,2004)
0.28-1,.22 0.15 2.50
C8:0 8.52-1,2.8 0.46 1.50
C10:0 1,8.65-20.42 1,.03 3.20
C1,2:0 10.67-1,5.9 4.4 3.60
c1.4fi 5.77-r0.59 6.27 11.10
C1,4t1, n5 0.22-0.88 0.80 0.41
C15:0 0.32-0.57 0.43 1,.20
C16:0 1,1,.47 -29.1.7 22.00 27.90
C1,7:0 0.22-0.52 0.60 0.58
c17.1 0.27-0.73 0.37 0.36
C18:0 1.12-3.91 8.06 12.20
C18:1 n9 9.7-22.1,5 31,.30 17.20
C18:2 n6 (I-A) 8.1,5-1,5.1,7 10.85 1,.40
6.32-1,6.33 1.03 i.BO
C18:3 n3(ALA)
C20:0
C20:5 0.27 0.1.2 0.09
0.05 0.12 0.20
C22:6 0.30 0.25 0.01
SFA % total fatty acids 46.7-67.7 39.41.-42.24 55.7-72.8
MUFA oh total fatty aqids 1,5.3-35.0 44.30-45.1,1 22.7-30.3
PUFA o/o total fatty acids L5.2-30.5 15.48 2.4-6.3
NE
PUFA n6 oh total fatty acids 11,.57-1,3.09 1,1,.1,7 -1,4.1
ALA = al
74 DannaaN li.nolenic acid: LA = linolei.c acid: NC = trot calcwlated NC
]ur-v 20L8
Table 5: Vitamin content of milk from different species
0.017 0.32-0.50 0.3-0.7
Vitamin A.051 0.98-1.28 3-8
Vitamin E3.5-5.0 0.94 50-100
Vitamin C0.41, 0.37 0.003-0.015
Vitamin 81 0.64 1.8 0.4-06
Vitamin 82 0.74 0.9 1.7
Vitamin 83
Vitamin B12 0.5
r.1 0.004
is also higher than that of bovine milk. All these above-
mentioned factors make donkey's milk, similar to human
milk (Gua et a|,2007; Uniacke-Lowe et a/,201'0).
Fat and fatty acids
Fat content of donkey milk ranges from 0.2\oh to
1.820 and compatable to that of human milk. The lipid
content i," charactertzed by high levels of essential fatty
acids and low saturated fatty acids (SFAs). Donkey milk
also shows similarity to horse milk in having similar fatty
acid profile, although donkey milk shows a higher
concentration of SFAs compated to horse's milk, while
latter has a higher content of monounsaturated fatty acids'
Amazingly, butyric (Cn), captoic (Cu) and lauric (C,r.)
acid content were consistent with horse's milk; however,
lowet contents for caprylic (C, ) and caprtc acid (C,0.)
were observed. Donkey's milk is also rich in poly"rnsaturated
fatty acids €UFA), which also predominate in human
milk (15-20%), with a high percentage of linoleic acid
(essential in that PUFAs, not synthesizedby the organism),
a low <o-6 to trl-3 ratio (Table 4). Hence, all of the above
factors seem to have a positive effect on human health
by providing immune-stimulant properties, cholesterol-
lowering agents, preventing the formation of blood clots
and minimizing the risk of coronary heart disease,
hypetension and thrombosis.
Lactose
The lactose content of donkey milk ranges ftom 6
to 7o/o and is higher than that of cow mtlk (4.1'-4.4o/o).
This high lactose content in donkey milk is responsible
for osteogenic activity, including enhancement in intestinal
absorption of calcium and phosphorus and influences
the mineral accumulation in bone structure, which helps
in the prevention of osteoporosis' In addition to this,
lactose also contributes a good taste to donkey milk
Q-acono et a|,1.992)'
Vitamins
The high content of vitamins present in donkey's
milk make it an excellent nutritional food. Yitamin B1'2
(cobalamin), which is responsible for maintaining healthy
nerve cells and helps in producing DNA and RNA, is
present in much higher concentration than bovine and
human milk (Table 5). The reported total vitamin C
content present in donkey milk represents the
recommended daily intake of vitamin C for children
aged 6-1.2 months.
Mineral and trace elements
The mineral and trace elements composition of
donkey milk is neady similar to human except fot higher
levels of calcium and phosphotus in donkey milk. In
spite of that, donkey milk contains similar concentrations
of essential trace elements such as Zrt, Co and I with
human milk, whereas Fe, Cu, and Se concentrations are
lower.
Microbiological content and chemical
contaminants of donkev milk
Donkey milk possesses low total microbiological
plate count, in the nnge of 2.40-5.87 log cfu/ml. The
reason for the lower mictobial count might be due to
the good health record of donkeys, the excellent natutal
anatomical position of the udder, small size of the udder
and thetefore, Limit exposure of the teats to bacterial
contamination, as well as to the presence of nattxal
antimicrobial components, such as lysozyme'
immunoglobulins, lactofertin, and lactoperoxidase etc.
A recent study also revealed that donkey milk did not
pose any toxicological risk of persistent organic pollutants
and dangerous residues fot consumers' health' Indeed,
Hg and as are within the permitted range, while Cd and
Pb were infrequendy reported. In addition, donkey milk
was reported to possess thE I-'actobacillus rhamnosus, which
contributes to balanced gut environment of consumers
and provides local and systemic immunomodulation'
So, donkey milk is a suitable food to be consumed by
people udth inflammatory bowel diseases such as Crohn's
disease and ulcerative -colitis.
Functional and therapeutic properties of donkey
milk Donkey milk is not only a balanced diet but can
Jurv 20L8 L.roreN DemnaaN 75
*k
also play an important role in preventing diseases and
in promoting well-being. Researchers are focusing on
its nutrient composition and related health benefits. There
is a steady increase in the demand of donkey milk across
Europe especially in France, Italy, Hungary, and, the
Nethedands for its therapeutic potential.
Antimicrobial activity
Donkey milk contains several antimicrobial proteins,
namely lysozyme, lactoferrin, and lactoperoxidase. which
have the abiliry to inhibit the growth ofa broad spectrum
of bacteria. Additionally, they have the ability to reduce
the incidence of gastrointestinal infections in the digestive
tract. Important)y, the presence of lysozyme in donkey
milk, which is absent in other milk-producing species
signifi cantly contributes towards antimicrobial property.
The concentration of lysozyme in donkey milk is about
1,.0 g/L. The high lysozyme contenr of donkey milk is
mainly responsible for the lovz bacterial count and thus,
also makes this milk suitable to prevent or reduce
gastrointestinal infections in infants. Donkey milk has
been used as an alternative to egg lysozyme in cheese
making for the inhibition of spore-forming clostridia
strains causing late blowing in hard Itahan cheeses.
Additionally, lysozyme in donkey milk also inactivates
certain viruses, reduces inflammation and tumor growth.
Lactoferrin is an iron-binding protein and acts as
an antimicrobial agent by hydrolysing glycosidic bonds
of mucous polysaccharides in bactirjal cell walls.
Concentration of lactoferrin is reported to be higher in
donkey milk than that of bovine milk. Bacteriocin_
producing strain of L. paracasei, L. plantarum was also
isolated from donkey milk, This bacieriocin was found
to possess antimicrobial properties against several
pathogenic bacteria such as Salmonella {tplti, pseudomonas
a e rugi n o v, E. co li, U s te ri a m o n o qt toge n e s, E n te ro c o c c u s fae ci u m,
and Lactobacillrc curaatus. Recently, three bacterial strains
belonging to the Enterococcus genus were isolated from
raw donkey milk that produced enterocins (type A, B,
P), which are very active against Listeria mlnnArtugeiles.
Donkey milk was traditionally used as a naturallemedy
to treat pertussis (whooping cough), which is a very
serious disease that can cause pneumonia, seizures, and
ultimately death.
Bioactive peptides in donkey milk
In addition to bioactive miik proteins (casein and
whey proteins), there are many bioactive peptides that
are present in the amino acid sequence of the milk
proteins. Donkey milk on acidification, followed by
hydrolysis by pepsin and in-aitro digestion, yield additional
antimicrobial components other than lysozyme. All these
encrypted amino acid sequences in milk protein contribute
to inhibitory property against the growth of the parhogens.
However, this inhibitory effect was noticeably enhanced
on digestion compared to raw milk samples. Thus, the
antimicrobial activity might result from a synergistic effect
of peptides released by gastrointestinal enzymes together
with intact proteins, such as lysozyme. Bidasolo u.rd .o_
workers (2012) reported that in-aitro simulating
gastrointestinal digestion with pepsin and a mixture oi
pancreatic proteases of donkey milk, produced a B_casein
d:r11.d peptide with potent angiotensin-converting enzqe
(ACE)-inhibitory activity. Several studies also reported
the antiviral activity of various fractions of donkey;s milk
proteins against Echovirus type 5, which primarily affects
the gastrointestinal tract.
Growth factofs and hormones
Donkey milk contains several qrowth factors and
hormones such as human-like leptin,-insulin-like growth
factor 1,, ghrelin, and tri-iodothyronine (I3). These molecules
play a direct role in metabolism, body composition and
in regulating food intake.
fmmunomodulation activity
Donkey milk induced the expression of activation
cell surface molecules such as CD2S, which is used to
track disease progression and CD69, a signal transmitting
receptor in lymphocytes and peripheral blood niononucleai
cells (PBMCs) and also, has the ability to induce the
release of interleukins such as IL-2,IFN_% IL_6, TNF_
a,, and IL-1B from lymphocytes and macrophages. These
cytokines mainly contribute to the immune_enhancing
mechanism of donkey milk. In addition, donkey milf,
induces nitric oxide release from pBMCs. All these
immunological activities expressed by donkey milk may
be useful in the prevention of atherosclerosis, by acting
as a vasodilator and as an effective agent in preventing
pathogens or release of their products.
Hypo-allergic propery
The main allergens responsible for more than g5o/o
of food allergies are proteins present in mi-lk, egg, peanuts,
tree nuts, shellfish, wheat, sesame seed, and soy. Cow
milk protein allergy (CMPA) is.an abnormal immunological
res.ponse to cow milk proteins in certain individuals. Donkey
milk can serve as an alternative to cow milk in thesl
individuals. The low a,llergenicity of donkey,s milk is mainly
due to the low casein content. Donkey milk is also easily
digestible because of its high whey protein content.
Anti-aging property
Donkey milk contains anti-bacterial enzymes and
anti-allergens, which are suitable for persons with sensitive
skin, eczema, acne, and allergies. In addition, it has high
76 lruoreN DarnwaN Jurv 2018
levels of vitamins and minerals, especially, retinol, which
is a huge f^ctor in fighting wrinkles. Retinol aids in
accelerating collagen production and is recommended
for preventing eady signs of aging. Donkey milk has an
appropriate vitamin and mineral composition needed by
skin and body to regenerate and stay healthy. It has 4
times more vitamin C than cow's milk, which can provide
protection against variOus degenerative diseases due to
oxidative stress in human bodY.
Fermented products from donkey milk
Donkey milk is a good base ingredient for functional
food preparation due to its low initial microbiological
load and high lysozyme content. High content of lactose
in donkey milk favouts the growth of probiotic lactobacilli.
Recent studies show that incubation of pasteurized donkey
milk with the probiotics, L. rhamnosus (NT 194, GTI/1',
and GT L/3), L. paracasei, L. breuis, L. saliuarius and L.
plantarun gives good fermented products. This may be
due to the high content of lysozyme in donkey's milk. L.
rhamnosus inhibits the growth of most harmful bacteria in
the intestine and acts as a natwral preservative in yoghurt
and other dairy products in otder to extend the shelf-
life. In all cases, they found that the strains remained
viable even after 30 days of storage, and the Iysozyme
activity was unchanged with resPect to initial values.
Fermented beverage made by L. casei strain developed a
more acceptable and balanced arom^. Similar results were
obtained with other probiotic strains of LAB, namely'
L. acidophilus ATCC 4356 and L. ferrztentum ME-3.
Furthermote, fortification of these products with Na-
caseinate, pectin, and threonine or the addition of flavours
can enhance the rheological and sensory quality.
Application of donkey milk as cosmeceutical
In tecent years, the cosmetic industry is mainly focused
to\Fards products made with natural ingredients due to
various harmfirl side effects of synthetic ingredients. Because
of their nataral origin, milk components correspond in
many fields to the needs of cosmetology. Recent scientific
study on ^ cream containing lyophilized donkey milk
showed different beneficial effects on skin. These results
are related to the effectiveness of donkey milk components
like proteins, minerals, vitamins, essential fatty acids, bioactive
enzqe and coenzyme which provide balanced nourishment
and a proper hydration to the skin. In particular, there is
a higher content of vitamin C in donkey milk (almost 4
times) than cow's milk). Donkey milk contains higher
amount of lactoferrin than cow milk and considerable
amounts of lysozyme, from 1.0 mg/mL to 4 rr'g/mL.
For this reason, donkey milk has the potential to reduce
skin problems such as eczema, acne, psoriasis and herpes
and irritation symptoms. Nowadays, donkey milk is
also used in the manufacture of soaps, lotion and serum
etc. Commercial ptoduction of donkey milk
The sale of donkey's milk has always been a flourishing
practice in Bengaluru. Now it has become even more
so, with villagers from within the state and from the
neighbouring state of Tamil Nadu making the rounds
on the streets of Bengaluru selling donkey's milk for
{ 50/15mL. In these communities, it is given to newborns
as it enhances growth, promotes brain development,
and improves voice and it is also considered to be an
effective remedy for cough, liver problems, loss of appetite
and fatigue.
Conclusion
Donkey milk with various functional properties
carr serve as an alternative to human milk. It can be the
best "pharmafood" for individuals suffering ftom different
food allergies and various skin disorders. It can be a
unique and effective temedy fot Bordetella pertussis
(whooping cough), Iiver diseases, and inflammation-related
gut and skin disorders. However, further research is
required to improve breeding practices so as to enhance
milk production and potential effects on milk quality,
yield, nutritional quality and evaluation of possible
bioactivities. Professional and well-organized donkey
farming is also required to inctease the availability of
milk. References
Readers are advised to contact the authots for
references quoted in the paPer.
Saoita Deoi
Ph.D. vbolar,
Aninal Biochenistry Diuision,
NDKI, Karnal
s aui taj o h n4 @gn ai l. co m
Kamal Gandbi
S cientist
Dairy Chenistry Diuision,
NDRI, Kamal
k a n a lga n d h i n d ri@gm a i l. c o m
Seema Rana
Senior Research Fellow
Dairlt Cbenistry Diaision
NDBI, Karnal
s e e m ara n an dri@gn ai /. co n
Sumit Arora
Principal Scientist
Dairy Chenittry Diuision
NDRI, Karnal
Jurv 20L8
rt/mitdkl 2h.ronN DarnnaaN 77