Molecules
2017
,
22
, 1964
13 of 32
The phospholipids present in bovine ovine and caprine milks are quantitatively minor constituents
of milk lipids, however they possess beneficial techno-functional properties and are involved in various
physiological processes and nutritionally valuable. Other sources of phospholipids in dairy products
include MFGM fragments and lipoprotein particles, which are believed to be remnants of the mammary
secretory cell membranes. PLs like the MFGM originate from the apical plasma membrane of the
mammary gland secretory cell [
2
,
3
,
158
–
162
].
Although phospholipids only account for 0.32–1.0% of the total lipids of milk, they possess
strong biological activity. The general phospholipid content of several milks is depicted in Table
2
.
The PL content of raw bovine milk is reported between 9.4 and 35.5 mg/100g. The phospholipid
composition consists of PE (19.8–42.0%), PC (19.2–37.3%), PS (1.9–10.5%), and PI (0.6–11.8).
The reported sphingolipid composition of raw milk consists of glucosylceramide (GluCer: 2.1–5.0%),
lactosylceramide (LacCer: 2.8–6.7%) and SM (18.0–34.1%) [
3
]. The phospholipid content of small
ruminants, such as ovine and caprine animals differs to that of bovine animals. Zancada, P
é
rez-D
í
ez,
S
á
nchez-Juanes, Alonso, Garc
í
a-Pardo and Hueso [
131
] reports the presence of 27.6 mg/100 g in
caprine milk, and 29.8 mg/100 g in ovine milk. The phospholipid composition of ewes’ milk consists
of PE (26.1–40.0%), PC (26.4–27.2%), PS (4.96–10.7%), PI (4.16–6.40%) and SM (22.6–29.7%), whereas,
in goat milk, it has been reported as PE (19.9–41.4%), PC (27.2–31.9%), PS (3.2–14.0%), PI (4.00–9.37%)
and SM (16.1–29.2%) [
131
]. It is well documented that the composition, structure, and properties of the
fatty acids in milk are affected by several factors such as the breed, season, milking frequency, stage of
lactation, nutritional status, and environmental conditions [
163
–
165
]. It has also been reported that
these factors also affect the phospholipid content of milk [
161
,
166
–
171
]. As aforementioned, milk fat
is characterised by short- and medium-chain fatty acids (C4–C14). These fatty acids are generally
absent in the PL fraction of milk. PE tends to be highly unsaturated followed by PI and PC, whereas
PC tends to be saturated compared to other glycerophospholipids. Sphingosine (d18:1) is the most
prevalent sphingoid base in milk, that contains 18 carbon atoms, two hydroxyl groups, and one double
bond. The fatty-acid pattern of SM is very uncommon with approximately 97% of the fatty acids were
saturated, including C16:0, C18:0, C18:1n9, C22:0, C24:0 and C23:0. The latter accounts for over 17% of
the fatty acid content of SM [
3
,
172
,
173
].
The peculiar fatty acid composition of SM allows the molecule to form in the cellular
membranes and rigid domains with cholesterol, called lipid rafts, which are involved in different
cellular processes [
159
]. The major sphingolipids in dairy products are GluCer, LacCer, and SM.
Gangliosides are also present in dairy product in low concentrations (0.14–1.10 mg/100 mL) [
174
,
175
].
Lysophospholipids and PA are generally not present in dairy samples and occur due to the enzymatic
activity of phospholipases [
3
]. Their origin is still unclear, but it is thought that could be formed
because of hydrolysis occurring during milk processing or poor sample storage [
2
].
In terms of health benefits, milk polar lipids are now known to have several nutritional benefits.
Sphingolipids and their metabolites including ceramide, sphingosine, and sphingosine phosphate
have been found to be highly bioactive, having important effects on cell regulation and are linked to
many inflammatory diseases [
2
,
23
,
176
–
178
]. Sphingolipids exhibit the ability to mediate intestinal
inflammation and may prevent colon-related diseases including cancer [
179
–
183
]. Research has
also indicated that the chemotherapeutic effects of dietary sphingolipids may also extend to other
cancers such as breast and ovarian cancers [
184
,
185
]. Milk polar lipids in a high-fat diet fed to mice,
did not induce white adipose tissue hypertrophy and inflammation but increased colonic goblet
cells. These effects were attributed to the anti-inflammatory effects of the milk polar lipids, and in
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