BLBS102-c26 BLBS102-Simpson March 21, 2012 13:51 Trim: 276mm X 219mm Printer Name: Yet to Come
26 Equid Milk: Chemistry, Biochemistry and Processing 513Table 26.10.(Continued)Fatty Acid Common Name Equine Asinine Zebra Bovine HumanC18:2tt 0.46
C18:2ct 0.69
C18:3 γ-linolenic 0.15 0.61 1.00 0.25
C20:2 0.35 0.37 0.07 0.27
C20:3 dihomo-γ-linolenic 0.10 0.10 0.32
C20:4 Arachidonic 0.11 0.14 0.46
C22:2 0.04 0.11
C22:4 0.03 0.09
C22:5 0.04 0.09n-3 SeriesC18:3 α-linolenic 8.00 6.32 5.31 1.80 1.03
C18:4 0.22
C20:3 0.12
C20:4 0.07 0.09
C20:5 Eicosapentaenoic 0.27 0.02 0.09 0.12
C22:5 0.07 0.10 0.19
C22:6 Docosahexaenoic 0.30 0.04 0.01 0.25
Total PUFA 18.00 16.02 22.77 5.82 15.27
Ratio n-6:n-3 1.26 1.17 3.14 2.06 8.09
Ratio C18:2to C18:3 1.26 1.28 2.72 1.55 9.37Source: Modified from Uniacke and Fox 2011.
c,cis;t,trans;i, iso;a, anteiso, PUFA, polyunsaturated fatty acids.16.7:1. As a species, humans are generally deficient inn-3 fatty
acids and have excessive levels ofn-6 which is associated with
the pathogenesis of cardiovascular, cancerous, inflammatory and
autoimmune diseases (Simopoulos 2002).
Equine milk-fat contains a very low level of conjugated
linoleic acid (CLA; rumenic acid, Tables 26.9 and 26.10) which
is virtually absent from asinine milk but is high in ruminant milk-
fats, being produced in the rumen by abortive biohydrogenation
ofn-6 octadecadienoic acid (LA) (see Whigham et al. 2000,
Bauman and Lock 2006, Collomb et al. 2006). CLA has several
desirable effects in the diet; some of the positive health effects at-
tributed to it include: suppression of carcinogenesis, anti-obesity
agent, modulator of the immune system and control of arthero-
genesis and diabetes. Small amounts of eicosapentaenoic (EPA)
and docosahexaenoic acid (DHA) are present in asinine milk
whereas equine milk has only trace amounts. EPA and DHA are
especially important in infant nutrition but their absence from
equine milk is not considered to be a problem as an infant’s liver
can desaturate linoleic and ALA to form EPA and DHA.Structure of TriglyceridesThe distribution of fatty acids in animal TGs is non-random,
apparently so that the TGs will be liquid at body tempera-
ture. Inter-species comparison of the positional distribution of
fatty acids has been determined, using fatty acid and stereospe-
cific analysis, for 11 species: echidna, koala, Tammar wallaby,
guinea pig, dog, cat, Weddell seal, horse, pig, cow and human(Parodi 1982). Generally, the positional distribution of fatty acids
is similar, except for the echidna, with short chain fatty acids
preferentially esterified atsn-3, saturated fatty acids atsn-1 and
unsaturated fatty acids generally atsn-2. In equine milk fat,
C10:0occurs at thesn-3 position, whereas in bovine milk fat,
more C10:0is found at thesn-2 than at thesn-3 position. In
human and equine milk, C16:0is located predominantly at the
sn-2 position which is regarded as favourable for assimilation
by infants and children, whereas in bovine milk, C16:0is equally
distributed between thesn-1 andsn-2 positions. In the milk fat
of the Weddell seal and horse, C18:1is esterified preferentially
atsn-1 but for all other species studied it occurs mainly atsn-3
(Parodi 1982). No information is available on the stereospecific
distribution of fatty acids in the TGs of asinine milk.Equid Milk Fat Globules and MFGMThe fat in milk is emulsified as globules which are surrounded
and stabilised by a very complex emulsifying layer, consisting
of phospholipids and proteins, called the MFGM. Many of the
indigenous enzymes in milk are concentrated in the MFGM.
The glycoproteins in the MFGM of human, rhesus monkey,
chimpanzee, dog, sheep, goat, cow, grey seal, camel, horse and
alpaca have been studied; large intra- and inter-species differ-
ences have been found (see Keenan and Mather 2006). Very
highly glycosylated proteins occur in the MFGM of primates,
horse, donkey, camel and dog. Long (0.5–1μm) filamentous
structures, comprising of mucins (highly glycosylated proteins),