36 Chapter 2
lipids mostly associate with the fat globule
membrane. They also contain traces of fatty
acids; vitamins A, D, E, and K; and enzymes.
More than 400 different fatty acids have been
identifi ed in milk. The predominant fatty
acids in bovine milk are myristic acid (C 14:0 ),
palmitic acid (C 16:0 ), stearic acid (C 18:0 ), and
oleic acid (C 18:1 ) (Otter, 2003 ).
The fat globule membrane is comprised
mainly of phospholipids and proteins, as well
as lipids, lipoproteins, cerebrosides, nucleic
acids, enzymes, trace elements (minerals),
and some bound water molecules that stabi-
lise and prevent the fat globules from coales-
cence during milk processing and handling.
The fat globule membrane prevents attack
from lipases, which would otherwise break
down the lipids (lipolysis) into short fatty
acids, therefore increasing the amount of
diglycerides, monoglycerides, and free fatty
acids in milk. The free fatty acids are fairly
water - soluble and are situated in milk plasma
and fat. Short free fatty acids situated in the
milk plasma are ionized and more water -
soluble than long free fatty acids ( > C 14 )
found in fat and at the oil - water interface.
Several types of minerals are associated
with the fat globule membrane including
copper and iron in relatively large amounts,
5% to 25% and 30% to 60%, respectively.
Other minerals include cobalt, calcium,
sodium, potassium, magnesium, manganese,
molybdenum, and zinc.typical chemical compositions of milk from
different mammalian species.
Water
Water is the principal constituent in milk,
totaling 79% to 90%, depending on the
species. It encompasses all other constituents
of milk (total solids) that are either dissolved
or suspended in it. In addition, small amounts
of water are hydrated or bound chemically to
lactose, salt, or protein.
Regulations prohibit the addition of water
to raw milk. The water activity in milk is
relatively high, 0.993. The removal of water
from milk results in an increased shelf life,
and this property has been exploited through
the production of powdered milk, from which
the water is removed.
Milk Fat
Milk fat is mostly contained in fat globules
that are protected by a membrane. The con-
centration and composition of milk lipids
depend on several factors including breed,
species, feed, individuality, lactation stage,
milking interval and stage, and presence of
mastitic infection.
The fat globules range from 1 to 20 μ m in
diameter. They are made up of approximately
98% triglycerides, 0.2% to 1% phospholip-
ids, and 0.2% to 0.4% sterols. The phospho-
Table 2.1. Typical chemical compositions of milk from various
mammalian species (g/100 g).
Species Water Fat Protein Lactose Ash
Donkey 90.0 1.3 1.7 6.5 0.5
Buffalo 84.2 6.6 3.2 5.2 0.8
Camel 86.5 3.1 4.0 5.6 0.6
Cow 86.6 4.6 3.4 4.9 0.5
Sheep 79.4 8.6 6.7 4.3 1.0
Goat 86.5 4.5 3.5 4.7 0.8
Human 87.7 3.6 1.8 6.8 0.1
Horse 89.1 1.6 2.7 6.1 0.5
Yak 82.7 6.5 5.8 4.6 0.8
Adapted from Kailasapathy (2008) and Francis (2000)