Dairy products and milk-based food ingredients - Natural Food Additives, Ingredients and Flavourings - page 415

With the development of agrarian societies, cows proved relatively easy to
domesticate and manage. They reproduce at a rate that ensures a supply of
replacement animals and their conversion of feedstuffs into milk is acceptably
effi cient. Selective breeding has produced modern high yielding animals; the
average milk yield from UK cows in 2009-2010 was 7096 litres (DairyCo 2010).
Cows' milk is the lacteal secretion of one or more healthy animals excluding the
milk produced between 15 days before and fi ve days after parturition. This milk
contains colostrum, which is compositionally different from normal milk, having
a higher fat, protein, vitamin A and sodium chloride content. It is rich in
immunoglobulin antibodies and other immune components that protect the calf
against disease. The composition of milk varies according to species, breed, age
of the lactating animal, nutrition, climate, season and animal health.

17.2.2 The major components of milk
Milk contains over 100 components. Its composition is understood principally in
terms of the fat, protein, lactose (carbohydrate), vitamins, minerals and water it
contains. The major component of milk is water at 87.3%. Fox and McSweeney
(1998) give the typical composition of cows' milk as 12.7% milk solids, 3.7% milkfat,
3.4% protein, 4.8% lactose and 0.7% ash (minerals). Casein is present at 2.6% and
whey proteins at 0.6%. The energy value of cows' milk is around 276 kJ per 100 g.

Milkfat
Milkfat exists in milk as an oil-in-water emulsion of fat globules ranging in size
between 0.1 and 22 μm and is composed of a range of lipid fractions. Kailasapathy
(2008) reports that the lipid in bovine milk contains 95.80% triacylglycerols,
2.25% 1,2-diacylglycerol, 1.11% phospholipid, 0.46% cholesterol, 0.28% free
fatty acids, 0.08% monoacylglycerol and 0.02% cholesteryl ester. Milkfat contains
the fat soluble vitamins, A, D, E and K. The fatty acids in milkfat range from C4:0
to C18:1 (Table 17.2). Around 65% of milkfat is comprised of saturated fatty
acids, some 32% is monounsaturated fatty acid in the form of oleic acid and
around 3% is polyunsaturated fatty acids. The characteristic fl avour of milkfat is
greatly due to the presence of the volatile short chain fatty acid, butyric acid. The
milkfat emulsion is stabilised by the milkfat globule membrane (MFGM), which
is a surface-active membrane enveloping each fat globule. MFGM is a phospholipid
structure that comprises (Danthine et al . 2000) a polar lipids bilayer, proteins,
enzymes, neutral lipids and trace components.

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Milk proteins
The non-fat milk solids (NFMS) - often termed milk-solids-not-fat (MSNF) -
components of milk are the milk proteins, lactose, the water-soluble vitamins and
the minerals. Milk proteins can be divided into two species: casein and the whey
proteins. Casein constitutes about 80% of the protein and is made up of a number
of subspecies (Table 17.3). It is a micellar protein comprised of casein-phosphate
complexes and exists in milk in colloidal suspension. The subspecies α s1 , α s2 and