|
Page 2 of 16
Milk composition in general
Bovine
milk contains the nutrients needed for growth and development of the
calf, and is a resource of lipids, proteins, amino acids, vitamins and
minerals. It contains immunoglobulins, hormones, growth factors,
cytokines, nucleotides, peptides, polyamines, enzymes and other
bioactive peptides. The lipids in milk are emulsified in globules
coated with membranes. The proteins are in colloidal dispersions as
micelles. The casein micelles occur as colloidal complexes of protein
and salts, primarily calcium [6].
Lactose and most minerals are in solution. Milk composition has a
dynamic nature, and the composition varies with stage of lactation,
age, breed, nutrition, energy balance and health status of the udder.
Colostrums differ considerably to milk; the most significant difference
is the concentration of milk protein that may be about the double in
colostrum compared to later in lactation [7].
The change in milk composition during the whole lactation period seems
to match the changing need of the growing infant, giving different
amounts of components important for nutrient supply, specific and
non-specific host defence, growth and development. Specific milk
proteins are involved in the early development of immune response,
whereas others take part in the non-immunological defence (e.g.
lactoferrin). Milk contains many different types of fatty acids [8]. All these components make milk a nutrient rich food item.
Components in milk and their health effects
Lipids
Fatty acids
In average, milk contains about 33 g total lipid (fat)/l [9] (Table 1).
Triacylglycerols, which account for about 95 % of the lipid fraction,
are composed of fatty acids of different length (4–24 C-atoms) and
saturation [8].
Each triacylglycerol molecule is built with a fatty acid combination
giving the molecule liquid form at body temperature. Other milk lipids
are diacylglycerol (about 2% of the lipid fraction), cholesterol (less
than 0.5 %), phospholipids (about 1%), and free fatty acids (FFA)
accounting to less than 0.5% of total milk lipids [8].
Increased levels of FFA in milk might result in off-flavours in milk
and dairy products, and the free volatile short-chain fatty acids
contribute to the characteristic flavours of ripened cheese.
Table 1.
Milk composition and percent contribution to the daily dietary
reference intakes of some nutrients in 0.5 l whole milk, and their main
health effects
|
Milk composition and percent contribution to the daily
dietary reference intakes of some nutrients in 0.5 l whole milk, and
their main health effects
|
Milk component
|
Concentration in 1 l whole milka
|
Percent contribution of 0.5 l whole milk to reference intakeb
|
Health effects
|
|
Fat
|
33 g/l
|
|
Energy rich
|
Saturated fatty acids
|
19 g/l
|
|
Increase HDL, small dense LDL, and total cholesterol. Inhibition of bacteria, virus
|
Oleic acid
|
8 g/l
|
|
Prevent CHD, gives stable membranes
|
Lauric acid
|
0,8 g/l
|
|
Antiviral and antibacterial
|
Myrisitc acid
|
3,0 g/l
|
|
Increase LDL and HDL
|
Palmitic acid
|
8 g/l
|
|
Increase LDL and HDL
|
Linoleic acid
|
1,2 g/l
|
|
Omega-6 fatty acid
|
Alpha linolenic a
|
0,75 g/l
|
|
Omega-3 fatty acid
|
Protein
|
32 g/l
|
30–40%
|
Essential amino acids, bioactive proteins, peptides. Enhanced bioavailability
|
Lactose
|
53 g/l
|
|
Lactosylation products
|
Calcium
|
1,1 g/l
|
40–50%
|
Bones, teeth, blood pressure, weight control
|
Magnesium
|
100 mg/l
|
12–16%
|
For elderly, asthma treatment
|
Zinc
|
4 mg/l
|
18–25%
|
Immune function. Gene expression
|
Selenium
|
37 ug/l
|
30%
|
Cancer, allergy, CHD
|
Vitamin E
|
0,6 mg/l
|
2 %
|
Antoixidant
|
Vitamin A
|
280 ug/l
|
15–20%
|
Vision, cell differentiation
|
Folate
|
50 ug/l
|
6 %
|
DNA synthesis, cell division, amino acid metabolism
|
Riboflavin
|
1,83 mg/l
|
60–80%
|
Prevent ariboflavinosis
|
Vitamin B12
|
4,4 ug/l
|
90%
|
Key role in folate metabolism
|
|
a data from USDA Food Composition Data [9].
b Dietary reference intake (DRI) for men and women [4].
|
|
