Proteins:
Milk
protein is very exclusive in nature and it is the natural source of
amino acids. More than 95 amino acids of total declared amino acids
are available in the milk protein. Milk protein is regarded as high
resource and matchless resource of amino acids. Particularly it
contains many essentials amino acids which are not synthesized in
our body and required for normal metabolism. The concentration of
protein in milk varies from 3.0 to
4.0%. The percentage varies with the breed of the cow and in
proportion to the amount of fat in the milk. There is a close
relationship between the amount of fat and the amount of protein
in milk—the higher the fat, the higher the protein. The
protein falls into two major groups: caseins (80%) and whey
proteins (20%). Casein is always present in the form of
calcium caseinate. It is present in the suspicion / colloidal form
in the milk.
Fat:
Normally, fat (or lipid) makes up from 3.5 to 6.0% of milk,
varying between breeds of cattle and with feeding practices. A
ration too rich in concentrates that do not elicit rumination in the
cow may result in milk with a depressed percentage of fat (2.0 to
2.5%).
Fat is present in milk in small globules suspended in water. Each
globule is surrounded by a layer of phospholipids, which prevents
the globules from clumping together by repelling other fat globules
and attracting water. As long as this structure is intact, the milk
fat remains as an emulsion.
The
majority of milk fat is in the form of triglycerides formed by the
linking of glycerol and fatty acids. The
proportions of fatty acids of different
lengths determine the melting point of fat and thus the consistency
of the butter derived from it. Milk fat contains predominantly
short-chain fatty acids (chains of less than eight carbon atoms)
built from acetic acid units derived from fermentation in the rumen.
This is a unique feature of milk fat compared with other kinds of
animal and plant fats. The long chain fatty acids in milk are
primarily the unsaturated acids,
with the predominant one being oleic (18-carbon chain), and
polyunsaturated linoleic and linolenic acids.
Minerals and Vitamins:
Milk is an excellent source of most minerals and vitamins
required for the growth of the young. Differnet minerals found in
milk are potassium, calcium, chloride, phosphorus, sodium, sulfur,
magensium and small amounts of trace minerals. The digestibility of
calcium and phosphorus are unusually high, in part
because they are found in association
with the casein of the milk. Vitamin A, D, E, K, C and B complex are
also found in milk
Factors Affecting
composition of milk
-
The
milk composition depends on the various factors; it may vary
from:
-
Animal to animal
-
Breed to breed of same specie
-
Season to season: Seasonal
variation is very important. In winter, milk is usually high in
nitrogenous contents and in summer season, it is high is
chloride contents.
-
Milking to milking and lactation to
lactation
-
Availability of feed to the animal
Numerical values of various components of milk for different species
are as follows (These values vary with breed to breed):
Species
|
Water
|
Fat
|
Casein
|
Whey
Protein |
Lactose
|
Ash
|
Cow |
87.3 |
4.4 |
2.8 |
0.6 |
4.6 |
0.7 |
Buffalo |
82.2 |
7.8 |
3.2 |
0.6 |
4.9 |
0.8 |
Goat |
86.7 |
4.5 |
2.6 |
0.6 |
4.4 |
0.8 |
Sheep |
82.0 |
7.6 |
3.9 |
0.7 |
4.8 |
0.9 |
Camel |
86.5 |
4.0 |
2.7 |
0.9 |
5.4 |
0.7 |
|