Dairy Farming Manual
Introduction ( 5 - 8 )The following notes refer to milk from cows.
Milk is an excellent food for
human beings because it contains essential
Milk is an all-round food stuff
and helps give a balanced diet.
(Numbers in brackets refer to illustrations in the Extension materials of the Manual)
What should you know about Milk Composition?
||Why should you drink milk ?
( 5 - 8 )
1. You should know
||What is milk like ? ( 9 - 12 )
2. You should know what good
||What does milk contain ?
( 13 - 46 )
3. You should know milk contains:
||What affects milk composition ? ( 47 - 58 )
4 You should know:
Note: pages 2-15 use cow's milk as an example.
Why should you drink milk ?
||Milk contains substances which:|
||6 - build your body|
||7 - keep you healthy|
||8 Milk does not contain much:
You need to give food which contains these substances
Properties of MilkState and Colour (9-10)
Milk is yellowish -white liquid which
is secreted from mammals to feed
Freezing Point (11)
The freezing point of milk is not dependent on fat and protein content. Salt is the decisive factor together with lactose. These substances are completely dissolved. As the quantity of salt and lactose in the milk is almost constant, the freezing point will be constant too (between -0.53 and --0.55 C). Deviation from this show that the composition of the milk is abnormal and that probably been adulterated.
Specific Gravity (Density) (12)
The specific gravity of milk measured at 15oC or 20oC is normally 1.028 - 1,033 kg/litre. The specific gravity depends on the protein and fat content. The specific gravity of fat is 0.93, solids-non-fat, 1.6 and water 1.0 kg/litre.
If the milk is mixed with air, by
pumping for example, the specific gravity will be lower. The specific
gravity of the milk collected by a tanker is usually between 1.015 and
1.020 kg/litre. If the specific gravity is lower than 1.01 kg/litre,
this may indicate extraneous water (water content higher that normal).
9 Fresh milk is
||10 It has a:
yellowish-white colour and
pleasant, sweetish smell.
||11 If you make milk cold, it
at a slightly lower temperature
||12 Milk is
Constituents of Milk ( 13 )In general, milk consists of water, fat, protein, lactose, minerals, vitamins and enzymes. The composition of milk depends on the kind of mammal, feeding (type and quantity of fodder), cycle of lactation and number of lactations.
Figure 1: Composition of Milk
Milk fat ( 14 - 16)
Milk fat is present in milk in the form of very small globules. The globules are dispersed in the plasma. they vary from 0.1 to 15.0 um. but differ markedly between species and breeds of milch animals. Ranking the milk of the four important species of domestic livestock by average size of globule gives: buffalo milk, cow milk, goat milk and ewe milk. Comparing breeds, milks with high fat content will usually contain larger globules than milks with a low fat content. The globules at the beginning of lactation are comparatively large. Towards the end of the lactation, there is a tendency for the animal to produce small globules.
Percentages of milk fat are:
skim milk ( 95 - 96.5% ).
What does milk contain ?
|13 Whole milk from cows contain approximately:
4% butter fat
|14 Milk contains some things
we can see.
|15 If you leave milk to stand,
yellowish fat or
Milk fat (continued)
is surrounded by a membrane consisting of a thin layer of proteins and
phospholipids and a number of other compounds. The membrane protects
the globlule, preventing it from joining other globules. Without
such a protective layer, the globules would unite and form large masses
of fat. Some of the copper contained in the milk and about three-quarters
of the phosphatase enzyme is concentrated in the membrane.
The membrane also protects the fat from being broken down by the enzymes present in the milk and thereby causing rancid flavour.
that causes this chemical reaction (catalysis) is called Lipase.
|16 Fat is not soluable in water.
If you look closely,
small globules of fat.
| 17 If you look at a fat globule through
you can see:
a membrane on the
|18 The membrane
protects the fat from
enzymes in the milk
which break down fat and cause bad taste.
|19 Gentle treatment of milk is important
to protect fat globules.
Large globules rise faster from the skim milk than small ones.
Rough treatment breaks down the membrane that protects fat.
|20 Milk fats melt at between 18-40o C.|
|21 Milk products contain different
amounts of fat:
Protein is built up of amino acids. There are about 20 different amino acids of which 8 are essential for adults and 9are essential for children. These essential amino acids must be found in your food every day so that your body could build up and maintain skin, hair and muscles. Milk protein is rich in these amino acids and has, therefore, a very high nutritional value and a high coefficient of utelization compared to proteins from vegitable food, for instance soya.
1 glass of fresh milk (200 cc) provides
about 9% of an adult's daily protein requirement and about 8% of child's.
|22 Milk also contains some things
we cannot see.
Proteins23 For 2-3 days after calving the milk (colostrum) contains:
- high amounts of proteins
|24 You cannot use colostrum for dairy products
because it coagulates when heated. So do not deliver milk to the dairy for 4-5 days after calving.
|25 Normal milk contains
3.4 - 4% proteins
Milk proteins consists of 2 major groups.
About 80 % of milk protein is casein which is made up of a number of components together forming complex particles.
Casein is not significantly altered by normal pasteurization procedures. Heating at high temperatures for some time will change the properties of the casein complex and break down certain amino acids. These changes are organoleptically observed as cooked flavour and brown colouration; physically they are observed as changes in the heat stability and rennetability of the milk.
The composition of the casein complex varies within and between species. Thus the procedures to be followed for the manufacture of certain dairy products vary according to the kind of milk being used. The micella in buffalo milk, for example, are much larger than those in cow milk; moreover, they contain more calcium and phosphorus.
There are two different methods of precipitating the casein:
- by souring
the milk either by the direct addition of acid or by bacterial acid production;
Different names are used for the various states in which casein can exist:
- as it
occurs in milk, whether raw or after heat treat-ment (casein complex);
Whey proteins (serum proteins)
If the milk has not been heat treated, the water-soluble whey or serum proteins stay in the milk serum after the casein has been precipitated by acid or by rennet.
Most of the whey proteins react with
casein when the milk is heated to temperatures of 63 C and above.
The higher the temperature and the longer the treatment, the more of these
proteins will associate with the casein micella. At normal HTST pasteurization
only very small quantities are denaturized in this way. Cheese curd
from milk, heated to a high temperature, will not release whey as ordinary
cheese curd does. Milk-serum proteins in general, and lactalbumin
in particular, have very high nutritional values. Their amino-acid
composition is very close to a biological opti-mum. Whey protein
preparates are widely used in the food industry.
|26 There are two main types of protein in milk:
caseins and whey proteins.
When you sour milk or add rennet (enzyme),
the whey is liquid and
casein precipitates (curdles).
|27 Milk products contain different amounts of
cream 2-3 %