1. You should know 
about the nutrients in milk.

2.    You should know what good quality milk:
looks like
smells like
tastes like.

3. You should know milk contains:
some things you can see;
some you can not.
 

4 You should know:
environment
breeding
affect milk production. things you cannot see (without microscope)

5    -give energy
 

-iron;
-vitamin C and D.

You need to give food which contains these substances
especially for infants
and young children.

Properties of Milk

Milk is yellowish -white liquid which is secreted from mammals to feed 
the new-born. 

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 15^oC or 20^oC 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).
 

a liquid.

pleasant, sweetish smell.

at a slightly lower temperature

than water.

slightly heavier
than water.

Constituents of Milk  ( 13 )

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: 

cream ( 3.5 - 5% ) 
skim milk ( 95 - 96.5% ).

87%    water
 

 4%    butter fat

 9%    solids-not-fat
 

 Fats
 There are many small fat globules in milk.
-fat globules
-skim milk
 

yellowish fat or 
cream ( 3.5 - 5% )
rises to the top of
bluish-white skim milk.

Each globule 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.
(18-19)

The membrane also protects the fat from being broken down by the enzymes present in the milk and thereby causing rancid flavour.

The enzyme that causes this chemical reaction (catalysis) is called Lipase.
 

If you look closely, 
you can see 
 

small globules of fat.

a membrane on the outside
fat on the inside

enzymes in the milk

which break down fat and cause bad taste.

to protect fat globules.  Large globules rise faster from the skim milk than small ones.
 

Rough treatment breaks down the membrane that protects fat.

-  cream 
-  cheese   10-60%

-  ghee 
-  butter    80-90%

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.
 

we cannot see.
 
 

Proteins

- high amounts of proteins
- antibodies which protect calves from disease.

3.4 - 4% proteins
which help to build up our bodies.

Milk proteins consists of 2 major groups. 

Casein

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; 
     - by coagulation after the addition of certain enzymes. 

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); 
     - as it is precipitated by enzymes (sometimes called the paracaseinate complex); 
     - as it is precipitated by acid (acid casein). 

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. 
 

When you sour milk or add rennet (enzyme),

the whey is liquid and

casein precipitates (curdles).

cheese 20-40%