Milk proteins:

• Proteins are most complex organic substances containing C, H, O, N, S, and P. Milk contains approximately 3% non essential amino acids.
• Apart from this the milk also contains non protein nitrogenous substances such as urea, uric acid and ammonia.

There are about 20 types of amino acids found in milk. Among these only 10 amino acids are essential and the rest are non essential amino acids.

• Essential amino acids are valine, isoleucine, phenylalanine, histidine, methionine, tryptophan, lysine, leucine, threonine and arginine.

• The non essential amino acids present in milk are cystein, alanine, glycine, serine, asparagines, glutamine, praline, aspartic acid, glutamic acid, tyrosine.

Proteins are amphitric in nature, i.e. this shows both acidic and basic properties. It has amino group and carboxyl group which act as base and acid.

The major protein found in milk is casein, lacto-albumin, and lacto-globulin.

a) Casein:

• Casein constitutes about 80% of total milk protein.
• It is always found with calcium that is why it is termed as calcium caesinate.
• It is colourless, odourless and tasteless, and can be precipitated with weak acids, alcohol and rennet.
• Casein is easily separated from milk, either by acid precipitation or by adding rennin.
• Casein is dispersed in milk in the form of micelles. The micelles are stabilized by the Κ-casein.
• When the pH of milk is changed, the acidic or basic groups of the proteins will be neutralised.
• At the pH at which the positive charge on a protein equals exactly the negative charge, the net total charge of the protein is zero.
• This pH is called the isoelectric point of the protein (pH 4.6 for casein).

b) Whey proteins:

• After the fat and casein have been removed from milk, one is left with whey, which contains the soluble milk salts, milk sugar and the remainder of the milk proteins.
• The whey proteins are made up of a number of distinct proteins, the most being α-lactoglobulin
• Denaturation of α- lactoglobulin causes the cooked flavor of heated milk.

c) Lacto-albumin:

• It constitutes about 18% of total milk protein.
• It is coagulated by heating but not with the rennet and acids.

d) Lacto globulin:

• It constitutes about 0.5 to 2% of the total milk protein.
• It is coagulated with high temperature but not with rennet and acids.
• It is chief protein in colostrums and provides immunity to the living bodies.