1. Isolation of Casein from Milk
■ Kinds of proteins in milk:
Casein
Lactalbumin
Lactoglobulin
They are complete proteins.

2. Molecular surface model of
Casein
The main protein in milk
Present at a concentration of about 35g/l.
It is a phosphoprotein.
Not a single compound, it is a heterogeneous mixture of αS1 , αS2 , β, κ.
Casein exists in milk as the calcium salt, calcium caseinate.
Molecular surface model of
K-Casein.

3. * Principle ■ The isoelectric point of a protein (I.E.P.) :
is the PH at which the molecule is electrically neutral (net charge is zero).
When a protein is charged e.g. with a –ve charge, the –ve molecules repel each other and thus remain in the solution and do not precipitate.
When a protein is neutral at the I.E.P. they tend to precipitate due to the absence of the repelling forces and, the high molecular weight of protein.
Most proteins show minimum solubility at their isoelectric point
PH of milk is (its isoelectric point).
Casein is also insoluble in ethanol and this property is used to remove unwanted fat from the preparation.
Milk is present at a high PH than the isoelectric point of casein

4. Measure the pH of the milk60 30 15 45 5 10 20 25 35 40 50 55 60 30 15 45 5 10 20 25 35 40 50 55
Add 2 ml of CH3COONa
Add 2 ml of CH3COOH 10%
Measure the pH of the milk
40 ºC
25 ºC
30 ml
Distilled Water
30 ml
Milk
pH=4.5

5. Shake well ph.ph. 10 ml 0.1N KOH 80 ml D.w. 10 ml H2O Precipitate
10 ml 95% alcohol
10 ml ether
10 ml
ether-alcohol mix.
10 ml H2O

6. 0.1N HCl VB VT
Blank
10 ml 0.1N KOH
80 ml D.W.
3drops ph.ph.

7. * Calculations 1L (1 N) KOH = Mwt of casein
1 ml (0.1N) KOH = Mwt. Of Casein
10×1000
1ml (0.1N) KOH = g casein = 1 ml HCl
Volume of Casine = VB - VT
(VB-VT) x = ? g casein/30ml milk
Y = ? g casine %
Y = (VB-VT) x x 100 30
Samar A. Damiati