1. Determination of the Isoelectric Points of Casein
Due to its amphoteric nature, the solubilty of casein depends greatly on the PH of the medium.

2. Determination of the Isoelectric Points of Casein
Certain proteins e.g. gelatin are relatively soluble in water even at their I.E.P.
BUT maximum precipitation can be obtained at the the isoelectric point by addition of some reagents such as, ethanol which dehydrates the molecule and allow neutralization of charge.

3. * Principle
Using acetate buffer of different PH values the approximate position of the isoelectric point of casein can be obtained by determining the PH of minimum solubility.
The PH of any solution can be calculated from Handerson-hasselbalch equation.
PH = Pka + log [Sodium acetate]
[acetic acid]

4. Tube # 1 2 3 4 5 6 7 0.05% casein solution
in 0.1ml CH3COONa
(ml)
Distilled Water (ml)
0.01M acetic acid (ml)
0.1M acetic acid (ml)
1M acetic acid (ml)

5. * Results PH ppt at 30 min ppt at 10 min ppt at 0 min Tube # 1 2 3 4 56 7

6. * Results PK acetic acid = 4.5 PH = PKa + log [CH3COONa] [CH3COOH]
Samar A. Damiati