Isolation of Casein from Milk Kinds of proteins

Isolation of Casein from Milk ■ Kinds of proteins in milk: 1. Casein 2. Lactalbumin 3. Lactoglobulin They are complete proteins.

Casein • The main protein in milk • Present at a concentration of about 35 g/l. • It is a phosphoprotein. • Not a single compound, it is a heterogeneous mixture of αS 1 , αS 2 , β, κ. • Casein exists in milk as the calcium salt, calcium Molecular surface model of caseinate. K-Casein.

* Principle ■ The isoelectric point of a protein (I. E. P. ) : is the PH at which the molecule is electrically neutral • Most proteins show minimum solubility at their (net charge is zero). isoelectric point • When a protein is charged e. g. with a –ve charge, the • PH milk is 4. 5 -4. 8 (its isoelectric point). –ve of molecules repel each other and thus remain in the • Casein alsodoinsoluble in ethanol and this property is solutionisand not precipitate. the preparation. • used Whentoaremove proteinunwanted is neutralfatatfrom the I. E. P. they tend to • precipitate Milk is present high PH than point due at to athe absence of the isoelectric repelling forces of casein and, the high molecular weight of protein.

55 60 5 10 50 45 40 35 25 30 30 ml Milk Add Measure Add 22 ml ml of ofºC CH 3 COOH p. H CH 3 COONa of the milk 10% 40 the 15 20 25 ºC p. H=4. 5 30 ml Distilled Water

Precipitate ph. Shake well 10 ml 0. 1 N KOH 80 ml D. w. 10 ml 10 95% ml ether alcohol ml H 2 O ether-alcohol mix.

0. 1 N HCl VB Blank 10 ml 0. 1 N KOH 80 ml D. W. 3 drops ph. VT

* Calculations 1 L (1 N) KOH = Mwt of casein 1 ml (0. 1 N) KOH = Mwt. Of Casein 10× 1000 1 ml (0. 1 N) KOH = 0. 105 g casein = 1 ml HCl Volume of Casine = VB - VT (VB-VT) x 0. 105 = ? g casein/30 ml milk Y = ? g casine % Y = (VB-VT) x 0. 105 x 100 30 Samar A. Damiati