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

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Presentation on theme: "Isolation of Casein from Milk ■ Kinds of proteins in milk: 1.Casein 2. Lactalbumin 3.Lactoglobulin They are complete proteins."— Presentation transcript:

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

2 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 Most proteins show minimum solubility at their isoelectric point PH of milk is 4.5-4.8 (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 ■ 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.

4 30 ml Milk 30 ml Distilled Water Measure the pH of the milk 40 ºC Add 2 ml of CH3COOH 10% 60 30 15 45 5 10 20 2535 40 50 55 pH=4.5 Add 2 ml of CH3COONa 25 ºC 60 30 15 45 5 10 20 2535 40 50 55

5 10 ml H2O 10 ml 95% alcohol10 ml ether 10 ml ether-alcohol mix. 80 ml D.w. 10 ml 0.1N KOH ph.ph. Shake well Precipitate

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

7 * Calculations 1L (1 N) KOH = Mwt of casein 1 ml (0.1N) KOH = Mwt. Of Casein 10×1000 1ml (0.1N) KOH = 0.105 g casein = 1 ml HCl Volume of Casine = V B - V T (V B -V T ) x 0.105 = ? g casein/30ml milk Y = ? g casine % Y = (V B -V T ) x 0.105 x 100 30 Samar A. Damiati


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