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Chapter: Biochemistry: Practicals

Preparation of Casein From Milk

Aim : To prepare casein from milk.




To prepare casein from milk.




Casein is the main protein found in milk and is present at a concentration of about 30-40 gms/lit. It is a phosphrous containing protein. Casein can be precipated from milk at its isoelectric pH of 4.8. Casein is insoluble in ethanol and ether and this property is used to remove unwanted fat materials from the preparation.


Materials required


1.           Milk -100 ml


2.           Sodium acetate buffer - 0.2 M, pH 4.8


3.           Ethanol        



4.           Ether


5.      Muslin cloth




100 ml of milk is taken in a 500 ml beaker and warmed at 40° C. 100 ml of acetate buffer is warmed separately. Acetate buffer is added slowly to the milk by constant stirring. The pH of the mixture should be adjusted to 4.8 with the buffer and the pH is checked with pH paper. The suspension is cooled to room temperature and left to stand for 10-15 minutes.


The suspension is filtered through a clean muslin cloth and the precipitate is washed with water. The precipitate collected in another beaker is mixed with 30 ml of ethanol. The solution is filtered to obtained a fat free casein. The procedure is repeated again with ethanol and then with ether. The precipitate is collected in a watch glass and allowed to dry. The casein is powdered and spread on a filter paper to remove the ether completely. The casein powder is weighed and the percentage yeiId is calculated.




The amount of miIk taken = 100 ml.


The amount of casein weighted = X gms


The amount of casein present in 100 ml of milk= X gms


The percentage yeild = 100 x X/100 = Y gms




The amount of casein present in 100 ml of milk = Y gms


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