Milk is the fluid secreted by the mammary gland, particularly free from colostrum. It is an emulsion of lipids in a solution of proteins, a sugar, and inorganic salts. Other constituents include some organic acids or their salts, vitamins, enzymes and antibodies. We will explain fat determination in milk below.
Precipitation of Casein and fat:
Procedure:
Take 20 ml of milk in a beaker.
Add 1% acetic acid drop by drop.
Stir briskly till a white precipitate is formed.
The precipitate consists of casein and fats.
Filter through the filter paper.
Re-filter if the filtrate is cloudy.
The filtrate contains carbohydrate, lactalbumin, lactoglobulin and inorganic constituents.
Test for Fat in Milk:
Procedure:
Take some of the precipitate on a filter paper.
Press well to squeeze out the excess of water.
Keep the filter paper in open air.
Observation:
A greasy spot will obtained, after all the water has completely evaporated, indicating presence of fat.
Precautions:
wash the apparatus before and after the experiment.
Make sure the filter paper is clean before using it.
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