Test for Fat determination in milk:

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.