Question

Write a test for detecting, presence of fat.

Answer 1

Hint: Emulsion test is one of the tests that is used to detect the presence of fat in a given food sample.
Emulsion is a mixture of two immiscible liquids. It is based on the solubility of liquids. Fats are insoluble in polar solvents like water and soluble in non-polar solvents like alcohols.

Complete answer:
Aim: To detect the presence of fat in a given food sample.
Materials required: Test tubes, test tube stand, sample, ethanol and water.
Procedure:
Take the given food sample in a test tube.
The food sample should be crushed firmly to be filtered or diluted.
Add a few drops of ethanol to the sample that has been obtained after filtration or dilution.
Keep the test tube undisturbed in a stand for 2-3 minutes.
Ethanol will be mixed thoroughly with the sample to give a clear, transparent liquid.
This mixture of ethanol and sample should be added to a test tube containing water.
Observe the changes.
Inference: Appearance of white, milk-like emulsion shows the presence of fat in a given food sample.

Additional information:
Fats are greasy in nature which makes them easily detectable in a food item just by touching. Presence of fat in a food sample can be easily detected by keeping it in a filter paper. If the filter paper is translucent when observed under light, it shows the presence of fat in a given food sample.

Note:
Fats are soluble in alcohol but insoluble in water. Hence, when the sample was added to a test tube containing water, the fat present in the sample did not mix with water and the dispersed particles floated on the surface as white emulsion. This is one of the main characteristic features of fats.