Question

How do we test for lipids?

Answer 1

Lipid biomolecules:

1. Lipids are biological compounds that are soluble in oil but not in water.
2. They are highly hydrophobic.
3. Lipids stand out from other biomolecules like carbohydrates, proteins, and nucleic acids due to this distinctive physical property. Lipid structures are incredibly diverse.

Tests for lipid:

The tests that are performed to confirm the presence of lipids are-

Sudan III test:

This test uses Sudan black dye to stain triglycerides in frozen sample sections.

1. The sample is added drop by drop and fully dissolved in chloroform or ether.
2. One drop of Sudan III reagent is added.
3. An appearance of red colour confirms the presence of lipid.

Acrolein test:

Lipids on heating with potassium bisulfite give a pungent odour

1. Sodium bi-sulfate (NaHSO₄ ) or potassium bi-sulfate ( KHSO₄) is taken in a clean dry test tube.
2. The sample is mixed thoroughly drop by drop and heat.
3. An irritating smell of acrolein confirms the presence of lipid.

Solubility test:

lipids being highly hydrophobic floats on water

1. Water, benzene, chloroform, and absolute alcohol are taken to four different test tubes.
2. 3 to 4 drops of the sample are added to each test tube and shaken thoroughly.
3. The presence of drops of oil floating only on the surface of water containing test tubes confirms the presence of lipids as lipids are soluble in organic solvents like benzene, and chloroform.

Emulsification test:

This test is used to determine lipids in wet chemistry. The lipids are suspended in ethanol and dissolved in water. The formation of emulsion gives confirmation.

1. The sample is taken in a test tube followed by 2 drops of oleic acid in it.
2. The test tube is then shaken.
3. 2 drops of the mixture are added to another test tube that contains an equal amount(sample) of 10% caustic soda(NaOH).
4. The formation of emulsion confirms the presence of lipids in it.