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Lesson: Chapter 1 — The Chemical Basis of Life

1.3. Lipids 4 of 4

Testing for lipids

TEST The Sudan III test for lipids

Whether a food contains lipids can be confirmed with the Sudan III test.

Method

  1. Put a little sesame oil or coconut oil into a test tube.
  2. Add Sudan III reagent and shake well.

Observation

The oil layer → Red

The oil layer turns red. That confirms the food contains lipids.

Why does this work?

Sudan III is a red dye that dissolves only in lipids. It does not dissolve in water. So the dye collects in the oil layer and nowhere else, colouring it red.

Solubility of lipids

The property "lipids do not dissolve in polar solvents but do dissolve in organic ones" is the entire basis of this test. Without that property, the test would not work.