AS level Biology Food Tests

Test for starch

Add iodine (potassium iodide solution) to the sample. If the solution goes from brown-orange to blue black starch is present.

Test for lipids

The emulsion test - add ethanol to the sample and shake the test tube then add water to it. Lipids are present if a white emulsion appears.

Test for reducing sugars

The Benedict's test - add Benedict's reagent to the sample then heat the solution gently. A brick-red precipitate indicates that reducing sugars are present.

Test for non-reducing sugars

The Benedict's test (for non-reducing sugars) - add hydrochloric acid to the sample and heat gently, then neutralise the sample with sodium hydrogencarbonate solution. Add Benedict's reagent to the sample. It's positive if there's a brick-red precipitate.

Test for proteins

Biuret test - add sodium hydroxide solution to the sample. Add copper sulphate solution. If proteins are present the solution will turn purple, if not it will stay blue.