Food Tests (Cambridge (CIE) IGCSE Biology) : Revision Note

Food tests in biology

Food test for glucose (a reducing sugar)

• Add Benedict's solution into sample solution in test tube

• Heat at 60 - 70 °c in water bath for 5 minutes

• Take test tube out of water bath and observe the colour

• A positive test will show a colour change from blue to orange or brick red 

Use this image

 Food test for starch

• We can use iodine to test for the presence or absence of starch in a food sample.

Use this image

• Add drops of iodine solution to the food sample

• A positive test will show a colour change from orange-brown to blue-black

Use this image

Food test for protein

• Add drops of Biuret solution to the food sample

• A positive test will show a colour change from blue to violet / purple

Use this image

Food test for lipids

• Food sample is mixed with 2cm³ of ethanol and shaken

• The ethanol is added to an equal volume of cold water

• A positive test will show a cloudy emulsion forming

Use this image

Food test for vitamin C

• Add 1cm³ of DCPIP solution to a test tube

• Add a small amount of food sample (as a solution)

• A positive test will show the blue colour of the dye disappearing

Use this image