Food Tests (WJEC GCSE Biology)

Testing for the Presence of Starch, Glucose & Protein

Preparing a sample

• Before you can carry out any of the food tests described below, you may need to prepare a food sample first (especially for solid foods to be tested)

• To do this:

  • Break up the food using a pestle and mortar

  • Transfer to a test tube and add distilled water

  • Mix the food with the water by stirring with a glass rod

  • Filter the mixture using a funnel and filter paper, collecting the solution

  • Proceed with the food tests

Test for starch using iodine solution

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

• Add drops of iodine solution to the food sample

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

The iodine solution test for the starch diagram

In the presence of starch, the iodine solution will turn from brown to blue/black

Test for glucose

• We can use Benedict's reagent to test for the presence or absence of simple reducing sugars, such as glucose, in a food sample

• Add Benedict's reagent to the sample solution in a test tube

• Heat in a boiling water bath for 5 minutes

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

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

Benedict's test for glucose diagram

The steps to carry out Benedict's test for glucose

Test for protein

• We can use biuret solution to test for the presence or absence of protein in a food sample

• Add drops of Biuret solution to the food sample

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

The biuret test for protein diagram

The steps to carry out the biuret test for protein

Food test results table