Food Tests

You are expected to know how test the presence of a few types of biological molecules using reagents, such as Benedict's solution and iodine solution. Do ensure that you know the procedures for these tests at your fingertips.

Iodine Test (for starch)

To a drop of iodine solution, add a drop of the sample.

If starch is present ➡️ yellowish-brown solution turns blue-black

If starch is absent ➡️ solution remains yellowish-brown

Benedict's Test (for reducing sugars)

To 2 ml of Benedict's solution, add an equal volume of the sample. Mix well. Place the mixture in a boiling water bath for 2 minutes. 

If a lot of reducing sugars are present ➡️ blue solution turns into a mixture with brick-red ppt

If reducing sugars are absent ➡️ solution remains blue

If some reducing sugars are present ➡️ (range of colours may be seen, depending on amounts)

Biuret's Test (for proteins)

To 2 ml of sodium hydroxide solution, add an equal volume of the sample. Mix well. Add 3 drops of copper (II) sulphate solution to the mixture, shaking after each drop. 

If proteins are present ➡️ blue solution turns violet

If proteins are absent ➡️ solution remains blue

👁️‍🗨️ Watch the video below to understand the basis of these tests.