02. Food tests

How can we identify what foods contain?

The test for starch (a carbohydrate)

Apparatus

Method

A Take a small sample of your food. If it is not a powder, go to step C. If it is a powder, add it and an equal volume of water to a test tube.

B Put the stopper in the test tube and shake for 10 seconds.

C Use a pipette to add three drops of iodine solution. If a blue–black colour appears, the food contains starch.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

The test for fat

Apparatus

Method

A Take a sample of your food and rub it into the paper for 20 seconds.

B Carefully remove the food from the paper.

C Hold the paper up to the light. If you can see a greasy mark, the food contains fat.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

Results table

The test for protein (using Biuret solution)

Apparatus

Method

A Using a pestle and mortar, mash a small sample of food with an equal volume of water.

B Pour the mashed food and water into a test tube.

C If you do not have Biuret solution then go to step D. Otherwise add 10 drops of Biuret solution and go to step F.

D Add an equal volume of dilute sodium hydroxide solution.

E Now add 10 drops of copper sulphate solution.

F Wait for a couple of minutes.

G If a purple colour appears, there is protein in the food.

- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -

The test for glucose

Apparatus

Method

A Using a pestle and mortar, mash a small sample of food with an equal volume of water.

B Pour the mashed food into a boiling tube.

C Add 10 drops of Benedict’s solution.

D Place the boiling tube into a water bath. Heat the mixture until it boils. Then stop heating.

E Green, yellow and red colours indicate the presence of glucose.

Can you:

> carry out practical instructions safely

> make careful observations

> test for protein, glucose starch and fat