Food Tests

There are different tests we can use to identify carbohydrates, proteins and lipids in food.

For all the tests, you must first follow these steps:

1. Use a mortar and pestle to break up your food.

2. Place the crushed food into a beaker with distilled water.

3. Stir the mixture with a glass rod until some of the food dissolves.

4. Use a funnel and filter paper to filter the solution, removing any remaining solid bits of food.

Now you can use the final solution for the food tests.

Benedict’s Test for Reducing Sugars

Benedict’s solution is a deep-blue, alkaline chemical reagent, used to detect reducing sugars. Monosaccharides and some disaccharides are reducing sugars.

1. Using a Bunsen burner, set up a water bath and heat it to a minimum of 80 degrees Celsius.

2. Add some of the test sample to a test tube containing Benedict’s solution.

3. Put the test tube in the water bath for 5 minutes.

4. Record any colour change in your results.

If no reducing sugars are present in your sample, the solution will remain blue. However, if they are present, it can change to a range of colours (green, yellow-orange, or brick red) depending on the concentration.

Iodine Test for Starch

Detecting starch or complex carbohydrates in an organic sample:

1. Place some of your test sample into a test tube

2. Add a few drops of iodine solution

3. Record any colour change in your results

If the colour changes to deep blue/black then your sample contains starch.

Biuret Test for Proteins

The Biuret test shows the presence of peptide bonds, which are the bonds that hold amino acids together in proteins. In the test, NaOH and CuSO4 are used.

1. Add an equal volume of sodium hydroxide (NaOH) to your test sample in a test tube.

2. Add two drops of copper sulphate (CuSO4 ) solution and stir for a few minutes.

3. Record any colour changes in your results.

If your food sample contains proteins then the solution will change from blue to purple.

Emulsion Test for Lipids

Lipids are insoluble in water. However, they can be dissolved in an organic solvent like ethanol.

1. Add some of the test sample to a test tube containing ethanol.

2. Shake it until it’s mixed well.

3. Add an equal volume of distilled water.

4. Record any observations in your results.

A white cloudy emulsion will form if your test sample contains lipids. If there is no cloudy white emulsion, then there are no lipids in your sample.