Food tests Biology

  1. Take the food sample and grind this with distilled water using a mortar and pestle. We want to make a paste.
  2. Transfer the paste to a beaker and add more distilled water. Stir so the chemicals in the food dissolve in the water.
  3. Filter the solution to remove suspended food particles.

Testing for starch

Place 2cm3 of food solution into a test tube.

Then add a few drops of iodine solution (which is an orange colour) If starch is present the iodine solution will turn blue black, however if there is no starch present the iodine solution will stay orange.

Testing for sugars Place 2cm3 of food solution into a test

Then add 10 drops of Benedict’s solution which is a blue colour. After place the test tube containing our solutions into a beaker and half fill the beaker with hot water from a kettle.

Then leave this for around five minutes. If sugars are present, the Benedict’s solution will change colour. The colour of the Benedict’s Solution gives us an approximate idea of the amount of sugar present but cannot tell us the exact amount. A green colour tells us that there is a small amount of sugar. A yellow colour tells us that there is more sugar present. A brick-red colour tells us that there is a lot of sugar present. The Benedict’s test only works for certain sugars e.g., glucose. Scientists call these reducing sugars.

The benedict’s test will not work for sugars which are non-reducing e.g., Sucrose.

Testing for Protein

You take 2cm3 of food solution and you add 2cm3 of Biuret Solution (which is a blue colour).

If protein is present then the Biuret Solution will change from blue to a purple or lilac colour.

Testing for Lipids/Fats

You grind your food using distilled water using a mortar and nestle.

We transfer 2cm3 of our food solution to a test tube.

Then you add a few drops of distilled water and a few drops of ethanol. You then gently shake the solution. 

If lipids are present then a white, cloudy emulsion forms.                            Remember that ethanol is highly flammable so make sure no naked flames is present.