Required Practical 04: Food Tests

Question 1

Describe how you would prepare a sample of food to be tested. (3)

Answer 1

1. Grind up food samples using pestle and mortar.
2. Mix with water to make a paste.
3. Filter the paste with funnel and filter paper.

Question 2

Describe how you would test for the presence of starch in a sample. (3)

Answer 2

1. Add 2cm³ of food solution into a test tube.
2. Add a few drops of iodine solution to sample.
3. If starch is present, solution turns from orangey-brown to blue-black.

Question 3

Describe how you would test for the presence of a reducing sugar (e.g. glucose) in a sample. (4)

Answer 3

1. Add 2cm³ of food solution into a test tube.
2. Add 10 drops of Benedict’s reagent to sample.
3. Place the test tube into a half-filled hot water bath to boil for around 5 minutes.
4. If a high amount of reducing sugars is present, the solution turns from blue to having a brick red precipitate.

Question 4

Describe how you would test for the presence of protein in a sample. (2)

Answer 4

1. Add 2cm³ of food solution into a test tube.
2. Add Biuret reagent (potassium hydroxide and copper (II) sulphate) and shake the mixture.
3. If protein is present, solution turns from blue to lilac-purple.

Question 5

Describe how you would test for the presence of lipids in a sample. (5)

Answer 5

1. Add 2cm³ of unfiltered food solution into a test tube.
2. Add a few drops of ethanol to the solution.
3. Add a few drops of water to the solution.
4. Gently shake test tube.
5. If lipid is present, a white cloudy emulsion is formed.

Question 6

What safety precautions should be taken during this experiment (Food Tests) ? (2)

Answer 6

• Wear goggles.
• Make sure there is no naked flame near the ethanol when testing for lipids as it is highly flammable.