Required Practical 4 : Food Tests

• What are the three main types of macromolecules tested in food samples?

  Carbohydrates, proteins, and lipids
• What safety precautions should be taken when performing chemical tests for food?

  • Wear safety goggles
  • Handle all chemicals with care
  • Avoid naked flames near flammable substances
• Why is it important to grind the food sample with distilled water?

  To create a paste that dissolves the chemicals in water
• What is the first step in preparing a food sample for testing?

  Grind the food sample with distilled water
• What is the purpose of filtering the solution after grinding the food sample?

  To remove suspended food particles
• How do you test for the presence of starch in a food sample?

  1. Add 2 cm cubed of food solution to a test tube
  2. Add a few drops of iodine solution
  3. Observe color change:

  • Blue-black indicates starch presence
  • Orange indicates no starch
• What color change indicates the presence of starch when using iodine solution?

  Blue-black
• What is the procedure for testing for reducing sugars using Benedict's solution?

  1. Add 2 cm cubed of food solution to a test tube
  2. Add 10 drops of Benedict's solution
  3. Heat in a water bath for 5 minutes
  4. Observe color change:

  • Green: small amount
  • Yellow: more sugar
  • Brick red: a lot of sugar
• What color indicates a high amount of reducing sugar in the Benedict's test?

  Brick red
• Why does the Benedict's test not work for non-reducing sugars?

  Because non-reducing sugars do not react with Benedict's solution
• How do you test for proteins in a food sample?

  1. Add 2 cm cubed of food solution to a test tube
  2. Add 2 cm cubed of Biuret solution
  3. Observe color change:

  • Blue indicates no protein
  • Purple or lilac indicates protein presence
• What color change indicates the presence of protein when using Biuret solution?

  Purple or lilac
• What is the procedure for testing lipids in a food sample?

  1. Grind food with distilled water
  2. Transfer 2 cm cubed of food solution to a test tube
  3. Add a few drops of distilled water and ethanol
  4. Gently shake the solution
  5. Observe for a white cloudy emulsion indicating lipids
• What indicates the presence of lipids in a food sample?

  A white cloudy emulsion forms
• Why is it important to avoid naked flames when testing for lipids?

  To prevent fire hazards due to flammable ethanol