2.8 - Food Tests

• How do you prepare food samples for food tests?

  Crush and break up the food using pestle and mortar.

  Mix with distilled water until some has dissolved.

  Filter out any solid particles using funnel and filter paper.
• What is the Benedicts test for?

  Reducing Sugars
• Steps to Benedict’s test:

  1. Prepare food samples
  2. Heat water bath to 75°C
  3. Transfer 5cm³ of food sample into test tube
  4. Add around ten drops of Benedict’s solution into food samples
  5. Place test tube in water bath for 5 minutes
  6. If reducing sugars are present the solution will turn brick red
• What is the Iodine test for?

  Starch
• Steps to Iodine Test:

  1. Prepare food samples
  2. Add 5cm³ to test tube
  3. Add a few drops of iodine solution to test tube
  4. Shake test tube
  5. If starch is present, solution will turn blue-black
• What is the Biuret test for?

  Proteins
• Steps to Biuret Test:

  1. Prepare food samples
  2. Add 2cm³ of food sample to a test tube
  3. Add 2cm³ of Biuret solution to test tube
  4. Shake
  5. If proteins are present, solution would go from blue to pink or purple
• What is the Sudan III test for?

  Lipids
• Steps to the Sudan III test:

  1. Prepare food samples - don’t filter out solids
  2. Add 5cm³ of food sample to a test tube
  3. Add 3 drops of the Sudan III stain solution to the test tube
  4. Gently shake
  5. If lipids are present, they will be stained and as they are not soluble will rise to the top of the test tube - a red layer on top of the solution