SB1f- Testing foods

• What is the test for sugars?

  Benedict's test
• What is the test for starch?

  Iodine test
• What is the test for proteins?

  Biuret test
• What is the test for lipids?

  Emulsion test
• What colour does the sample turn if sugars are present?

  Brick red
• What colour does the sample turn if starch is present?

  Blue-Black
• What colour does the sample turn if protein is present?

  Lilac
• What colour does the sample turn if lipids are present?

  Milky white emulsion
• How do you prepare the food sample?

  • Get food and break it up with a mortar and pestle
  • Put crushed food and put it in a beaker with some distilled water
  • Stir it with a glass rod until some of it dissolves
  • Filter out the solution
  • The solution we end up with is our sample
• Benedict's test for reducing sugars


  • Transfer 5cm³ of the sample to a test tube
  • Prepare a water bath to 75 celcius
  • Add about 10 drops of Benedicts solution to the test tube
  • Place it in the water bath for 5 minutes with a test tube holder
  • If there is no reducing sugars it will stay blue, but if there is reducing sugars it will turn brick red.
• Iodine test

  • Take 5cm³ of food sample and add a few drops of iodine solution
  • This turns the solution brown
  • Shake the sample
  • If it contains starch, the solution will turn blue-black
• Biuret test

  • Add 2cm³ of the sample in a test tube
  • Add 2cm³ of Biuret solution (Potassium hydroxide, then copper sulphate), turning it blue
  • Shake the solution
  • If protein is present, the solution will turn lilac
• Emulsion test

  -Take food sample and add 2cm³ of ethanol and shake

  -Then add 2cm³ of distilled water

  -If it turns milky white, lipids are present