Food tests practical

• Iodine test for starch


  1. Put food sample into test tube
  2. Add few drops of iodine solution to food sample
  3. If starch is present, the solution will turn from brown to black-blue
• Benedict's test for sugar


  1. Add equal volume of Benedict's solution to food sample
  2. Place in water bath for few minutes
  3. If sugar is present, a red brick precipitate forms, if absent solution remains blue
• Biuret test for protein

  1. Add few drops of Biuret regent to food sample in test tube
  2. Stir solution to mix and wait few minutes
  3. If protein is present, solution turns from blue to purple
• Test for lipids

  1. Add ethanol to food sample
  2. Pour mixture into test tube of equal volume of distilled water
  3. If lipids are present, white emulsion is formed on surface of mixture
• Sources of error for food tests practical:

  • Colour change for Benedict's and Biuret test may be subtle and difficult to judge
• Safety precautions for food test practical:

  • tie hair back and wear safety goggles
  • handle Buiret solution carefully as it is contains poisonous and corrosive
  • keep ethanol solution from flames
• Sudan III test for lipids 


  1. Add Sudan III solution to food sample
  2. Mix carefully
  3. If lipids are present a layer of red should from on top.
• What is the test for sugar?

  Benedict's solution
• What is the test for protein?

  Biurett solution
• What is the test for lipids/fat?

  Sudan III
• What is the test for starch?

  Iodine