Food Tests

• What is the aim of the food tests?

  Conduct qualitative chemical tests for food
• What are the four substances tested in food tests?

  • Starch
  • Reducing sugars
  • Proteins
  • Lipids
• What equipment is needed for the iodine test for starch?

  Food sample, test tube, iodine solution
• What happens to the iodine solution if starch is present?

  It turns from brown to blue-black
• What equipment is needed for the Benedict's test for reducing sugars?

  Food sample, test tube, Benedict's solution
• What indicates the presence of reducing sugars in the Benedict's test?

  A brick red precipitate is formed
• What equipment is needed to test for proteins?

  Test tube, measuring cylinder, Biuret solution
• What color change indicates the presence of protein in the Biuret test?

  The solution turns from blue to purple
• What equipment is needed for the lipid test?

  Food sample, test tube, ethanol, distilled water
• What indicates the presence of lipids in the emulsion test?

  A white emulsion is formed on the surface
• What are the steps in the emulsion test for lipids?

  1. Add ethanol to the food sample.
  2. Pour into distilled water.
  3. Observe for a white emulsion.
• What is a potential source of error in the Benedict's test?

  Subtle color change if concentration is low
• What safety precautions should be taken during the Benedict's test?

  Wear safety goggles and tie hair back
• Why should Biuret solution be handled with care?

  It contains poisonous copper sulfate
• What is the first step in preparing a food sample for testing?

  Grind up food samples using pestle and mortar
• Why should ethanol be kept away from flames?

  Because ethanol is highly flammable
• Why do you mix the ground food sample with water?

  To create a solution for testing
• What is the purpose of filtering the food sample?

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

  Add iodine solution to the sample
• What color change indicates the presence of starch?

  Solution turns from brown to blue-black
• What reagent is used to test for reducing sugars?

  Benedict’s reagent
• What is the procedure to test for reducing sugars?

  Add Benedict’s reagent and boil in water bath
• What indicates the presence of reducing sugars in the test?

  A brick red precipitate forms
• What reagent is used to test for proteins?

  Biuret reagent
• What is the procedure for testing protein presence?

  Add Biuret reagent and shake the mixture
• What color change indicates the presence of protein?

  Solution turns from blue to purple
• How do you test for lipids in a food sample?

  Add ethanol to the sample
• What is the next step after adding ethanol to test for lipids?

  Add water to the sample
• What indicates the presence of lipids in the test?

  A white emulsion is formed
• What are the steps to prepare a food sample for testing?

  1. Grind up food samples using pestle and mortar
  2. Mix with water
  3. Filter with funnel and filter paper
• What are the tests for different food components?

  • Starch: Add iodine solution; turns blue-black
  • Reducing sugars: Add Benedict’s reagent; brick red precipitate forms
  • Protein: Add Biuret reagent; turns purple
  • Lipids: Add ethanol and water; white emulsion forms