Chemical tests

• The test for reducing sugars is the Benedict’s test.
• Benedict’s test:

  1. Add Benedict’s reagent to sample
  2. Heat mixture in a boiling water bath for 5 minutes
• When a reducing sugar is mixed with Benedict’s reagent and warmed, a brick-red precipitate is formed.
• Benedict’s test for non-reducing sugars (e.g. sucrose):


  Boil (sucrose) with hydrochloric acid first. It will then give a positive result when warmed with Benedict’s solution.
• The test for starch is the iodine test.
• Iodine test for starch:


  Add a few drops of iodine to sample. If the solution changes colour from yellow/brown to purple/black then starch is present in the sample.
• The emulsion test is used to test for fats and oils.
• The Biuret test is used to identify proteins.
• Emulsion test for fats:

  1. Add ethanol to sample
  2. Shake
  3. Pour solution into water
  4. If fats or oils are present then a white emulsion will form on the surface.
• Biuret test for proteins:


  Add Biuret reagent. Solution will turn purple if a protein is present.