biochemical food tests

• reducing sugars:

  1. add equal parts Benedicts to sample in a test tube
  2. heat in a water bath for a few minutes
  3. if a reducing sugar is present, coloured precipitate forms
  4. positive result - colour change from blue, orange, green, brick-red
• reducing sugars:

  • galactose
  • glucose
  • fructose
  • maltose
• non-reducing sugars:

  • sucrose
• non-reducing sugars:

  1. add dilute Hcl to sample and heat in water bath
  2. neutralise the solution with sodium hydrogencarbonate

  use indicator to identify when the solution is neutralised

  3. carry out Benedicts as normal
• starch:

  1. add few drops iodine to sample
  2. positive result - blue black colour
• lipids:

  1. add ethanol to sample and shake to mix
  2. add mixture to test tube of water and shake to mix
  3. positive result - milky emulsion
• proteins:

  1. mix potassium hydroxide with food solution to make solution alkaline
  2. add few drops of copper sulfate
  3. positive result - colour change from blue to lilac