Biochemical tests

• Reducing sugars (glucose/maltose)


  • Benedict's reagents
  • heat to 80C
  • Initial colour of reagent - blue
  • Positive result: Brick red (yellow/orange)
• Test for Proteins

  • Add a few drops of Biuret solution
  • Initial reagent colour; Blue
  • Positive result=lilac/violet
• Test for lipids

  • Ethanol + shake/mix well
  • Add cold water
  • Initial reagent colour: colourless/ clear
  • Positive result=Forms a cloudy white emulsion
• Test for Starch

  • Add a few drops of iodine suspension
  • Initial reagent colour: brown
  • Positive result = blue/black
• Test for non-reducing sugars (sucrose)


  (Following a negative Benedict's test)

  • Boil w/acid first
  • Cool solution then neutralise
  • Test again with Benedict's reagent (hydrolyses glycosidic bond)
  • Positive result = brick red (OR green/yellow/orange)