Food tests

• Reducing sugars

  Benedict's test:

  • Place 1 cm3 of sample in a test tube.  
  • Add 1cm3 of Benedict’s solution. 
  • Heat at 80 oC in a water bath 
  • If positive, the colour will change from blue to brick red (green -> brick red)
• Non- reducing sugars

  Acid and Benedict's test:

  • Place 1cm3 of sample in a test tube.  
  • Add 5 drops of HCL (acid) 
  • Boil for 3 mins in a water bath 
  • Neutralise with 5 drops of NaOH (alkali) 
  • Add 1cm3 Benedict’s solution 
  • Heat at 80 oC for 5 mins in a waterbath 
  • If Positive, the colour changes from blue to brick red (green -> brick red).
• Non- reducing sugars

  The reducing sugars test must be carried out first. If the result is negative, the non- reducing sugars test can then be carried out.
• Starch

  Iodine:

  • Place 1cm3 of sample in a test tube 
  • Add 3 drops of iodine and shake gently 
  • If positive, the colour will change from brown to black.
• Protein

  Biuret solution (sodium hydroxide & copper sulphate)

  • Place 1cm3 of sample in a test tube.  
  • Add 1cm3 Biuret solution 
  • If positive, it will change from blue to purple.
• Lipids

  Ethanol:

  • Place 1cm3 of sample in a test tube 
  • Add 1cm3 of ethanol. 
  • Shake 
  • Add a few drops of water 
  • Shake 
  • If positive, a white emulsion will form.