Test for glucose (a reducing sugar)

• Add Benedict's solution into sample solution in test tube

• Heat at 60 - 70 °c in water bath for 5 minutes

• Take test tube out of water bath and observe the colour

• A positive test will show a colour change from blue to orange or brick red

The Benedict's test for glucose

Test for starch using iodine

We can use iodine to test for the presence or absence of starch in a food sample.

The iodine test for starch

• Add drops of iodine solution to the food sample

• A positive test will show a colour change from orange-brown to blue-black

Testing a potato to prove the presence of starch

Test for protein

• Add drops of Biuret solution to the food sample

• A positive test will show a colour change from blue to violet / purple

  
  

Test for lipids

• Food sample is mixed with 2cm3 of ethanol and shaken

• The ethanol is added to an equal volume of cold water

• A positive test will show a cloudy emulsion forming

  
  
  
  

Test for vitamin C

• Add 1cm3 of DCPIP solution to a test tube

• Add a small amount of food sample (as a solution)

• A positive test will show the blue colour of the dye disappearing