Testing for Sugars

Testing for Sugars

Benedict’s reagent is used to test for reducing sugars which includes all monosaccharides and the two disaccharides, maltose and lactose. The regent contains copper sulphate and it’s this which reacts with the reducing sugars.

To conduct an experiment you take your sample and add a little amount of Benedict’s solution to it. You then place this into a water bath for up to 10 minutes. During this time you should be able to assess how much glucose is present in the sample.

Colour Amount of sugar present

Brick red/brown

None?Increase in sugar present

A high concentration

Non-reducing sugars like sucrose cannot be reduced by Benedict’s reagent. However, if sucrose is hydrolysed into glucose and fructose by acid hydrolysis then these sugars can be reduced by the reagent.

Testing for starch

Starch can be tested for by using iodine. Simply add a few drops of iodine solution to a sample and observe the colour change:

  • if the iodine remains brown then there’s no starch present
  • if a blue/black colour forms then starch is present