Reducing & Non-Reducing Sugars (Cambridge International A-Level Biology)

Spec point — 2.2.4 · state that glucose, fructose and maltose are reducing sugars and that sucrose is a non-reducing sugar

Reducing & non-reducing sugars

• Sugars can be classified as reducing or non-reducing; this classification is dependent on their ability to donate electrons

• Reducing sugars can donate electrons (the carbonyl group becomes oxidised), the sugars become the reducing agent

  • Thus reducing sugars can be detected using the Benedict’s test as they reduce the soluble copper sulphate to insoluble brick-red copper oxide
  • Examples: glucose, fructose, maltose

• Non-reducing sugars cannot donate electrons, therefore they cannot be oxidised

  • To be detected non-reducing sugars must first be hydrolysed to break the disaccharide into its two monosaccharides before a Benedict’s test can be carried out
  • Example: sucrose

The mnemonic to remember the definitions for oxidation and reduction

Exam Hint Become familiar with the OILRIG mnemonic to remember what happens to a molecule when electrons are lost from it (oxidation) or gained by it (reduction).