Testing for the presence of sugars

• what is meant by the term ‘reducing sugars’?

  they are sugars that can donate an electron
• what solution can detect reducing sugars?

  benedict’s solution
• how do you carry out the test for reducing sugars?

  1. equal volumes of benedict‘s reagent and the solution being tested are heated to at least 70$^.$c
  2. If a reducing sugar (e.g. glucose) is present, the solution will change colour from blue-green-yellow-orange-brickred
  3. this test doesn't tell you the actual concentration of the reducing sugar so its described as a qualitative test
• whats an example of a disaccharide thats a non-reducing sugar?

  sucrose
• whats one way of detecting a non-reducing sugar?

  1. by first breaking it down into its constituent monosaccharides (e.g. by heating with hydrochloric acid)
  2. benedict‘s reagent needs alkaline conditions to work, so alkali is added
  3. benedict’s is then added and heated as before
  4. if the solution now turns red then a non-reducing sugar was initially present
• whats another way of detecting sucrose (non-reducing sugar)?

  1. use sucrase (an enzyme that hydrolyses sucrose into glucose and fructose)
  2. the benedict’s test will then give a positive result
  3. however, enzymes are specific so sucrase will only hydrolyse sucrose (so other non-reducing sugars will give a negative result)
• whats does biosensor mean?

  a device that combines a biomolecule (e.g. an enzyme) with a transducer, to produce an electrical signal which measures the concentration of a chemical
• why are biosensors important in everyday life?


  they are important in monitoring medical conditions such as diabetes, where an accurate measurement of the concentration of blood glucose is required