biochemical tests

• carbohydrates-

  Benedict’s Reagent as the test for Reducing sugars (glucose, fructose). A reducing sugar is able to donate electrons (therefore reduce) Benedict’s reagent – heat the benedict’s with the sample in a boiling water bath and if reducing sugars are present, the reagent will turn from blue to give a brick red precipitate. The range of colours in between, green, yellow, orange, give a limited ability to quantitate the amount of sugar present.
• Non-reducing sugars (like sucrose- will not reduce benedicts) do not give a positive result with Benedict’s reagent. If however, they are hydrolysed by boiling with acid, followed by neutralisation with sodium bicarbonate and subsequently tested with Benedict’s, the reducing sugar should give a positive result.
• carbs:

  Clinistix – these plastic sticks possess a small pad of indicator substance which changes colour in the presence of the specific reducing sugar glucose – positive test is pink to blue with sugars.
• Proteins –

  Biuret reagent can be used to test for soluble proteins. A little potassium hydroxide is added to the protein solution followed by a drop of copper sulphate solution down the side of the test tube. When shaken, the solution will turn from blue to lilac/purple of protein is present.
• Protein:

  Ninhydrin – reagent can be used to identify amino acids on chromatograms only. It turns purple when heated in the presence of protein.

  
  

  must be used in a fume cupboard as its a carcinogen
• Proteins:

  Albustix – these plastic sticks possess a small pad of indicator substance which changes colour in the presence of protein – a positive test for protein is yellow to blue.