Food testing - PRACTICAL

• You can use qualitative reagents to test for a range of carbohydrates , lipids and proteins. These qualitative tests show if a substance is present but not how much for example proteins
• Aim - to investigate different types of food to identify the substances they contain
• Apparatus:

  • eye protection
  • Test tubes and rack
  • hot water bath - beaker with boiling water
  • distilled water
  • Benedict's solution
  • iodine solution
  • Ethanol solution
  • biuret reagent
  • food samples
• To test for sugars:

  1. Mix a small food sample with a small amount ( 2cm² ) of distilled water
  2. Add a few drops of benedict's solution and heat in hot water bath for 5 minutes - record any colour change
• To test for starch:

  1. Mix a small food sample with a small amount ( 2cm² ) of distilled water.
  2. Add a few drops of iodine solution - record any colour change
• To test for lipids :

  1. Mix a small food sample with a small amount ( 2cm² ) of distilled water
  2. Add a few drops of ethanol solution and shake to mix - record when a cloudy upper layer forms
• To test for proteins :

  1. Mix a small food sample with a small amount ( 2cm² ) of distilled water
  2. Add an equal volume of biuret reagent and shake to mix - record any colour change .
• Sugars not present -> Benedict's solution -> turns blue

  Sugars present -> Benedict's solution -> green / orange / red
• Starch not present -> Iodine solution -> orange / brown

  Starch present -> Iodine solution -> blue / black
• Lipids not present -> Ethanol -> red upper layer

  Lipids present -> Ethanol -> cloudy upper layer
• Proteins not present -> Biuret reagent -> blue

  Proteins present -> Biuret reagent -> pink / purple