Food Tests

• What do you have to do before all tests ( apart from Sudan III)?


  Prepare the food sample
• How do you prepare the food sample?

  Crush with mortar and pestle then add distilled water
• What test is for sugars?

  Benedict's test
• What test is for Starch?

  Iodine test?
• What test is for proteins?

  Biuret test
• What test is for lipids?

  Sudan III test
• How do you test for sugars?

  Add Benedict's solution to food sample then heat in a water bath at 75C
• What is the colour change if sugars are present?


  Blue to Green < Yellow < Orange < Brick Red < Brown
• How do you test for Starch?


  Add few drops of iodine solution to food sample
• What colour change occurs if Starch is present?


  Goes from orangey-brown to blue-black
• How do you test for Proteins?


  Add few drops of Biuret reagent to food sample
• What colour change occurs if proteins are present?


  Blue to Purple
• How do you test for lipids?


  Grind food but do not filter it as a sample.

  Add few drops of distilled water to solution then add few drops of ethanol and gently shake.
• What occurs when lipids are present?


  Goes from clear to forming a white cloudy emulsion.
• Why don't we filter lipids?

  Lipid molecules could stick to filter paper
• What is dangerous about ethanol?


  Highly flammable so no naked flames should be near