Food Tests

• To make a food sample

  • Break it up using a pestle and mortar
  • Transfer to a beaker and add distilled water to dissolve some of the food
  • Filter the solution
• The test for sugar is benedict's solution
• The test for starch is iodine solution
• The test for for protein is biuret solution
• The test for lipids is sudan III stain solution
• If a food sample is positive for sugar the solution will turn green, yellow or red (red higher sugar concentration)
• If a food sample is positive for starch the iodine will turn blue-black
• If a food sample is positive for protein the biuret solution will turn purple
• If a food sample is positive for lipids the sudan III stain solution will stain the lipids bright red
• If a food sample is negative for sugar it will remain blue
• If a food sample is negative for starch it will remain orange-brown
• If a food sample is negative for proteins it will remain blue
• If a food sample is negative for lipids it will stay the same colour
• To test for sugar

  • Place 5 cm³ of food sample in a test tube
  • Place test tube in a water bath
  • Add 10 drops of benedict's solution and leave for 5 minutes
• Test for starch

  • Place 5 cm3 of food sample in a test tube
  • Add 5 drops of iodine solution and mix the contents
• To test for proteins

  • Place 2 cm3 of food sample in a test tube
  • Add 2 cm3 of biuret solution and mix the contents
• To test for lipids

  • Place 5 cm3 of unfiltered food sample in a test tube
  • Use a pipette to add 3 drops of sudan III stain solution and shake the tube
• Iodine is a irritant to the eyes so goggles must be worn
• Sudan III stan solution is flammable so it cannot be near any lit Bunsen burners