Food Tests

• Benedicts solution used to test for sugars
• Iodine solution to test for starch
• Biruet test used for proteins
• Sudan III test to test for lipids
• Positive benedicts test is a colour change from blue to green, yellow or brick red
• Positive solution for iodine is a colour change from browny-orange to black or blue-black
• Positive biuret test is a colour change from blue to purple
• A positive Sudan III test is a seperate red layer at the top of liquid
• Method for Benedicts test:

  • Prepare a food sample and transfer 5cm^3 to a test tube
  • Prepare a water bath and set it to 75 degrees
  • Add some benedicts solution using a pipette
  • Place the test tube into the water bath for 5 minutes, pointing away from you
  • Record the colour change: from blue to green, yellow or red (positive) no colour change = negative
• Method for Iodine Solution:

  • Make a food sample and transfer 5cm^3 into a test tube
  • Add a few drops to the sample and gentley shake, if starch is present, it will change from browny orange to black
• Method for Biuret Test:

  • Prepare a sample of 2cm^3 of your food sample
  • Add 2cm^3 of Biuret solution and gently shake it
  • If protein is present, the solution will change from blue to purple
• Method for Sudan III:

  • Prepare a sample of food, transfer about 5cm^3 of it into a test tube.
  • Use a pipette to add 3 drops of Sudan III solution and gently shake the tube
  • Sudan III stains lipids and the mixture will seperate out into two layers.
  • If lipids are present, the top layer will be bright red