Food tests (PRACTICAL )

• How do we use chemical tests for carbohydrates,proteins,and lipids ?

  • take your food sample and grind this with distilled water using a motar and pestle (make a paste)
  • Transfer the paste to a beaker and add distilled water.Stir so the chemicals in the food dissolve in the water
  • Filter the solution and remove the suspended particles
• How do you test for starch ?

  • place 2cm^3 of food solution to a test tube
  • add a few drops of iodine solution (its orange )
  • if the solutions blue-black it means starch is present
  • if it stays orange it means there is no starch
• How do you test for sugar ?

  • place 2cm^3 of food solution into a test tube
  • add 10 drops of benedicts solution solution (its blue )
  • place the test tube into a a beaker and fill it half way with hot water from a kettle (leave it for 5 minutes )
  • if sugars present the benedicts solution will change colour
• What does the colour of benedicts solution tell us ?

  gives us an approximate idea of how much sugar there is
• What does a green colour of benedicts solution tell us ?

  there is small amount of sugar
• What does a yellow colour of benedicts solution tell us ?

  there is more sugar present
• What does a brick-reddish colour of benedicts solution tell us ?

  there is alot of sugar present
• The Benedicts test only works for certain sugars e.g glucose
• How to test for protein ?

  • place 2cm^3 of food solution
  • add 2cm^3 of biuret solution (its blue )
  • if the solution turns purple/lilac colour protein is present
• How to test for lipids ?

  • place 2cm^3 of food solution (which is not filtered)
  • add a few drops of distilled water and ethenol
  • gently shake the solution
  • if lipids are present then white cloudy emulsion will form
• Why do you not filter the food solution for lipid ?

  lipid molecules will stick to the filter paper