food tests - core practical

• what is the benedicts test used for?

  reducing sugars
• what is the iodine test used for?

  starch
• what is the biuret test used for?

  proteins
• what is the emulsion (ethanol) test used for?

  lipids
• how should you prepare your food sample?

  • take your piece of food and break it up using a mortar and pestle
  • put the crushed food into a beaker with some distilled water
  • stir with a glass rod until some of it dissolves
  • filter out the solution using a funnel lined with filter paper to remove the solid bits of food that you dont need
  • this solution will be the sample
• how to do the reducing sugars test:

  • prepare your food sample
  • transfer 5cm cubed into the test tube
  • prepare water bath and set in 75 degrees
  • once the water bath is ready add about 10 drops of benedicts solution to the test tube and place it in the water bath in a test tube holder for 5 mins
  • no reducing sugars= solution will remain blue
  • reducing sugars = change to green/ yellow or brick red depending on the concentration
• how to do the starch test:

  • take 5cm cubed of your food sample and add a few drops of iodine solution to it in the test tube
  • this will turn the solution a brownie orange colour
  • gently shake your test tube
  • contain starch = solution will change change to a blue / black
• how to do the protein test:

  • add 2cm cubed of your food sample to a test tube
  • add another 2cm cubed of your biuret solution which will turn it blue
  • gently shake the test tube
  • contain protein= pink / purple
• how to test for lipids?

  • take your food sample add 2cm cubed of ethanol
  • shake it vigorously
  • add 2cm cubed of distilled water
  • contain lipid = changed to a cloudy white colour