Food tests

• Benedict's = the reagent used to test food for the prescence of sugar.
• Buiret's = the reagent used to test for the present of protien.
• emulsion = a mixture of two or more different liquids which do not easily mix.
• Ethanol = reagent used in emulsion test for the presence of fats.
• Iodine = the reagent used to test food for the prescence of starch.
• Reagent = a substance or mixture for use of chemical analysis or other reactions.
• Exam question: Name the chemical you would use to test a sample for the presence of starch [1 mark].


  Iodine solution [1 mark].
• The food tests are about testing what type of food molecule a sample contains.
• To prepare a food sample for testing, you have to follow these steps:

  1. Break up the food sample using a pestle and mortar.
  2. Transfer to a test tube and add some distilled water.
  3. Mix the solution with a glass rod to dissolve the food.
  4. Filter the solution using a funnel lined with filter paper, to get rid of the solid bits of food.
• Test for starch (iodine):

  Add the food sample to a test tube. Add a few drops of the iodine solution and gently shake the tube. If the solution contains starch, the colour will change from a browny-orange to a blue-black.
• Test for Protien (buiret):

  Prepare the food sample and add to a test tube. Add a few drops of buiret solution to the test tube and gently shake. If it is positive, the solution will change from blue to purple. If it is negative, the solution will stay blue.
• Test for Lipids (emulsion):

  Prepare a food sample into a test tube. Use a pipette to add a few drops of ethanol into the food sample. if it is positive, the solution should turn into a cloudy white emulsion.
• Test for Sugars (Benedict's):

  Prepare your food sample in a test tube. Then, set up a water bath at 75'C. Add Benedict's solution into the test tube using a pipette. Place the test tub einto your water bath using a test tube holder and leave it for 5 minutes. If the solution is positive, the solution with change from blue to green, yellow or brick-red, depending on how much sugar is present.