B1.7 - Food Tests (Practical)

• Which test is used to detect the presence of reducing sugars (i.e. small sugars like glucose)?

  Benedict's test
• Does the Benedict's test require heating the sample in a water bath? 

  Yes
• Benedict's solution itself in blue, but if reducing sugars are present then it will change colour depending on the concentration of reducing sugar.

  Green indicates a low concentration of reducing sugar, orange indicates a medium concentration and brick-red indicates a high concentration.

  
• What does iodine test for?

  Starch
• Iodine solution is used to test for the presence of starch. If starch is present, which colour change takes place?

  Orange to blue-black
• To test for proteins we can use biuret solution.
• Biuret reagent can be used to test for the presence of proteins. If protein is present, what colour change takes place?

  Blue to lilac / purple
• Which test is used to test for the presence of lipids?

  Emulsion test
• Emulsion test for lipids 

  1. Place your food sample in a test tube.
  2. Add 2cm3 of ethanol.
  3. Shake.
  4. Add 2cm3 of distilled water.
  5. If a cloudy emulsion forms then lipid was present.
• What are the different food tests covered in the video?

  Benedict's, iodine, buret, and Sudan 3 tests
• What is the purpose of the Benedict's test?

  To test for reducing sugars
• What does the iodine test detect?

  Presence of starch in food
• What does the buret test check for?

  Presence of proteins in food
• What is the Sudan 3 test used for?

  To test for lipids in food
• What is the emulsion test for lipids?

  A test for lipids using ethanol and water
• What is the procedure to prepare a food sample for testing?

  1. Break food using a mortar and pestle
  2. Add crushed food to distilled water in a beaker
  3. Stir until some dissolves
  4. Filter the solution using filter paper
• What temperature should the water bath be set to for the Benedict's test?

  75 degrees Celsius
• What color indicates the presence of reducing sugars in the Benedict's test?

  Green, yellow, or brick red
• What color change occurs in the iodine test if starch is present?

  Changes from browny orange to blue black
• What happens in the buret test if proteins are present?

  Solution changes from blue to pink or purple
• How do you perform the Sudan 3 test for lipids?

  Add Sudan 3 stain and shake gently
• What indicates the presence of lipids in the Sudan 3 test?

  A bright red layer at the top
• What is the result of the emulsion test if lipids are present?

  Cloudy white color appears
• How much food sample is needed for the buret test?

  2 centimeters cubed
• What is the first step in the food testing process?

  Prepare the food sample
• Why should you point the test tube away from yourself in the water bath?

  For safety reasons to avoid burns
• How do reducing sugars differ from non-reducing sugars?

  Reducing sugars can donate electrons, non-reducing cannot
• What is the significance of filtering the food sample?

  To remove solid bits not needed for tests
• What color does the iodine solution start as?

  Browny orange
• What is the role of potassium hydroxide in the buret test for Edexcel students?

  To prepare the sample for protein testing
• What is the role of copper sulfate in the buret test?

  To react with proteins and change color
• What is the final step in the food testing process?

  Perform the specific food test