4: food tests

• What should you be able to describe by the end of the video?

  How to carry out chemical tests
• Why is it important to wear safety goggles during the tests?

  All chemicals used are potentially hazardous
• What are the key things to learn for the chemical tests?

  • Chemicals used for each food group
  • Positive results for each test
• What is the first step in preparing a food sample for testing?

  Grind the food with distilled water
• What is the purpose of filtering the solution?

  To remove suspended food particles
• What are the two types of carbohydrates mentioned?

  • Starch
  • Sugars (e.g., glucose)
• How do you test for starch in a food sample?

  Add iodine solution to the food solution
• What color does iodine turn if starch is present?

  Blue-black
• What color does iodine remain if no starch is present?

  Orange
• How do you test for sugars like glucose?

  Add Benedict solution and heat the mixture
• What color indicates a small amount of sugar in the Benedict test?

  Green
• What does a brick red color in the Benedict test indicate?

  A lot of sugar is present
• What type of sugars does the Benedict test work for?

  Reducing sugars
• What is the color of Biuret solution?

  Blue
• How do you test for proteins in a food sample?

  Add Biuret solution to the food solution
• What color change indicates the presence of protein?

  From blue to purple or lilac
• What is the procedure for testing lipids?

  1. Grind food with distilled water
  2. Transfer to a test tube
  3. Add distilled water and ethanol
  4. Shake gently
  5. Look for a white cloudy emulsion
• Why do we not filter the solution when testing for lipids?

  Lipid molecules can stick to filter paper
• What safety precaution must be taken when testing for lipids?

  No naked flames should be present
• What can you find in the vision workbook related to chemical tests?

  • Questions on testing for chemicals in foods