food tests

• What is the aim of the Food Tests practical?

  To test for carbohydrates, lipids, and proteins
• What reagent is used to test for reducing sugars?

  Benedict's reagent
• What indicates a positive result for the Benedict's test?

  A color change from blue to green, yellow, or brick-red
• What reagent is used to test for starch?

  Iodine solution
• What indicates a positive result for the iodine test?

  A color change from orange-brown to blue-black
• What test is used to identify lipids?

  The emulsion test
• Describe the steps and positive result of the emulsion test for lipids.

  • Add ethanol to the food sample and shake.
  • Pour the ethanol layer into distilled water.
  • Positive Result: A cloudy white emulsion forms if lipids are present.
• What reagent is used to test for proteins?

  Biuret reagent
• What are the two main components of Biuret reagent?

  Copper (II) sulfate and sodium hydroxide
• What indicates a positive result for the Biuret test?

  A color change from blue to purple or violet
• What type of test are these food tests?

  Qualitative, indicating presence or absence
• Describe the general steps for preparing a solid food sample for testing.

  1. Break up the food using a pestle and mortar.
  2. Transfer to a test tube and add distilled water.
  3. Mix with a glass rod.
  4. Filter the mixture to obtain a liquid sample.
• What is a key hazard associated with Biuret solution?

  It contains copper (II) sulfate, dangerous to eyes
• What safety precaution should be taken when using Biuret solution?

  Always wear goggles
• What is a key hazard associated with iodine solution?

  Iodine is an irritant to the eyes
• What safety precaution should be taken when using iodine solution?

  Always wear goggles
• What is a key hazard associated with sodium hydroxide?

  Sodium hydroxide is corrosive
• What safety precaution should be taken when using sodium hydroxide?

  Wash hands immediately if on skin
• What is a key hazard associated with ethanol?

  Ethanol is highly flammable
• What safety precaution should be taken when using ethanol?

  Keep it away from the Bunsen burner
• What general safety precaution should be followed when using a Bunsen burner?

  Exercise caution to avoid burns
• If a food sample gives a brick-red precipitate with Benedict's reagent, what is likely present?

  Reducing sugars
• If a food sample turns blue-black with iodine solution, what is likely present?

  Starch
• If adding the ethanol layer to water results in a cloudy white emulsion, what is likely present?

  Lipids (fats or oils)
• If Biuret reagent turns purple when added to a food sample, what is likely present?

  Protein