Food tests

• What’s the aim of this experiment?

  To use qualitative reagents to test for a range of carbohydrates, lipids and proteins. To include: Benedict’s test for sugars, Iodine test for starch, the emulsion test for lipids and the Biuret reagent for protein
• What will you do in this experiment?

  • Use qualitative reagents to test for the presence of key biological molecules in a range of foods
  • Safely use appropriate heating devices and techniques including the use of a Bunsen burden and a water bath
  • A qualitative food test indicates if a substance is present or absent in a sample (although it doesn’t tell you how much is present)
  • Observations are essential in this practical; you are looking for colour changes in particular which can indicate if a substance is present or absent:
• What is the food test for starch?

  Iodine
• What is the colour of iodine?

  Orange-brown
• What colour is a positive test for starch?

  blue-black
• What colour is a negative test for starch?

  orange-brown(no change)
• What is the food test for sugar?

  benedicts
• what colour is benedicts?

  light blue
• whats the colour for a positive benedicts test?

  green to brick-red
• what is the food test for lipids?

  ethanol
• what colour is ethanol?

  colourless
• what colour is a positive test for lipids?

  cloudy emulsion
• what is the test for protein?

  biuret
• what colour is biuret?

  blue
• what colour is a positive test for protein?

  lilac-purple
• how do you prepare a sample?

  • Before you can carry out any of the food tests described below, you may need to prepare a food sample first (especially for solid foods to be tested)
  • To do this:
  • Break up the food using a pestle and mortar
  • Transfer to a test tube and add distilled water
  • Mix the food with the water by stirring with a glass rod
  • Filter the mixture using a funnel and filter paper, collecting the solution
  • Proceed with the food tests
• benedicts test for sugar

  benedicts process

  
• iodine test for starch

  iodine

  
• emulsion test for lipids

  lipids

  
• biuret test for protein

  biuret test

  
• What is a main hazard of Biuret solution?

  It contains copper (II) sulfate
• Why should goggles be worn when using Biuret solution?

  It can be dangerous if it gets in the eyes
• What irritant is found in iodine?

  It irritates the eyes
• What should you do if sodium hydroxide gets on your skin?

  Wash hands immediately
• What is the nature of ethanol in the lab?

  It is highly flammable
• How should ethanol be handled near a Bunsen burner?

  Keep it away from the Bunsen burner
• What should you do with the Bunsen burner during the Benedict’s test?

  Turn it off completely
• What is a general hazard associated with the Bunsen burner?

  It is a fire hazard
• What are the main hazards to consider during the practical test?

  • Biuret solution: contains copper (II) sulfate
  • Iodine: irritant to eyes
  • Sodium hydroxide: corrosive
  • Ethanol: highly flammable
  • Bunsen burner: fire hazard
• food test analysis


  remember