Food Tests - Biological Molecules Test

• Benedict's Reagent tests if there are reducing sugars in a sample.
• Benedict's Reagent Test:

  • Add Benedict's solution to a food sample and heat it in a water bath
  • If reducing sugars are present a precipitate will form Blue --> Green (low concentration) or Red (high concentration)
• To test for starch in a food sample, iodine is used.
• Iodine Test:

  • Mix food sample with iodine solution
  • If starch is present the solution will turn blue-black Orange --> Blue-Black
• An emulsion test tests if a food sample contains lipids.
• Emulsion Test:

  • Add ethanol and the food sample in a boiling tube
  • Place a bung on the tube and shake it
  • Pour the mixture into water
  • If it goes cloudy, lipids are present Colourless --> Cloudy
• When lipids are present in the emulsion test, they dissolve in the ethanol and float to the surface forming a cloudy emulsion.
• The Biuret test tests for the presence of proteins in a food sample.
• Biuret Test:

  • Mix potassium hydroxide solution and the food sample to make it alkaline
  • Add copper sulfate solution and if protein is present it will turn purple Blue --> Purple