Food Tests

• preparing a sample

  • grind up food in pestle and mortar
  • place ground up food in distilled water and stir to dissolve a bit then filter out an solid pieces
  • place the result in a test tube ready to be tested
  • clean pestle and mortar after use ready for next test
• benedict's test for reducing sugars

  • heat a water bath to 75 degrees Celsius
  • place food sample in a test tube and drop in a few drops of the blue benedict's reagent to this and swill the test tube to mix
  • place the test tube into the water bath for 5 minutes
  • after five minutes the colour would have either stayed blue indicate a lack of sugars, turned yellow or green indicating a little of sugars or brick red indicating a lot
• Iodine test for starch

  • place orangey-brown iodine reagant into a food sample in a test tube and swill to mix
  • the solution will turn from orange to blue-black if starch is present if not it will remain unchanged
• biuret test for protein

  • add blue biuret reagent to a test tube containing a food sample and swill to mix them
  • if protein is present the solution will turn purple if not it will remain blue
• Sudan III and Emulsions tests for lipids

  • You do not need to filter the test for this to work but a sample that has been filtered still works
  • add a few drops of Sudan III or ethanol to the sample
  • put a bung in the test tube and shake vigorously to combine
  • if lipids are present a red layer on top of the solution will form from the Sudan III or the sample will go cloudy white from the ethanol