Biochemical Food Tests

Food tests for:

  • Starch
  • Reducing Sugar
  • Non-reducing Sugar
  • Protein
  • Lipid
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Starch Test

  • Add a solution of Iodine (in potassium iodide solution) to the sample.
  • If starch is present colour will change from yellow-brown to blue-black
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Reducing Sugar Test

  • Add Benedict's solution (alkaline copper sulphate) to the sample.
  • Heat to 80C in a water bath.
  • The solution will change from blue to an organge-red precipitate.
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Non-reducing Sugar Test

  • First if the test for a reducing sugar has came back negative (no colour change)
  • Make sure there are no reducing sugars in the solution by boiling with hydrocholoric acid.
  • Cool the solution and neutralise it by adding sodium hydrogencarbonate.
  • Carry out the reducing sugar test again.
  • If non-redcing sugars present the solution will change from blue to an organge-red precipitate
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Protein Test

  • Add Biuret reagent to sample.
  • If proteins are present, the biuret will react with the peptide bonds found in the protein.
  • The solution will change from blue to lilac.
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Lipid Test

  • Mix the sample with ethanol to dissolve the lipid present.
  • Then pour the liquid (alcohol with dissolved fat) into water contained in another clean test tube.
  • If lipid is present, a cloudy white emulsion will form near the top of the water.
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Comments

wade

great thankyou!!!

chad higgins

spelt precipitate wrong jon tut tut

Abigail

Thanks so much for this! - its so hard to found it written down!

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