Biochemical Tests

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  • Biochemical Tests
    • Reducing Sugars
      • Add Benedict's Reagent in excess to a sample
      • Heat the sample but do not let it boil
      • If the test is positive, a precipitate will form
        • This will change from blue through to brick red depending on the amount of reducing sugar
    • Non-Reducing Sugars
      • Boil test solution with hydrochloric acid and the neutralise with sodium hydrogen carbonate
      • Check if reducing by completing reducing sugar test. If no result, try non-reducing sugar test
      • Carry out reducing sugar test
    • Starch
      • Add iodine dissolved in potassium iodide solution
      • If test is positive, solution changes colour from orange to blue-black
    • Lipids
      • Shake substance with ethanol for about a minute, then pour into water
      • If lipid is present, solution turns milky. If not, solution stays clear
    • Quantitative Benedict's Test
      • Make up several different glucose solutions of different, known conc. and same volume
      • Carry out Benedict's Test using same volume of reagent and remove precipitate by centrifuge
      • Calibrate colorimeter using distilled water solution to 0, then measure absorbency of Benedict's solution left over
      • Draw calibration curve showing absorbance against glucose conc. and use this to find unkown


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