Biological Tests

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  • Biological Tests for...
    • Starch
      • Add Potassium Iodide to the solution
      • If starch is present, solution will turn from yellow/brown to blue/black
    • Reducing Sugars
      • Benedict's Reagent
        • Is an alkali solution of Copper II Sulfate.
      • 1. Add equal amounts of liquid food sample and Benedict's Reagent
      • 2. Heat in a gently boiling water bath for 5 minutes.
      • If reducing sugars are present, solution turns brick red.
        • Forms an insoluble precipitate of Copper I oxide
    • Non Reducing Sugars
      • 1. Perform a Benedict's Test
      • 2. If it is negative, hydrolyse the sample by heating with Hydrochloric acid
      • 4. A second Benedict's test is performed and a positive result will be a Brick Red precipitate.
      • 3. Neutralise the sample with Sodium Hydrogen Carbonate
    • Proteins
      • Biuret Test
      • Add dilute Sodium Hydroxide and dilute Copper Sulfate to the sample.
      • If proteins are present, a violet colour will be seen
    • Lipids
      • Add Ethanol to sample, shake, then pour into water
      • If lipids are present then a white emulsion will appear at the surface


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