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What is the Biuret Test for Proteins?

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What is the Biuret Test for Proteins?

The Biuret Test  is often used to determine the presence of peptide bonds in protein. As a  student you will most likely will be testing for the presence of protein in foods.The Biuret test for proteins may also be extended to quantitatively measure the concentration of total protein using spectrometric methods.

The Biuret reagent is the sole reagent in the Biuret Test for proteins. The Biuret reagent contains
  • Hydrated Copper sulphate
  • Potassium hydroxide solution
  • Potassium sodium tartrate

  • Are the alternative reagents for the Biuret Test for Proteins?

    As an alternative to the Biuret Reagent, either of the following solutions may be used to yield comparable results.
    • Sodium Hydroxide and  Copper Sulphate Solutions
    • Fehling’s Solutions A and B

    PROCEDURE

    Three procedures are outlined below using different reagents.
    For each of the procedures, a liquid sample must be prepared from solid foods as follows.

    PREPARATION OF LIQUID SAMPLE
    Crush the solid food, add a little de-ionized water and decant the liquid. This liquid should be used for the food test. The quantity of food crushed and water used depends on the number of tests to be conducted.

    What is the procedure for the Biuret Test for proteins using Biuret Reagent?

    Add 2 cm3 of the liquid food sample* to a clean, dry test tube
    • Add 2 cm3 of Biuret Reagent.
    •  Repeat steps  the steps above with de-ionized water to prepare a negative control and with albumin (egg white) to prepare a positive control.
    • Shake well and allow the mixture to stand for 5 minutes
    • Observe any color change.
                

    What is the procedure for the Biuret Test for protein using sodium hydroxide and copper sulphate solutions?

    • Add 1 cm3 of sodium hydroxide solution (40% or bench solution) and 1% copper (II) sulphate  solution dropwise (one drop at a time) to the food  sample
    • Repeat the steps above with de-ionized water to prepare a negative control and with albumin (egg white) to     prepare  a positive control.
    • Shake well and allow the mixture to stand for 5 minutes
    • Observe any color change.

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