Biuret Test for Proteins

Biuret Test for Proteins The Biuret Test is often used to determine the presence of peptide bonds in protein. At this level you will be testing for the presence of protein in foods. The test may also be extended to quantitatively measure the concentration of total protein. protein . ➔ Instead of the Biuret Reagent, Reagent , the following may be used •Fehling’s •Sodium

Solutions A and A  and B

hydroxide and copper (II) sulphate solutions

Procedure 1.

Add ! cm" of the liuid food sample# sample # to a clean, dry test tube

!. Add Add ! cm" of of Biuret Reagent. Reagent . Alternatively ". $se sodium hydroxide solution and solution  and copper sulphate solutioninstead. solution instead. Add % cm" of sodium hydroxide solution &'() or bench solution* and %) copper &II* sulphate solution dropwise + drop by drop  to the food sample '. $se Fehling!s A and B solutions instead. solutions  instead. -ehlings A and B should be freshly prepared. -ehling/s A is copper &II* solution and -ehlings B is a mixture of sodium potassium tartrate and sodium hydroxide solution. %cm" of each solution + A and B + should be added to the food sample. 0. 1epea 1epeatt step steps s % and and ! with with de"ioni#ed $ater to $ater  to prepare a negati%e controland control and with albumin &egg albumin  &egg white* to prepare a posti%e control. control . 2. Sha&e $ell and $ell and allow the mixture to stand for ' minutes. minutes . 3. bser%e any bser%e  any color change. * Prepare liquid samples from solid foods. 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 o n the number of tests to be conducted.

bser%ations and Interpretation

TEST

P45ITI67

97:ATI67

OBSERVATION

The solution turns from blue to violet& purple* The solution turns from blue to pin8 9o change ;The solution remains blue

INFERENCE

Proteins are present Peptides are present & Peptides or peptones are short chains of amino acid residues* 9o protein is present