Question

Biuret test is used for the detection of
A Saturated oils
B Sugar
C Proteins
D Fats

Answer 1

Hint: Biuret test is a test on chemical which is helpful in confirming peptide bond in given solution after adding biuret reagent. Biuret reagents contain CuSO₄, in which Cu tends to form complexes with peptide bonds. Thus, analyse the presence of peptide bonds.

Complete Step by Step Solution:
As biuret test is used to detect presence of peptide bond, peptide bond is the bond between a nitrogen and carbonyl group like in amide such as Saturated oils or saturated fat made up of fatty acid which is long chain of hydrocarbon with sigma bonding between carbon and this hydrocarbon chain terminate with carboxylic group. Thus, there is no peptide bond in saturated oils.

Now, sugar which is a carbohydrate does not contain peptide bonds within. All the carbohydrates contain glycosidic linkage. In this linkage two carbohydrate molecules bonded with oxygen atoms in between. Thus, sugar also does not have any peptide linkage.
Peptide bond itself is present in between two amino acids. And amino acids are present in proteins. Protein consists of a large number of amino acids which make it more complex than other macronutrients. Thus, biuret test is used to detect peptide bonds and indirectly proteins.
Thus, option C is correct.

Note: After adding biuret reagent to solution, if the colour of solution changes to blue it means that protein is not present whereas if it turns solution to purple colour then protein will get confirmed. It is important to know the linkage between units of all macronutrients to predict the effect of any chemical test.