Question

The presence of protein in moong is estimated in the food product by
A. The reaction with the HCL gives red colour
B. The reaction with the iodine gives a blue colour
C. The reaction with copper sulphate and caustic soda gives violet colour
D. Both B and C

Answer 1

In any substance, peptide bond can be determined by Biuret test. This test involves reaction between the solution of protein and salt solution consisting of metal ions resulting in production of colored complex

Complete answer:
Moong beans belong to the legume family. These are low in carbs and rich in proteins. These are plant based proteins which serve as a tremendous alternative to animal proteins in case of vegetarians. Amino acids are the building blocks of proteins and there are specific sets of amino acids that contribute to a particular protein. This characteristic can serve as a basis for protein detection of protein in a provided sample. Moong beans contain nitrogen atoms in their peptide chain which interact with copper ions present in alkaline copper sulphate solution leading to dislocation of hydrogen atoms present in peptide. This results in formation of a violet colored complex. This is called a biuret test. Higher color intensity indicates that there is formation of a large number of complexes between peptide and copper ions. Also, presence of at least two peptide bonds is necessary for observing a major, quantifiable color shift with the help of these reagents.
All colour reactions are not depicted by all proteins because of their varying amino acid composition. Protein present in moong contains nitrogen containing amino acids which shows reaction with alkaline copper salts forming violet colored complexes. All other reactions are not for estimation of protein with such amino acids.
The correct answer is option “C” that is the presence of protein in moong is estimated in the food product via reaction with copper sulphate and caustic soda that gives violet color.

Note:
Biuret reaction can be used for quantitative determination of total protein by means of spectrophotometric analysis. The color intensity of the complex formed is directly proportional to the number of peptide bonds present in a reacting protein molecule.