SHROFF S.R.ROTARY INSTITUTE OF CHEMICAL TECHNOLOGY Subject :- OCUP Topic :- Tests Of Protein  Prepared By:- 1.Gaurav Jadav ( ) 2.Sidhdharth Parmar ( ) Guided By:- Dr. Anjali Bishnoi

Content Importance of Proteins Determination of the Protein Content of Foods Color Tests of Proteins References

Importance of Proteins Proteins are indispensable components of all living things, including the simplest forms of life, such as bacteria, algae, and other micro-organisms. They are required in the diets of all animals, including human, to synthesize tissues, enzymes certain harmones, and some blood components. In addition, they are used in the maintenance and repair of existing tissues and as source of energy for the body.

Determination of the Protein Content of Foods The analysis of protein content of foods is based on its nitrogen content. Since the average nitrogen content of protein is 16 per cent, the protein content of a substance can be obtained by multiplying its nitrogen value by a factor 100/16=6.25. For example, if a certain food contains 2 per cent nitrogen, on analysis its protein content would be 2x6.25=12.5 per cent. The total nitrogen content of proteins and peptides may be determined by the Dumas method or Kjeldahl method.

Color Tests of Proteins Proteins give a number of color reactions which serve as their test. In fact, these reactions are due to the presence of certain specific groups in the protein structure. Therefore, a given protein may not respond to all the general tests listed below. 1.Xanthoproteic Test :- When a protein is warmed with conc., a yellow color is produced. This test is given by a protein that consists of amino acids containing a benzene ring, such as tyrosine and tryptophan. The aromatic rings undergo nitration to give yellow products. Tyrosine

2. Biuret Test :- A small amount of NaOH solution is added to the protein. After mixing the two reagents, copper sulfate solution is added. Violet color is produced. Protein + NaOH + Copper sulfate = Violet Color This test is given by all proteins that contain two or more peptide linkages.

3. Ninhydrin Test :- When proteins are boiled with a dilute aqueous solution of ninhydrin, a violet color is produced. Protein + Ninhydrin = Violet Color This test is given by α-amino acids, proteins and dipeptides. GlycineNinhydrin

4. Millon’s Test :- The Millon’s reagent consists of mercury dissolved in nitric acid (forming a mixture of mercuric and mercurous nitrates and nitrites). When Millon’s reagent is added to a protein, a white precipitate is formed. Protein + Millon’s Reagent = White Precipitate This test is given by protein which yield tyrosine on hydrolysis.

5. Hopkins-Cole Test :- Concentrated sulfuric acid is added down the side of a test- tube containing a solution of protein and glyoxalic acid, to form a layer. A violet ring appears between the two layers. This test is given by proteins which have the amino acid tryptophan in its structure. Glyoxalic acid Violet Ring formed Protein

References  Organic Chemistry (Bahl & Bahl) 