write the detecting test for protein
Answers
Answer:
Biuret TestThe formation of violet colour confirms that the proteins are present.Xanthoproteic TestThe yellow coloured solution that appears confirms the presence of the proteins.Millions TestThe brick red colour solution confirms that the proteins are present.
Explanation:
Proteins are the main constituents of all living cells and are the building blocks of life. They play an essential role in the growth and development of cells and tissues. Proteins have a high molecular mass, long chain polymer, composed of α-amino acids and contain carbon, hydrogen, nitrogen, oxygen and sometimes phosphorus and sulfur.
The following are the simple tests carried to find the presence of proteins in the given food samples.
Biuret test
The compounds with peptide linkage undergo this test. Proteins are polypeptides of amino acids linked together by peptide bonds. An alkaline solution of protein is treated with a drop of aqueous copper sulfate and a bluish violet color is obtained.
Note: Formation of violet coloration confirms the presence of Proteins.
Xanthoproteic test
Proteins on treatment with nitric acid give a yellow or orange color. Concentrated nitric acid is used for nitration. On the treatment of nitric acid, proteins give yellow precipitate which turns to orange color on treatment with alkali.
Note: The appearance of a yellow color solution confirms the presence of proteins.
Millions test
Phenolic group of tyrosine of proteins reacts with mercuric sulfate in the presence of sodium nitrite and sulfuric acid to give red color. Millon’s test is given by proteins containing phenolic amino acids. Gelatin does not give this test. First, a white precipitate is formed when proteins are treated with millions reagent and then turns to brick-red color on boiling, this confirms the presence of proteins.
Note: The appearance of brick red color solution confirms the presence of proteins.
Ninhydrin test
Proteins react with pyridine solution of ninhydrin and change to a colored solution from a deep blue to violet-pink or sometimes even to a red color. Ninhydrin solution is prepared by dissolving 0.1gm of ninhydrin in about 100ml of distilled water. But this solution of ninhydrin is unstable and can be kept for two days.
Note: The appearance of violet color solution confirms the presence of proteins.