Question

Find out a qualitative test for proteins, fats and oils, amino acids and test, any fruit juice, saliva, and urine for them.

Answer 1

Biuret test for protein: The biuret test is a chemical test used for determining the presence of peptide bonds. In a positive test, a copper II ion (Cu²⁺ ion) is reduced to copper I (Cu⁺), which forms a complex with the nitrogen and carbon of peptide bonds in an alkaline solution. A violet colour indicates the presence of proteins.

Ninhydrin test for amino acid: Ninhydrin (2,2 Dihydroxy indane-1,3-dione) is a chemical used to detect ammonia or primary and secondary amines. When reacting with these free amines, a deep blue or purple colour known as Ruhemann’s purple is evolved. Amino acid analysis of proteins is also done by ninhydrine. Most of the amino acids (including α-amino acids) are hydrolyzed and react with ninhydrin, except proline (a secondary amine). A coloured product is produced when an amino acid with free carboxylic acid and amino acid groups reacts with ninhydrin. The condensation product is yellow when the amino group is secondary.

Solubility test for fats and oils : A positive solubility test for fats is that the fat dissolves in lighter fluid and not in water. In this test, 5 drops of fat or oil are added in two test tubes containing 10 drops of lighter fluid and 10 drops cold water, respectively

Fruit juice contains sugar so it cannot be tested by the above-mentioned tests. Saliva contains proteins, mineral salts, amylase, etc., so it can be tested for protein and amino acids. Urine contains proteins, so it can be tested for it.