Identification test for Casein: Biochemistry Practical
| S.NO. | EXPERIMENT | OBSERVATION | INFERENCE |
| 1 | XANTHOPROTEIN TEST: To 3ml of protein solution add 1ml conc.nitric acid boil for about half a minute. Cool and observe yellow colour. Now, add 2ml of conc.ammonia or 40% sodium hydroxide and observe the change in colour and after addition of alkali. | yellow colour is appears | Presence of aromatic amino acid. |
| 2 | MILLON’S TEST: To 1ml of protein solution add 1ml of 10% mercuric nitrate (prepared in 10% sulphuric acid). Boil gently for half a minute. Cool and add 3 drops of 1% solution of sodium nitrate. Mix and observe. | The red colour precipitate is obtained | Presence of tyrosine in a solution |
| 3 | SULPHUR TEST: To 3ml of protein solution add an equal volume of 40% sodium hydroxide and boil for 3 minutes. Cool and then add 1ml of lead acetate solution. | No dark grey or black precipitate is obtained. | Absence of sulphur containing aminoacid cysteine and cystine. Methionine does not answer to this test due to presence of thioether linkage which does not allow the release of sulphur in this reaction. |
| 4 | HELLER’S TEST: Take 3ml of con. Nitric | No white ring of meta proteins appears at the | Absence of protein like albumin & globulins. |
| acid and add 2ml of urine along the sides of test tube. | junction of the fluids. | ||
| 5 | PRECIPITATION BY NEUTRAL SALT: HALF SATURATION: Take 3ml of protein solution in a test tube; add an equal volume of saturated ammonium sulphate solution to it, mixed and allowed to stand. FULL SATURATION: Take 3ml of protein solution, add ammonium sulphate salt to it and keep on adding and at the same time mix till protein solution become saturated. | White precipitate is formed. No white precipitate is formed. | Presence of Protein like Globulin ,Casein. Absence of Albumin |
| 6 | NEUMANN’ TEST FOR ORGANIC PHOSPHOROUS: Take 5ml of solution add 0.5ml of 40% sodium hydroxide.Heat for one minute and cool spontaneously. Add 0.5ml of con.nitric acid and 1ml of saturated ammonium molybdate solution. | A canary yellow colour or precipitate is formed. | Presence of inorganic phosphorous. |
| 7 | PRECIPITATION AT ISOELECTRIC pH To 3ml of casein solution add a drop of bromocresol green (BCG) solution. Note the colour; add 2% acetic acid drop by drop till colour changes to light green. | Note the formation of precipitate of casein. Bromocresol green has a green colour at a pH of 4.6 which is the isoelectric point of casein | Presence of casein |
Suggested readings:
First Year B Pharm Notes, Syllabus, Books, PDF Subjectwise/Topicwise