Question

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

Answer 1

(a) Test for protein

Biuret’s test – If Biuret’s reagent is added to the protein, then the colour of the reagent changes from light blue to purple.

(b) Test for fats and oils

Emulsion test - Add ethanol to a very small amount of the test substance. Shake in order to dissolve. Filter or dilute to obtain fairly clear liquid. Take another tube containing water and pour the ethanolic solution into the top. A white (milk like) emulsion indicates the presence of fats or oils.

(c) Test for amino acid

Ninhydrin test – If Ninhydrin reagent is added to the solution, then the colourless solution changes to pink, blue, or purple, depending on the amino acid.

1) Fruit juice

Biuret’s test - Fruit juice + Biuret’s reagent -Colour changes from light blue to purple. Protein is present.

Grease test - To a brown paper, add a few drops of fruit juice - No translucent spot. Fats and oils are absent or are in negligible amounts

Ninhydrin test - Fruit juice + Ninhydrin reagent + boil for 5 minutes - Colourless solution changes to pink, blue, or purple colour. Amino acids are present.

2) Saliva

Biuret’s test - Saliva + Biuret’s reagent - Colour changes from light blue to purple. Proteins are present.

Grease test - On a brown paper, add a drop of saliva - No translucent spot. Fats/oils are absent.

Ninhydrin test - Saliva + Ninhydrin reagent + boil for 5 minutes - Colourless solution changes to pink, blue, or purple colour. Amino acids are present.

3) Sweat

Biuret’s test - Sweat + Biuret’s reagent- No colour change. Proteins are absent.

Solubility test - Sweat + Water - Oily appearance - Fats/oil may be present.

Ninhydrin test - Sweat + Ninhydrin reagent + boil for 5 minutes - No colour change, the solution remains colourless. Amino acids are absent.

4) Urine

Biuret’s test - Few drops of urine + Biuret’s reagent - Colour changes from light blue to purple- Proteins are present.

Solubility test - Few drops of urine + Water - Little bit of oily appearance. Fats may or may not be present.

Ninhydrin test - Few drops of urine + Ninhydrin reagent + boil for 5 minutes. Colourless solution changes to pink, blue, or purple colour depending on the type of amino acid- Amino acids are present.