Question

Find out a qualitative test for proteins, fats and oils, amino acids and 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 protein, then the colour of the reagent changes from light blue to purple.

(b) Test for fats and oils

Grease or solubility test

(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.

Item		Name of the test	Procedure	Result	Inference
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, 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.