Subjective Type

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

Solution

$$\text{Test for protein}$$
Biuret’s test – If Biuret’s reagent is added to the protein, then the colour of the reagent changes from light blue to purple.
$$\text{Test for fats and oils }$$
Emulsion test - Add ethanol to a very small amount of the test substance. Shake in order to dissolve. Filter or dilute to obtain a 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.
$$\text{Test for amino acid}$$
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.

$$\text{1) Fruit juice }$$
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.

$$\text{2) Saliva}$$
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.

$$\text{3) Sweat}$$
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.

$$\text{4) Urine}$$
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.

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