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

In qualitative analysis, the detection of a specific compound is done from a sample. This detection is possible when the reagents used, react with the functional groups present in those compounds in a way that it would change their chemical nature in some manner.

Complete step by step answer:
Now, let us learn the names of the methods used to detect these biomolecules.
Biuret Test (Proteins): Bi means two and Uret means urea. So, the reagent is bi-urea. It is used for the detection of peptides and proteins. If the reagent is added to the sample and the colour changes from blue to purple, protein is present.
Emulsion Test (Fats and oils): The word emulsion comes from emulsification which is shown by fats and oils. What we do in this test is to dissolve the sample in ethanol and then add water to it. If positive, white clouds droplets of fats are formed at the top.
Ninhydrin Test (Amino acids): The reagent ninhydrin used, oxidizes amino acids in this test. If positive, the reagent would change from colourless to blue or purple.
Let us now look at some testing samples:
Fruit juice:
Biuret Test: Blue to purple. Protein present.
Emulsion Test: No droplets. Fats and oils are absent.
Ninhydrin Test: Colourless to purple. Amino acids present.
Saliva:
Biuret Test: Blue to purple. Proteins present.
Emulsion Test: No Droplets. Fats and oils are absent.
Ninhydrin Test: Colourless to purple. Amino acids present.
Sweat:
Biuret Test: Blue colour remains unchanged. Proteins absent.
Emulsion Test: Droplets visible. Fats and oils present.
Ninhydrin Test: Colourless remains unchanged. Amino acids absent.
Urine:
Biuret Test: Blue to purple. Proteins present.
Emulsion Test: Droplets visible. Fats and oils present.
Ninhydrin Test: Colourless to purple. Amino acids present.

Note:
- Amino acids are soluble in water. This is because they are small and have ionic free ends which help them dissolve in water.
- Globular proteins are soluble in water. But fibrous proteins are not soluble. This occurs due to the difference in their structures.
- Fats and oils are not soluble in water because they are non-polar compounds.