We can identify biomolecules using a few simple lab tests:

• Proteins - Biuret Test: Add Biuret reagent; a violet colour confirms protein.
• Fats & Oils - Sudan III Test: Sudan III gives a red/orange layer if lipids are present.
• Amino Acids - Ninhydrin Test: A purple colour shows the presence of amino acids.

Testing common samples

• Fruit juice: Usually shows a positive ninhydrin test because it contains some amino acids.
• Saliva: Gives a positive protein test since it has the enzyme amylase.
• Sweat: Mostly water and salts, so tests are usually negative or very weak for proteins.
• Urine: Normally negative for proteins, fats, and amino acids (their presence usually indicates a health issue).

These quick qualitative tests help identify what biomolecules are present in everyday samples.