Correct Option
The correct option is A-3, B-1, C-4, D-2
Explanation
Food components such as carbohydrates, proteins, and fats are macromolecules that can be identified using specific qualitative tests. These tests rely on chemical reactions that produce distinct color changes or physical indicators to confirm the presence of specific nutrients.
Detailed Analysis
- A. Starch Test - 3. Blue-black colour: The standard test for starch involves the use of a dilute iodine solution. When iodine interacts with the helical structure of starch (amylose), it forms a complex that results in a characteristic blue-black colour.
- B. Protein Test - 1. Violet colour: The presence of proteins is detected using the Biuret test, which involves adding copper sulphate and caustic soda (sodium hydroxide) to the food solution. The copper ions react with peptide bonds in an alkaline environment to produce a violet colour.
- C. Fat Test - 4. Oily patch: Lipids (fats) are tested by crushing a small quantity of the food item on a piece of paper. If the paper develops an oily patch that becomes translucent (allowing partial light to pass through), it confirms the presence of fats.
- D. Water presence - 2. Wet hands/moisture: Many raw food ingredients contain significant amounts of water. Crushing or handling fresh vegetables or fruits often releases moisture, resulting in wet hands or dampness on the testing surface.
Key Takeaway
Diagnostic Indicators for Biomolecules:
- Starch: Iodine Solution → Blue-black colour.
- Protein: Copper Sulphate + Caustic Soda → Violet colour.
- Fat: Paper Test → Translucent oily patch.