Describe the use of: (a) iodine solution test for starch (b) Benedict’s solution test for reducing sugars (c) biuret test for proteins (d) ethanol emulsion test for fats and oils (e) DCPIP test for vitamin C

Sourav PanNovember 14, 2024

Answered step-by-step

The following describes the use of various biochemical tests for detecting specific macromolecules in samples:

(a) Iodine Solution Test for Starch

• Purpose: The iodine test is used to detect the presence of starch in a sample.
• Procedure: A few drops of iodine solution (potassium iodide) are added to the sample.
• Result: If starch is present, the sample turns blue-black due to the formation of a complex between iodine and amylose, a component of starch. The color change indicates the presence of starch, while no color change suggests that starch is absent or has been hydrolyzed into smaller carbohydrates.

(b) Benedict’s Solution Test for Reducing Sugars

• Purpose: The Benedict’s test is used to identify reducing sugars, such as glucose and fructose.
• Procedure: The sample is mixed with Benedict’s reagent and heated in a boiling water bath for 3 to 5 minutes.
• Result: A color change occurs based on the concentration of reducing sugars:
  • Blue (no reducing sugar)
  • Green (low concentration)
  • Yellow (moderate concentration)
  • Orange (higher concentration)
  • Brick-red (high concentration) due to the formation of insoluble cuprous oxide (Cu₂O) precipitate, indicating the presence of reducing sugars.

(c) Biuret Test for Proteins

• Purpose: The Biuret test is used to detect the presence of proteins or peptides in a sample.
• Procedure: The sample is mixed with Biuret reagent, which contains copper(II) sulfate and sodium hydroxide.
• Result: If proteins are present, the solution turns from blue to purple due to the formation of a complex between copper ions and peptide bonds. The intensity of the purple color correlates with protein concentration .

(d) Ethanol Emulsion Test for Fats and Oils

• Purpose: The ethanol emulsion test is used to detect the presence of fats and oils in a sample.
• Procedure: The sample is mixed with ethanol and shaken vigorously. Then, it is added to water.
• Result: If fats or oils are present, a cloudy emulsion forms due to the dispersion of fat droplets in water. This indicates that lipids are present in the sample .

(e) DCPIP Test for Vitamin C

• Purpose: The DCPIP test is used to detect the presence of vitamin C (ascorbic acid) in a sample.
• Procedure: A few drops of DCPIP solution are added to the sample. DCPIP is blue when oxidized.
• Result: If vitamin C is present, it will reduce DCPIP from blue to colorless, indicating a positive result. The extent of color change can be used to estimate vitamin C concentration