Question

if any food item gives blue-black colour with iodine then which nutrient is present in it ??​

Answer 1

Explanation:

starch

If iodine is added to any food item and it causes thefood item to turn to a blue-black colour, it indicates the presence of the nutrient called starch (carbohydrate).

Answer 2

The Iodine test is used to detect the presence of starch like carbohydrates in food components.

• The iodine test detects the presence of starch by causing the sample to turn blue-black after a few drops of potassium iodide solution is added to it. It adheres to the starch's helical rings.
• The production of polyiodide chains from the reaction of starch with iodine yields the reaction in the iodine test.
• Amylose, found in starch, forms helices around which iodine molecules cluster, resulting in a dark blue or black colour.
• The blue-black colour is not produced when starch is hydrolyzed into small carbohydrate units.
• As a result, even if no colour change occurs, this test can suggest that hydrolysis is complete.
• With increasing temperature and the addition of water-soluble organic solvents like ethanol, the colour intensity decreases. Because starch is hydrolyzed at a very low pH, the test cannot be performed.
• Because of the development of an intermolecular charge transfer complex, Starch transforms to a deep "blue-black" colour when aqueous solutions of the triiodide anion are added.