Which of the following carbohydrates develops a deep blueback colour on treatment with iodine solution?

Options

A. Amylose
B. Amylopectin
C. starch
D. Both (1) and (3)

Answer

D

Explanation

A room temperature, starch gives a deep blue-black color, on addition of `I_(2)`. The color changes to reddish-brown when the test is performed at elevated temperatures. Thus, starch can be used for the detection of traces of `I_(2)` generated in a reaction.
Amylose in starch traps `I_(2)` molecules its helix, forming a charge-transfer complex with the characteristic blue-black color. At higher temperatures the helix partially unwinds and fewer `I_(2)` molecules are trapped. Upon cooling, the helix reforms, enclosing the `I_(2)`, and the original color returns.
Amylopcetin gives a less intense red-brown color because the helical structure is disrupted by the branching of the chain.