Why does starch gives blue color with iodine while its main component AMYLOPECTIN gives red color with iodine?

Question

Starch is a storage polysaccharides. It has 2 components, one is amylose and the other one is amylopectin. There is 15-20% amylose which gives blue colour with iodine and 80-85% amylopectin which gives red colour with iodine. Though the major component AMYLOPECTIN gives red colour with iodine, starch gives blue colour in iodine. Why so?

Answer 1

webexhibits.org has a very nice explanation of the mechanism of the starch-iodine test that will help you answer this question.

Connie