I did a test with 3 solutions. I added iodine to 1% starch. Iodine to dextrin. Iodine to 5% glycogen.
Iodine in water gives yellow color.
Starch + iodine = blue
Dextrin + iodine = purple
Glycogen + iodine = dark brown/red-ish
As far as I know, starch + iodine turn blue because of its helical structure. Iodine bonds inside this helical structure. As for dextrin and glycogen, iodine will also bond, but not as easily as with starch. Dextrin and glycogen doesn't have the helical structure. So far so good?
I now heated the solution:
Starch + iodine = still blue
Dextrin + iodine = dirty yellow/not so clear yellow
Glycogen + iodine = clear yellow
So, what happened? This is my theory. Please correct me:
The helical structure didn't open, so the bond between iodine and starch didn't break.
As for dextrin and glycogen. The only thing I can think of, is that that bond between iodine and dextrin, and iodine and glycogen broke. And because of that, yellow color appeared. Just like water and iodine.
Can someone please help me out here?