Why when iodine and saliva and bread crumbs is added turns to purple?

When iodine is mixed with saliva and bread crumbs, it turns purple due to the presence of starch in the bread. Iodine reacts with the starch molecules, forming a blue-black complex, which can appear purple depending on the concentration and lighting. Saliva contains enzymes that begin to break down starch into simpler sugars, but the iodine interaction is primarily with intact starch. This color change is a common test for the presence of starch.