How does iodine solution act to detect starch in test substances?
The Iodine test is used to test for the presence of carbohydrates. Iodine solution — iodine dissolved in an aqueous solution of potassium iodide — reacts with starch producing a deep purple color. This reaction is the result of the formation of polyiodide chains from the reaction of starch and iodine. The amylose, or straight chain portion of starch, forms helices where iodine molecules assemble, forming a dark blue/black color. The amylopectin, or branched portion of starch, forms much shorter helices and iodine molecules are unable to assemble, leading the color to be of an orange/yellow hue. As starch is broken down or hydrolyzed into smaller carbohydrate units, the blue-black color is not produced. Therefore, this test can determine completion of hydrolysis when a color change does not occur. Benedict’s Solution: Benedict’s reagent is used as a test for the presence of reducing sugars. This includes all monosaccharides and the disaccharides mannose, lactose and maltose. One litre o
