The basic unit of starch is glucose. It is composed of two units, namely amylase (15%–35%) and amylopectin (65%–85%). The structure of amylose looks like a long helically coiled unbranched chain of glucose molecules connected by α(1 → 4) linkages. The molecular weight of amylase is between 10,000 and 1,00,000. Amylose gives a deep blue colour with iodine. Basically, amylopectin is insoluble in water. The molecular weight of amylopectin varies from 50,000 to 10,00,000. Amylopectin is composed of branched chain of glucose and joined by α(1 → 4) linkages (Figure 2.12). Branching occurs through α(1 → 6) linkages between two glucose units of neighbouring chains. The branching point occurs at proper intervals, approximately 25–30 α-D-glucose units. Amylopectin reacts with iodine and gives a violet colour.