Final answer:
Rice contains two types of starch: amylose, which is a linear, coiled polymer that contributes to starch's firmness, and amylopectin, which is highly branched and impacts the texture and digestibility of rice.
Step-by-step explanation:
The two types of starch found in rice are amylose and amylopectin. Amylose makes up approximately 20% to 25% of rice starch and is a linear, unbranched polymer consisting of D-glucose units linked by α-1→4 glycosidic bonds. Its coiled structure can produce a blue color when treated with iodine, indicating the presence of starch. Amylopectin accounts for the larger portion, 75% to 80%, with a highly branched structure. The α-D-glucose units in amylopectin are linked linearly by α-1→4 linkages with branching at α-1→6 points. This branching impacts the texture and digestibility of foods containing starch, such as rice. When rice is cooked, the starch gelatinization increases the digestibility, transforming it into a form that can readily be broken down by enzymes into sugars that provide energy.