1. Composition

Monomers: Starch is a polysaccharide composed of glucose monomers.

Types: It consists of two glucose polymers: amylose and amylopectin.

2. Amylose

Structure: Amylose is a linear chain of α-D-glucose molecules linked by α-1,4-glycosidic bonds.

Properties: It forms a helical structure due to the arrangement of glucose units.

Solubility: It is less soluble in water compared to amylopectin.

3. Amylopectin

Structure: Amylopectin is a branched chain of α-D-glucose molecules connected by both α-1,4-glycosidic bonds (main chain) and α-1,6-glycosidic bonds (branch points).

Properties: It has a highly branched structure, creating a more open configuration.

Solubility: Amylopectin is more soluble in water compared to amylose.

4. Linkages

α-1,4-Glycosidic Bonds: These link glucose units along the main chain in amylose and amylopectin.

α-1,6-Glycosidic Bonds: These form branch points in amylopectin, contributing to its branched structure.

5. Molecular Weight

Size: Starch molecules can vary, ranging from a few hundred to several thousand glucose units.

Distribution: The ratio of amylose to amylopectin can affect starch’s overall molecular weight and properties.

6. Solubility

Gelatinization: Starch undergoes gelatinization when heated in water, causing it to absorb water and swell. This process disrupts the crystalline structure and increases solubility.

Retrogradation: After gelatinization, starch can retrograde upon cooling, leading to the reformation of crystalline structures and reduced solubility.

7. Iodine Reaction

Blue Complex: Starch forms a characteristic blue complex with iodine due to the iodine molecules fitting into the helical structure of amylose.

8. Function

Energy Storage: In plants, starch is a primary energy storage form.

Dietary Carbohydrate: Starch is a major source of carbohydrates in the human diet, obtained from various plant-based foods.

Understanding the chemical nature of starch provides insights into its structural properties, functional roles, and applications in biological systems and various industrial processes.