Starch is a polymeric carbohydrate that is composed of numerous glucose monomers. It is an organic substance that is produced by all the green plants and is stored as reserve food in chloroplasts.
Given below is the molecular structure of starch.
Starch – Diagram
Structure & Features
- The molecular formula of starch is (C6H10O5)n.
- It is composed of n number of glucose monomers joined by ɑ (1,4) linkage in chains and ɑ(1,6) linkages at branching point.
- Two glucose molecules combine together to lose one molecule of water (H2O) for the formation of a starch polymer.
- Starch molecules exist in two forms – a simple linear polymer called amylose and a more complex branched form called amylopectin.
- Amylose is a linear polysaccharide chain that is made up of glucose monomers joined by ɑ (1,4) glycosidic linkage. Amylose makes upto 30% of the total starch molecule. It has a helical structure and is more resistant to digestion.
- Amylopectin is a highly branched polymer made up of glucose subunits. It is made up of linear chains of glucose units that are linked by ɑ (1,4) glycosidic linkage along with a number of side chains that branch the structure by ɑ(1,6) glycosidic linkages.
- Amylopectin makes upto 70% of the starch molecule. It is insoluble in water.
- Physically, starch appears as a white, odourless and tasteless powder.
- It is insoluble in both water and alcohol.
- It is the most common form of energy storage in plants.
- In plants, starch is also stored in storage organs like roots (cassava plant), tubers (potato), stems (sago plant) and seeds (wheat, rice and corn).
- This starch can be broken down by a certain set of enzymes when required by the plant into glucose monomers and is supplied through diffusion across the plant tissues.
- Starch polymer is one of the most important components found in the staple diet of humans in the form of cereals and root vegetables.
Commercial Uses
- Commercial starch is extracted from the roots and tubers of tapioca, sago, wheat and potato plants.
- It is used as a thickening agent in baking goods and confectionaries.
- It is used in the manufacturing of paper to increase its strength.
- It is also used to make tape, paper boxes and bags, gummer paper and corrugated paperboard.
- It also finds its use in the textile industry during warp sizing that imparts strength to threads at the time of weaving. ‘
- It is also used in pharmaceuticals as a binding agent, as an excipient and tablet disintegrant.
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