Polysaccharides
Polysaccharides contain a large number of monosaccharide units joined together by glycosidic linkages. They mainly act as the food storage or structural materials.
Starch
- Main sources of starch are wheat, maize, rice, potatoes and barley.
- It is a white amorphous powder, in-soluble in cold water.
- It is a polymer of α-glucose and consists of two components- Amylose and Amylopectin.
- Amylose: It is a linear polymer of α‒ glucose. It is water soluble and gives blue colour with iodine solution.
- Amylopectin: It is a branched chain polymer of α‒ glucose. It is water in-soluble and does not give blue colour with iodine solution.
Cellulose
- Cellulose is a linear polymer of β-glucose. It consists of bundles of polymeric chains which are held together by hydrogen-bonding.
- Main sources are wood (45 –50%), cotton (90 – 95%). It is the main constituent of cell walls.
- It is colourless amorphous solid that decomposes on heating.
- It does not reduce Tollen’s reagent or Fehling’s solution.
- It cannot be digested by human stomach.
- Cell wall of bacteria and plants is made up of cellulose
- Cellulose forms a number of important products, such as:
- Cellotape used for packaging.
- Viscose rayon used in textile industry.
- Gun cotton used as an explosive.
Glycogen
- The carbohydrates are stored in animal body as glycogen. It is also known as animal starch because its structure is similar to amylopectin and is rather more highly branched.
- It is present in liver, muscles and brain.
- When the body needs glucose, enzymes break the glycogen down to glucose.
- Glycogen is also found in yeast and fungi.