Starch

Starch is a polysaccharide formed by a large number of D-glucose units (homoglycan). Starch is not a chemical individual, but a mixture of polymer chains with different molecular weights.

Biomedical Significance
It is the 'storage polysaccharide of plants (the exception is plants of the star family, where inulin plays the role of starch). It is stored in plants in the form of starch grains. Nutritionally, it is the 'most important polysaccharide. In humans, it is hydrolyzed by α-Amylases (salivary and pancreatic) to the disaccharide maltose.

Chemical properties
General Formula: (C6H10O5)n. It consists of two types of polymers: Amylose
 * It usually makes up about 20% of the starch grain.
 * It consists of an unbranched glucose chain connected by an α-(1→4) O-glycosidic bond.
 * The polychain forms a helix stabilized by intramolecular hydrogen bonds.
 * The helix cavity corresponds in size to the molecule iodine (I2), which gives a blue color with amylose, this property is used in the proof of starch Lugol's solution (solution I 2 in KI).

Amylopectin
 * About 80% starch grain.
 * The basic chain is the same as amylose, but unlike it, it branches every 20-30 glucose units with an α-(1→6) bond.

Physical Properties
In cold water, it forms colloidal solutions (only the amylose part is soluble; amylopectin does not dissolve, but swells). Compared to an identical number of free molecules, glucose is osmotically 'inactive.

Resources
Cereals, potatoes and other plant parts commonly found in food.

Related Articles

 * Glucose
 * Polysaccharides