Gelatinization and Retrogradation

Starch is a polysaccharide which means containing large number of glucose units bind by glycosidic bond. Starch is mostly found in plant tissue in tubers and endosperm of seeds. Starch consists of two types of glucose polymer which are amylose and amylopectin. While amylose is a linear glucan with α[1,4] glycosidic linkages, amylopectin is highly branched glucan with α[1,4] and α[1,6] linkages. They occur together in granules but amylase may be separated from solutions because it is less soluble in organic solvents. Most starches contain 20-25% amylose.

What is Viscosity?

Viscosity is defined as the resistance of a fluid to flow. Dynamic viscosity’s unit is Pa.s in the SI system and poise (g/cm.s) in the CGS system. Viscosity varies with temperature. Because of the difference in their molecular structure, viscosity of liquids and gases changes by temperature. Viscosity of most of the liquids decreases when temperature increases. In the liquids the cohesive forces between the molecules predominates the molecular momentum transfer between the molecules, mainly because the molecules are closely packed. When the liquid is heated the cohesive forces between the molecules reduce thus the forces of attraction between them reduce, which eventually reduces the viscosity of the liquids. While the viscosity of gases increases with increasing temperature. The reason behind this is again the movement of the molecules and the forces between them. In the gases the cohesive forces between the molecules is lesser, while molecular momentum transfer is high. As the temperature of the gas is increased, the molecular momentum transfer rate increases further which increases the viscosity of the gas (Rheology).