Question

1. Explain why cornstarch is used for thickening. The explanation should connect to what you know about the structure of amylose and amylopectin.

Answer 1

Cornstarch is the endosperm of corn kernels that has been dried and ground. Corn starch is used as a thickening agent It is sometimes preferred over flour because it forms a translucent mixture, rather than an opaque one. As the starch is heated, the molecular chains unravel, allowing them to collide with other starch chains to form a mesh, thickening the liquid The thickening process is called gelatinization. Starch gelatinization is a process that breaks down the intermolecular bonds of starch molecules in the presence of water and heat, allowing the hydrogen bonding sites (the hydroxyl hydrogen and oxygen) to engage more water.Starch or amylum is a carbohydrate consisting of a large number of glucose units joined together by glycosidic bonds. Starch consists of two types of molecules: the linear and helical amylose and the branched amylopectin. Depending on the plant, starch generally contains 20 to 25% amylose and 75 to 80% amylopectin.

CH,OH 내애 он -01 on OHT300-60 OH structure of any lose molecule. CH, OH CHOH Oºn ON CHOH Oy structure of amplopectina ےے

Straight chain amylose molecules tend to line up parallel to each other in solution. As the solution cools, there is less energy available to keep the molecules apart. The hydroxyl groups on parallel amylase molecules exert attractive forces and the molecules are pulled together which is known as gelatinization.