Question

What is starch? Write short notes on it.

Answer 1

Starch is an example of saccharides (polysaccharides). So to understand Starch, lets understand first what polysaccharide is. So, the saccharide which on hydrolysis gives or forms a large amount of monosaccharides are popularly called polysaccharides.

Complete answer:
-Starch (can also be termed as amylum) is a type of polymeric carbohydrate which consists of a large number of glucose units that are joined by glycosidic bonds. These polysaccharides are produced by most of the green plants as an energy storage. It is also one of the most common carbohydrates in the human diet. It is contained in a large amount in staple foods such as potatoes, wheat, cassava etc.
-Starch has a more complex structure than that of cellulose. It is completely insoluble in cold water but if we do grinding and soaking then it makes them to form a colloidal solution. Also, when we perform the partial hydrolysis of starch and glycogen then it will produce the disaccharide maltose and a very low molecular weight dextran.
-By doing the hydrolysis of starch, it will yield two fractions. Around $20$ of the total hydrolysed product is soluble in water and the material is called amylose. Amylose is considered to be a linear chain of several thousands of glucose units that are joined using alpha $C-1$ to $C-4$ glycosidic bonds. Also, the amylose solutions are the colloidal dispersions of hydrated micelles.

Note:
Most of the starch is of high molecular weight substance, consists of around a million glucose units and these are called amylopectin. The molecules of amylopectin is a network of branched glucose units in addition to a linear chain connected using $C-1$ to $C-6$ glycosidic links.