Question

Name the chemical used to test starch.

Answer 1

Starch is a polysaccharide that is made up of repeating units of glucose which are joined by the help of glycosidic bonds. It is one of the most common carbohydrate components of the human diet as it is present in foods like rice, wheat, potato and maize.

Complete answer:
The word starch is derived from a German word which means strong or stiff. The physical appearance of starch is a white powder which is both odourless and tasteless. Start is made up of two types of molecules- amylose and amylopectin.
Amylose is the linear component whereas amylopectin consists of branches. The presence of starch can be indicated by means of chemical tests where a triiodide solution is used. The triiodide solution is made by mixing of iodine and iodide, the presence of starch turns the colour of the solution blue black whereas the absence does not cause this colour change.
Starch can be broken down by the help of enzymes known as amylases. Two types of amylases are widely known that act on starch- alpha amylase and beta amylase. Alpha amylases are commonly found in plants, animals as well as human saliva. Beta amylase hydrolyses starch into maltose units and is ideally used in brewing processes.

Note: Though starch is a common component of many staple foods but raw starch is not very digestible, it is digested in small amounts in the duodenum and small intestine. But when starch is cooked its digestibility increases following which it can be completely digested.