The iodine test is a qualitative test used to detect the presence of a polysaccharide called starch.
The starch is made up of two units, amylose, and amylopectin.
Amylose in starch is responsible for the formation of dark blue color with iodine solution.
Amylose forms a helical structure and iodine slips inside this and forms deep blue color.
Amylopectin has a linear structure and forms a reddish-purple color with iodine solution.
The principle behind the experiment is that the polyiodide ions form a colored complex with helical chains of glucose residue of amylase (deep blue), dextrin (black), or glycogen (reddish-purple).
