Glycogen reaction with iodine

Glycogen, stored in the livers and cells of animals, is the main carbohydrate resource for animals. The molecule is built up of a large number of monosaccharide units by glucoside links. It is insoluble in water and gives a pink color upon reaction with iodine. It is broken down in the digestive system to give glucose and maltose. 

A spectrum of the color reaction of glycogen with iodine is recorded. The wavelength of the absorption maximum is positively correlated with the outer chain length of glycogen (i.e., the chain length distal of the branching points) [24]. 

Solubility.— The poly-saccharoses differ from the sugars in the absence of a sweet taste, in their non-crystalline character and in their general insolubility. Inulin and dextrin are soluble in water, glycogen is soluble to an opalescent liquid, while starch and cellulose are insoluble. In hot water starch forms a colloidal solution or emulsion, known as starch paste. Starch reacts with a solution of iodine and gives a beutifiul blue color. This is a characteristic reaction for starch and is used as a qualitative test, especially in microscopic examination. Dextrin exists in several forms, one of which known as erythro-dextrin, gives a red color with iodine. 

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