Explain Starch - Tests for the Presence of Exoenzymatic Activity?

Starch is a polymer of glucose linked together by glycosidic bonds. Microorganisms produce hydrolytic enzyme amylase which degrade starch into short polysaccharide units - dextrins and ultimately into disaccharide maltose. Maltose is finally hydrolyzed to soluble glucose molecules by enzyme maltase. Glucose is transported into the cell and is involved in cellular processes.

For observing hydrolytic activity of these exoenzymes, starch agar is used. Detection of starch hydrolysis after growth is made by observing for the presence or absence of starch using iodine. Iodine imparts blue black colour to the medium, if starch is present. Hydrolysis of starch is demonstrated by a clear zone surrounding the growth of the organism. This is a positive reaction.