Purpose: To determine if a bacterium produces the enzyme amylase, which breaks down starch to glucose.
Principle: Starch Hydrolysis medium is a simple medium that contains beef extract, soluble starch and agar. Because starch is such a large molecule it cannot be directly transported into a bacterial cell. A bacterium may secrete the extracellular enzyme alpha-amylase to cleave the glucosidic linkage of starch releasing individual glucose molecules. The presence of starch can be indicated by the development of a blue color, therefore, the absence of a blue color indicates starch hydrolysis.The plate to the right illustrates the two typical reactions observed on a starch plate after the additon of iodine.
A. Starch hydrolysis as indicated by a non-blue
halo surrounding the growth (arrow).
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