The hydrolysis of starch was stopped when the iodine test no longer gave a blue color. Does this mean that the starch solution was completely hydrolyzed to glucose?
In this experiment, we will work with the enzyme amylase. This enzyme is
responsible for hydrolyzing starch. In the presence of amylase, a sample of starch will be
hydrolyzed to shorter polysaccharides, dextrins, maltose, and glucose. The extent of the
hydrolysis depends on how long it is allowed to react – if the starch is hydrolyzed
completely, the resulting product is glucose.
You will test for the presence or absence of starch in the solutions using iodine
(I2). Iodine forms a blue to black complex with starch, but does not react with glucose. If
iodine is added to a glucose solution, the only color seen is the red or yellow color of the
iodine. Therefore, the faster the blue color of starch is lost, the faster the enzyme amylase
is working. If the amylase is inactivated, it can no longer hydrolyze starch, so the blue
color of the starch-iodine complex will persist.