The test tubes were then heated over a Bunsen burner until warm. Students watched for any color change and recorded them. Time for clean up. Starch digestion begins in the mouth with enzymes that are secreted in saliva. You add a drop of iodine solution, and it produces a dark blue color, indicating the presence of starch.
Enzymes are proteins.
Temperature can effect them. It is denatured. Enzymes must fit with their substrate in order to work. If an enzyme is denatured, it cannot fit anymore. An enzyme that cannot fit, cannot do its job.