Chem 1030-010 Spring 2008

Testing for the Presence of Starch in Foods

Objective: To test the presence of starch in common foods using iodine tincture.

Introduction:

Iodine is a useful reagent to test for the presence of starch. Iodine does not dissolve in water very well so it is usually dissolved in an alcohol. One can easily buy a bottle of such a solution of iodine from grocery or drugstores and is often referred to as iodine tincture. Iodine is a reasonably strong oxidizing agent and can thus be used as a disinfectant. It has a characteristic deep brown color.

Project Procedure:

For this project you need a small bottle of iodine tincture, small amount of corn starch, bread, potato, banana, apple and any other food items you can get your hands on and to want to test.

Testing for the presence of starch:

Iodine reacts with starch to produce a deep dark blue (almost black) color. To test the cornstarch, you will need to dissolve a small amount of it in water then add a drop or two of the iodine tincture to the solution.

For bread, potatoes, etc, just add a drop or two of the iodine reagent on to the surface of the item. Observe what has happened to the color of the iodine. The darker the color the more starch there is.

Record what you observe when you add the iodine to the foods you have gathered and report either “yes” or “no” under the column that asks for the presence of starch. Do allow sometime for the iodine to soak into the foods and record the depth of color that results after a few minutes.

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Name Date

Results of Iodine Test on Different Foods
Food Tested / Observation / Starch Present?
Corn Starch /
Control Sample
Bread
Banana
Apple
Table Sugar
Carrot
Cereal
Cracker
Table Salt

Answer the following. You may use the back of this page.

Starch and cellulose are both forms of glucose, yet one is digestible and the other is not. What is different structurally about these two forms of glucose and how they link together to form these two biopolymers? See pages 436-440 of your textbook for reference. *Note - I am looking for a simple explanation of the structural differences, not an elaborate discussion. To receive full credit you must identify specifically the type of glucose that is used, and what the difference is between how they link to each other*

Continue answer to questions here:

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