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Starchy Potato Chemistry

This article appeared in the March 16, edition of the Davis Enterprise.

By Lisa Justice

Special to the Enterprise

In honor of St. Patrick’s Day, Explorit Science Center invites you to experiment with a little potato science.

Even though every modern potato can trace its ancestry back to South America, potatoes have been an important source of nutrition in Ireland for hundreds of years.  European explorers most likely brought potatoes and other New World foods back to Ireland and other European countries in the sixteenth and seventeenth centuries.

The potato is an excellent source of starch, or complex carbohydrates.  The carbohydrates in potatoes are considered complex because they contain long chains of simple sugars.  Lots of simple sugars together add up to be complex.

When you eat a potato, special proteins in your body called enzymes take these complex carbohydrates and break them down into glucose that your body can use for energy.  Just one potato can provide a lot of energy.  Let’s discover how much starch a potato can hold.

You will need a few thin slices of potato with the skin still on, iodine, a cotton swab and lots of paper towels.  Iodine can stain your skin and clothes, so you may also want to wear a pair of gloves and an old shirt.

Lay a slice or two of potato on a paper towel.  Dip the cotton swab in iodine and brush it on your potato slices.  What do you notice?  Can you describe what you see happening?  What do you think is causing it?

The iodine is having a chemical reaction with the starch in the potato.  When the iodine finds the long, straight chains of sugars in the starch, they attach to each other and get twisted.  The result looks more like a spiral than a straight chain, and it results in the purple or blue color you’re seeing.

Now examine your potato-iodine combination.  Is the whole slice turning the same color, or are some spots darker than others?  Why do you think that is?

If the spots with the most color are caused by the iodine combining with the starch, then the most colorful spots have more starch in them.  Do you see more starch in the center of your potato or at the edge?  What would happen if you tried the experiment with a slice of potato that had no skin on it?  Try it and see.

Most of the potato’s nutrients, those starchy complex carbohydrates, are stored in its skin.  So peeling the skin off of a potato will remove a lot of those starches.  The center of the potato is mostly water, so you may not see as much color change there because there isn’t as much starch.

What other foods might be high in starch?  What would happen if you tried this experiment on a carrot?  Or a corn flake?

Get creative!  Like us on Facebook to tell us what other foods you’ve experimented with or tell us your favorite way to eat a potato.


Explorit’s coming events:

• “Forces of Nature” Exhibition - open April 2 - 13, 2012 for spring break 1:00 to 5:00 p.m.  This exhibition features some of the best of Explorit’s past exhibits.

• NanoDays Festival - April 9 – 13 from 1:00 to 5:00 p.m.  Join us for hands-on nanoscale science and engineering activities and find out about the potential impact of nano science  on the future.  Events are organized by participants in the Nanoscale Informal Science Education Network (NISE Net).  


Explorit Science Center is located at 3141 5th St. and open to the public the first full weekend of every month. For more information call (530) 756-0191 or visit, or “like” us on Facebook at


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