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Testing For Starch

based on 4 ratings
Author: Keren Perles

Grade Level: 6th - 8th; Type: Chemistry

Objective:

This science project will demonstrate how starches are converted to sugar during mastication and salivation.

Research Questions:

  • How can you test a food for starch?
  • How do chewing and salivating help with the digestion process?

Many of the foods you eat are made up of starch. Starch molecules are large, though, and need to be broken down in order to be digested. In this science project, you will examine just what happens during the salivation and chewing processes.

Materials:

  • Plastic gloves
  • Safety goggles
  • Tincture of iodine
  • Water
  • Eyedropper
  • Cup
  • 2-3 identical crackers
  • Several plates or saucers
  • Cooked potato
  • Cornstarch
  • Measuring spoons
  • Glucose testing strips (e.g., Diastix), optional

Experimental Procedure:

  1. Put on your plastic gloves and safety goggles.
  2. Mix 10 drops of tincture of iodine with 30 drops of water to make an iodine solution.
  3. Put a cracker on a plate, and test it for starch using a drop of the iodine solution.
  4. Chew a second cracker for 60 seconds until it is completely mixed with saliva. Spit out the chewed cracker onto another plate, and add a drop of iodine. You may be surprised to observe that the iodine no longer changed colors. The process of chewing the food and mixing it with saliva breaks down the starches in the cracker and converts them into sugars.
  5. Use this process to test other starchy foods, such as a cooked potato. Does chewing the cooked potato have the same effect as chewing the cracker?
  6. Put two small piles of cornstarch, containing ¼ teaspoon each, on another plate.
  7. Use the dropper to remove some saliva from your mouth. Put at least ten drops of saliva on one of the cornstarch piles and mix it around.
  8. Test both piles with the iodine solution. Does simply adding saliva turn the starch into sugar?
  9. If you’d like, you can add a teaspoon of water to each of the above foods and test them for sugar using a glucose stick (such as the type diabetics use to test their urine).

Terms/Concepts:

  • Which foods contain starch?
  • What are the first several steps of the digestion process?
  • How are sugars and starches related?

References:

  • Easy Genius Science Projects with Chemistry, by Robert Gardener. Pp 95-96, 101.
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