If Starch is Composed of Sugar Why Isn't Starch Sweet?

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Author: Michael Calhoun
Physical science 
Grade Level

Upper Elementary (grade 5) and/or Middle School (Grades 6-7) 

Difficulty of Project
Under $20.00 
Safety Issues

Be sure hands are dry when handling the Clinitest tablets. Avoid contact of Clinitest tablets with eyes, mucous membranes, gastrointestinal tract and clothing because sodium hydroxide and moisture produce caustic burns. Keep tablets in a well-marked, childproof bottle. Do not use any dark-blue tablets. The normal color of fresh tablets is light blue, with darker-blue flecks. During the bubbling action, hold the test tube near the top to avoid the burning of hands.  

Iodine is irritating to eyes, respiratory system and skin and stains hands and clothes. Iodine is toxic, harmful if inhaled or swallowed and the vapors may cause drowsiness and dizziness. The investigator should wear goggles, work in a well ventilated area, and follow safety precautions when using iodine.

Material Availability

The materials required for this project are readily available and inexpensive. 

Approximate Time Required to Complete the Project

1 to 2 hours to complete the activity once the materials are secured and setup. Also between 1 and 2 hours to prepare the Tri-fold board display. 


When foods containing starches are chewed in the mouth, they are mixed with saliva. Saliva contains an enzyme, (amylase) which helps chemically to change starch into small sugar molecules. Starch turns purple when added to iodine but sugar does not. The research aspect of this science fair project is to add saliva to starch to determine if indeed starch is composed of sugar.

This science fair project focuses on the use the enzyme amylase found in human saliva to break down starch into sugar, by first adding iodine to starch solution, then adding saliva, and again testing with iodine. To verify that sugar has indeed been produced the starch-saliva mixture will be tested using a commercial sugar testing agent. The results from this investigation will be displayed in a data table. 

Materials and Equipment / Ingredients

Four test tubes, test-tube rack (optional), distilled water, package of 8 oz plastic drinking glasses, spoons, safety goggles, box of saltine crackers, box of powdered starch, Tincture of iodine, and Clinitest® Reagent Tablets for urine sugar testing.

The box of saltine crackers, box of powdered starch, package of 8 oz plastic drinking glasses, distilled water, and plastic table spoons, can be purchased from the local supermarket or big box retail (Wal-Mart, Target, etc) store. The Clinitest® Reagent Tablets and Tincture of iodine are available for purchase from a drug store or pharmacy. Test tubes may be borrowed from the chemistry teacher at the local high school and are also found in toy chemistry sets. 


Starches are carbohydrates in which glucose sugar molecules are bonded together. It is a polysaccharide which plants use to store energy for later use. Foods such as potatoes, rice, corn and wheat contain starch granules which are important energy sources for humans. The human digestive process breaks down the starches into glucose molecules with the aid of chemicals called enzymes. The transformation of starch into sugar begins in the mouth. Amylase is an enzyme in saliva that will break-down starch to sugar. 

If an individual chews on a saltine cracker for a while, it will begin to taste sweet because the enzymes in saliva break down the starch into glucose sugar. Although starch is a carbohydrate, it is too big to cause a response on the taste buds. On the other hand, if the saltine cracker is held in the mouth for 15-20 minutes, enzymes in saliva will break it down to simpler sugars and sweetness will be detected on the tongue’s taste buds. 

Starchy foods are usually cooked to improve digestibility and to give it a more desirable texture and flavor. During the ripening of fruit, starch is changed into sugars, which give sweetness to ripe fruits. 

Iodine when added to starch will turn blue and therefore it can be used as a starch indicator. Clinitest® Reagent tablets are a commercial product used to test for the presence of sugars in the urine used by diabetics to monitor sugar levels. When a tablet is added to a solution that contains a monosaccharide sugar, a colored precipitate is produced. The resultant color varies with the amount of sugar present, ranging from blue (no sugar) through green to orange (concentrated sugar).

Digital photos can be taken during the experimenting process and the following websites offer down loadable images that can be used on the display board:

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