Digestive enzymes in saliva begin breaking down starch into simple sugars in our mouths. Soda crackers are mostly starch. As you chew a soda cracker, the enzymes in your saliva begin to break down the starch into sugars. Benedict's solution is an easy way to test for glucose, a simple sugar. Benedict's solution is blue with no glucose present, yellow with a slight amount of glucose present, orange or green with a medium amount of glucose present, and dark red with much glucose present. Test a soda cracker for starch with a drop of iodine solution. The blue-black color indicates starch is present in the cracker.
OBJECTIVES
Investigate the effect of saliva enzymes on the digestion of starch.
These materials are needed:
soda crackers
Benedict's solution
4 test tubes
beaker or small saucepan
burner; either a stove burner, an alcohol lamp, or a Bunsen burner
Procedure: (View and print a copy of the procedure.)
Start a water bath and heat it to a very gentle boil. This may consist of a beaker 1/2 full of water heated by an alcohol lamp, Bunsen burner, or small saucepan 1/2 full of water heated on a stove burner.
Pour about 1/4" (or about 3 ml) of Benedict's solution into each of four test tubes. Mark these test tubes as "1", "2", "3", and "4" with a black crayon or pencil.
Finely crush 1/4 of a soda cracker. Mix the crushed cracker thoroughly with a little water until it becomes a paste. Pour this cracker-water mixture into test tube #1. Cover the test tube with your thumb, and shake it well.
Rinse your mouth well with water. Chew 1/4 of a soda cracker in your mouth for about 5 seconds, and then spit the cracker into test tube #2. Cover the test tube with your thumb, and shake it well.
Rinse your mouth well with water. Chew 1/4 of a soda cracker in your mouth for about 30 seconds, mixing it well with saliva, then spit the cracker into test tube #3. Cover the test tube with your thumb, and shake it well.
Rinse your mouth well with water. Chew 1/4 of a soda cracker in your mouth for about 60 seconds, mixing it well with saliva, then spit the cracker into test tube #4. Cover the test tube with your thumb, and shake it well.
Place all 4 test tubes in the hot water bath for about 3 minutes or until they just begin to boil. Carefully remove the test tubes from the water bath and note the color of each. Based on the color changes, which test tube had the least glucose present? Which one had the most glucose present? Why?
Carefully note the color changes in each solution sample:
No Saliva
Chewing 5 seconds
Chewing 30 seconds
Chewing 60 seconds
As you chewed the cracker longer, what happened to the amount of starch left in the cracker?
As you chewed the cracker longer, what happened to the color of the solutions?
Benedict's solution is a test for a simple sugar called glucose. The more red the color, the more glucose that is in the test substance. What does this investigation show?
