Cornstarch Packing Peanuts:

Amylase Enzyme Action on Starch

 

Introduction:

       In this experiment you will observe the action of the enzyme amylase (-ase = enzyme) on starch. The starch source will be biodegradable packing “peanuts”,  primarily made of cornstarch, a natural plant product.  The packing peanuts are termed biodegradable because the microorganisms (“bio”) in soil produce amylase which can break down the starch that makes up the packing peanut.

Enzymes are proteins and most will be destroyed in extreme heat or pH.  The digestive enzyme, amylase, breaks down starches into simpler forms, the sugar maltose, which is soluble in water. 

             

Starch >>>___Amylase____>>> Maltose sugar

 

To detect enzyme activity of amylase, we can follow either the disappearance of starch as it is broken down by amylase (the iodine test), or the appearance of sugars (Benedict’s test) as starch is converted to sugars by the enzyme. 

To test for starch, iodine is used.  Iodine has a natural brownish color in pure distilled water.  When iodine mixes with starch in solution, positive results cause a color change that may range from avocado green to light purple to dark blue-black.    

          The common test for sugars like maltose or glucose uses Benedict’s solution.  When the clear blue Benedict’s solution interacts with low concentrations of these sugars, it turns green, yellow, or orange when heated.  High concentrations of these simple sugars produce a brownish-red precipitate.

 

Procedure:

 

  1. Pour 40 mL of distilled water into two 50mL test tubes labeled A and B.
  2. Add 3 drops of iodine into the two tubes.  Record color produced.

Tube A: ___________________  Tube B:  ____________________

  1. Divide contents of Tube A equally into 2 tubes and label A-1 and A-2.  To Tube A-2, add 1 gram of a sugar (glucose/dextrose, maltose, or coffee creamer, but not sucrose, table sugar)

Which tube serves as the positive sugar control?      _________________

Which tube serves as the negative control?              _________________

  1. Place one cornstarch packing peanut into Tube B, invert several times until dissolved.  Record any color changes. ________________________
  2. Divide the contents of Tube B equally into 2 tubes labeled B-1 and B-2.  Add 1 gram of moist soil from the school yard or flower bed to tube B-2.  Invert the tube gently to mix. Record the starting time.________

Which tube serves as the experimental tube? __________________

Which tube serves as the positive starch control?    __________________

  1. After 20 minutes record any color changes.

Tube B-1 ____________________   Tube B-2 ____________________

  1. Using a transfer pipette, place 3-4 mL of supernatant (clearer liquid on top) from each tube into 4 new empty test tubes and label accordingly.
  2. Add 10 drops of Benedict’s solution to each test tube.
  3. Using the table below, record the initial color. Place the test tubes in a boiling water bath for 3-5 minutes and record the final colors.

RESULTS:

 

 

Tube

 

Contents

 

Initial Color

 

Final Color

 

Tube A-1

 

 

 

 

Tube A-2

 

 

 

 

Tube B-1

 

 

 

 

Tube B-2

 

 

 

 

Questions

1a.  List some variables in this experiment:

 

 

1b.  Circle one of your listed variables and state whether it is a dependent or independent variable.

 

2a.  Which tube(s) tested positive for starch? ___________________

2b.  What evidence do you have that those tubes had starch in them?

 

3a.  Which tube(s) tested positive for sugar?_________________

3b.  What evidence do you have that those tubes had sugar in them?

 

4.  Summarize the purpose of the positive and the negative sugar controls:

 

 

5.  Summarize the purpose of the positive starch control:

 

 

6a.  Which tube(s) had amylase activity?______________

6b.  What is your evidence that the tube had amylase activity?

 

7.  Do you think that the amylase activity came from the living or nonliving component of soil?

 

8. Outline an experiment to test your spit for the presence of amylase: