Class Activities

“An Apple Without A Peel”


  1. To demonstrate how an apple becomes oxidized in air and understand the process of oxidation.
  2. To investigate the action of an anti-oxidant on the browning process of an apple.
  3. To design and conduct scientific investigation.

Science Concepts:
Once the skin of the apple is removed, the exposure of apple to the air will result in oxidation of the tissues of the apple. Browning is due to polyphenoloxidase, an enzyme that causes the tannins to condense and change color. Inside the apple the polyphenol and the polyphenoloxidase are separate. Chilling to 4º C inhibits the reaction. Boiling denatures (destroys the structure and function of) the enzyme. The chloride ion will inhibit the reaction. In acidic solutions such as lemon juice, the enzyme works slowly. Ascorbic acid (vitamin C), a known anti-oxidant, can prevent oxidation.



  1. Crush a vitamin C tablet and dissolve in 100 mL of distilled water in a beaker labeled “A”.
  2. Pour 100 mL of distilled water in a beaker labeled “B”.
  3. Cut three identical wedges about 1/2 cm thick from an apple. Include the heart of the apple. Immediately after cutting, place one wedge in solution “A” and one wedge in solution “B”. Make sure all surfaces of the wedges are wet with the solution.
  4. Remove the wedges from the beakers and place all three wedges on a tray appropriately labeled.

Working in student groups of four, design an experiment based to test on of the following hypothesis or a hypothesis of your own:


  1. The greater the concentration of the ascorbic acid the longer the apple will be protected from browning time.
  2. Different varieties of apples will be affected differently.
  3. ____________(select another fruit) will not be preserved from browning.
  4. Vitamin E, another antioxidant, will work better than vitamin C.
  5. Not allowing the cut apple to be exposed to oxygen will prevent the browning.
  6. The rate of browning will increase as the temperature increases.
  7. Lowering the pH prevents the browning.
  8. Any acid will prevent the browning of the apple.
  9. Browning only occurs on the surface of the apple.
  10. __________ others

Record the time required for the first browning to occur. Record the comparative brown for 24 hours. Sketch your sample and describe where browning occurs.


Discussion of Results:


Questions for discussion:

  1. Why doesn’t applesauce turn brown?
  2. What could be another control for the teacher’s demonstration?
  3. Why don’t the vegetables in a commercially packaged ready to eat salad turn brown?
  4. What characteristic of the apple skin prevents browning of the apple?
  5. What characteristics would you genetically engineer into the apple to inhibit the browning effect?
  6. If apples normally contain vitamin C, why does it not prevent the browning?
  7. Do oranges undergo browning? Why or why not?
  8. Why were the English sailors called “limeys”?
  9. What is the RDA for vitamin C?

Recommendations for Assessment:

  1. Evaluation of lab reports that includes experimental design, data, and conclusions.
  2. Answers to questions.
  3. Conduct a class seminar – The Prevention of Browning in Apples. Have each group present their experimental results and conclude with a discussion of how some fruits can be preserved and how this lab relates to unit 3 and the oxidation processes occurring in the body.