Why Do Sliced Apples Turn Brown?

Can anything prevent an apple slice from turning brown?


My hypothesis is that an acidic solution could keep the apple slice from turning brown. The more acidic the more effective the solution will be in preventing the apple slice from turning brown.


1) Baking Sheet or Wax Paper
2) Pen or Marker
3) Tongs
4) Bowl
5) Knife and/or apple slicer
6) Olive Oil
7) Apple


1) Tear a sheet of Wax Paper for the Control and Test Specimen.
2) Label one sheet as Control and the second sheet as Test.
3) Slice an apple and use one slice for your Control and one as your Test specimen.
4) Place your Control Slice on the wax paper labeled Control.
5) Place your Test Apple Slice in a small bowl.
6) Pour Olive Oil in the small bowl.
7) Observe both apple slices every 30 minutes, taking pictures of each, and recording your results in your journal.

Research Notes

Why do apples turn brown?
  • Apples are rich in iron.
  • When the apple is cut, the knife damages cells in the apple.
  • Oxygen in the air reacts with the iron in the apple cells, forming iron oxide.
  • An enzyme called polyphenol oxidase, which is in the apple, helps make the reaction quicker.
How can you prevent an apple from browning?
  • Cut and keep apple slices under water, preventing the iron in the apple from reacting with the oxygen in the air.
  • Rub the apple slices with lemon juice. The acid in the lemon juice prevents the polyphenol oxidase from working.
  • Blanch the apple slices by placing them in boiling water for a few seconds. This will also block the browning enzyme (polyphenol oxidase).
  • You may also salt the apple slices, which also blocks the browning.
  • You may place the apples in an air tight container, which keeps oxygen from reacting with the iron in the apple slices.
Key Words used for Research:

4th Grade Science Fair project
Why do apples turn brown

Questions I wanted to answer:

1) Why do apples turn brown?
2) How do you keep apples from turning brown?
3) Why is it important to have a sample control?


1) www.education.com
2) chemistry.about.com
3) www.humantouchofchemistry.com


The Test Specimen did not brown right away, but the Control Specimen did begin browning immediately. The Test Specimen browned much more slowly, taking an additional two hours to brown.


Based on the results of the experiment, the original hypothesis was confirmed. The apple slice placed in olive oil was slower to brown than the slice that was not dipped into olive oil. If I were to run the experiment again I would use lemon juice instead of olive oil. The use of lemon juice should further prove the hypothesis since lemon juice is even more acidic. I would also merely dip the test specimen in the lemon juice and then set it out on the wax paper. During this experiment I learned the effect oxygen has on food and the chemical reaction responsible for browning our food. This reaction aids in the decomposition of our food.