Apple Oxidation

Here's what you'll need...
  • Tray
  • Apple slices
  • Vinegar
  • Water
  • Baking Soda and water mixture
  • 4 Pipet

Autumn is upon us and so is apple season. Hurrah! This is the season to eat fresh apples from the orchard and to bake apple cake, apple pie, apple sauce, apple crisp, ect. Whenever I bake with apples or slice apples for my lunch, I always have a problem with the apples turning brown.

This browning is due to oxidation. Oxidation is a process that happens when oxygen molecules come into contact with contact living tissue or metal. Yet, technically, with the discovery of electrons, oxidation is more precisely defined as the loss of at least one electron when two or more substances interact. Those substances may or may not include oxygen, but in our experiment, exposure to oxygen IS the cause of browning. Oxidation is the same process that causes iron to rust and copper to turn a greenish tint.

In our experiment we will try to lessen the effects of oxidation. We will gather a few household chemicals for our experiment, apply these chemicals to our apple slices, let them sit, and then make our observations.

For my chemicals, I chose to use water, vinegar, lemon juice, and baking soda mixed with water. After you gather all of the materials, cut the apple. You want the fruit to be as fresh as possible. Now put 3-4 droplets of each chemical over the mantel (the white inside of the apple). I chose to label each apple slice with the chemical name which I was applying. Let the apples sit. The more exposure to air the mantel receives the browner it becomes. After an hour I came back to my apple slices and made my observations.

We can clearly see in the video that the apples covered in water and baking soda were both very brown. Water and baking soda did very little to halt to slow the oxidation process, with the oxygen molecules in both chemicals oxidation was most likely aided. The vinegar apple was a little less brown then the first two, while the lemon juice apple was nearly all white. Vinegar and lemon juice are both acids. The acidity seems to have made all the difference in delaying browning.

The acidity of the lemon juice lessens the oxidation reaction The slowing of browning is due to the presence of ascorbic acid (vitamin C) in the lemon juice. The ascorbic acid reacts with oxygen contained in air, not allowing it to attack the apple. Therefore, when you want to preserve a fruit (apple, pear, banana), you should wet the exposed surface in lemon juice.

Now, when you cut your apples for baking or eating watch the rate at which they brown. Add a couple drops of lemon juice. This will not only give a hint or flavor but also slow oxidation and keep your apples looking fresh.

Try this experiment at home with different chemicals. Instead of lemon juice, try orange juice. Or replace vinegar with vinegar with vegetable oil. Let us know what your results are. We look forward to hearing from you!