The Oxidation of an Apple

A chemistry essay on the oxidation of an apple.

 When an apple’s skin is pierced and then left out in the air, then quickly it will turn from its beautiful fleshy white colour to a soggy brown colour. The flesh of the apple is being oxidized in the air, and thus the process is called oxidation. The oxidation of an apple is a very similar reaction to the rusting of iron with the air. This form of oxidation actually uses oxygen as its oxidizing agent, but that is not always the case. Oxidation is defined as the loss of electrons. For the loss of electrons to occur, there must also be a subsequent gain of electrons, as the electrons cannot simply float off into nothing. That process is called reduction.

In apples, the specific enzyme that causes the brownish colour to appear is called polyphenol oxidase (PPO).1 This enzyme is found in many other things, including noodles, breads, and chapattis, and is has the same browning effect in the other things as well. The enzyme exists inside the cell. When the cell is broken it releases the enzyme, which then reacts with the oxygen in the air and forms a layer on the outside. For the cell to be broken, in the apple’s case, the apple’s skin must be pierced or broken by an outside force. The skin is what protects it from turning into mush while it is growing. 2

Shown below is a diagram of the chemical reaction that takes place. In this diagram it only uses a monophenol as opposed to a polyphenol as well. The monophenol reacts with the oxygen in the air, which creates diphenol. And so forth. When the complex reaction is complete, what is left are complex brown polymers. This is what is seen as the “brown stuff” when an apple skin is pierced. The diphenol is being reduced by the o-quinone, which in turn is the molecule that is being oxidized. 1

So when an apple is turning brown, what is actually happening is the small molecules in each of the individual cells are reacting with the oxygen in the air, and forming a layer of stuff on the top that is brown. It does not make it harmful to eat, just slightly soggy.

1. Pollick, Michael (2003). What is oxidation?. Retrieved January 12, 2009, from WiseGeek Web site: http://www.wisegeek.com/what-is-oxidation.htm

2. N/A, (2007, July 30). Why do apple slices turn brown after being cut?. Retrieved January 13, 2009, from Scientific American Web site: http://www.sciam.com/article.cfm?id=experts-why-cut-apples-turn-brown

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24 Responses to “The Oxidation of an Apple”
  1. jhon Says...

    On March 19, 2009 at 4:31 pm

    this suckz


  2. big rob the 2nd Says...

    On April 14, 2009 at 7:28 am

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  3. noah Says...

    On August 8, 2009 at 11:21 pm

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  4. matteo Says...

    On December 7, 2009 at 3:52 pm

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  5. dapo Says...

    On December 8, 2009 at 12:50 pm

    really helpful thank you


  6. saf Says...

    On February 24, 2010 at 6:57 am

    thnks


  7. trev. Says...

    On April 16, 2010 at 8:56 pm

    brown apple skin is apparently helpfull for diorhea.why or how??


  8. trev Says...

    On April 20, 2010 at 5:12 am

    good answer world . still calculating are we ? hope so. hope to hear from someone who can explain,cheers.


  9. A.J. Says...

    On September 26, 2010 at 12:58 pm

    this website really helped me with my research paper. thanks a lot!


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    On October 6, 2010 at 11:35 am

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  14. kmbrunskill Says...

    On October 6, 2010 at 11:38 pm

    haha..

    thank you for the lovely comments!


  15. h Says...

    On December 15, 2010 at 7:41 pm

    bc


  16. bert Says...

    On January 5, 2011 at 12:12 pm

    I find an apple oxidizes much faster in Beijing, China rather than back home in the US. In the US there are at least several minutes before I notice the browning but in Beijing it is not minutes at all but literally seconds. I find in less than a minute the browning becomes obvious. What could be the reason for this? I know there is far less pure oxygen in Beijing than back home. The pollution here is ridiculous.


  17. Alyssa Says...

    On March 23, 2011 at 1:10 pm

    i needed this thnx


  18. Ellie Says...

    On November 28, 2011 at 12:38 am

    This was incredibly helpful. I actually did my Science Fair project on this. Thank you sooo much! xx

    Ellie M.


  19. morgan Says...

    On January 23, 2012 at 5:09 pm

    THANK YOU :) ))


  20. Carolinka Says...

    On February 8, 2012 at 9:07 pm

    Thank you very much, does the oxidation differ on different types of apples?


  21. Jermaine Griffin Says...

    On May 21, 2012 at 1:43 pm

    thanku i needed this infromation.


  22. aarvan Says...

    On October 17, 2012 at 10:37 am

    will apple skin also get oxidised like the pulp ?


  23. kpa Says...

    On February 22, 2013 at 10:21 am

    aples are so fuckd up.i love the imformation but i hate the topic!!!!!!!!!!!!!!who wrote this is a hour


  24. Abbie R. Says...

    On February 23, 2013 at 5:43 pm

    Thanks! This helped a lot with the background research for my Science Fair Project. It really breaks the info down into simpler terms so I actually understand it.


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