a bananan turning brown when exposed to the air is an example of
I would guess oxydation.
Since this is not my area of expertise, I searched Google under the key words "banana browning" to get these possible sources:
https://www.google.com/search?client=safari&rls=en&q=banana+browning&ie=UTF-8&oe=UTF-8&gws_rd=ssl
In the future, you can find the information you desire more quickly, if you use appropriate key words to do your own search. Also see http://hanlib.sou.edu/searchtools/.
http://www.hackcollege.com/blog/2011/11/23/infographic-get-more-out-of-google.html
a chemical reaction called enzymatic browning. Enzymatic browning occurs when certain enzymes in fruits and vegetables react with oxygen in the air.
To understand why a banana turns brown when exposed to the air, we need to look at the components of the banana. Bananas contain an enzyme called polyphenol oxidase, or PPO for short, as well as certain chemicals called phenols. When the cells of the banana are damaged by slicing or bruising, the PPO enzyme comes into contact with the phenols and oxygen in the air. This triggers a series of chemical reactions that ultimately result in the oxidation of the phenols, turning the banana brown.
So, to answer your question, a banana turning brown when exposed to the air is an example of enzymatic browning, which is a chemical reaction between the PPO enzyme, phenols, and oxygen.