Ever wonder why apples and potatoes turn brown after cutting?

Why do apples and potatoes turn brown after cutting into them?  It all comes down to enzymes.  When cutting an apple, the apple is exposed to oxygen which reacts to two compounds.  The detailed story is in this article.

This article also tells you that the best way to slow the browning of an apple or potato is to cover the cut part with lemon or pineapple juice.