By Emily Eggleston
For the curious thinker, the slow apple eater, and the chemistry lover, the brownness of an apple is bound to pop up. I am here to reveal the sexy truth behind the discolored fruit. A bronzed beach bod and an over-aerated apple acquire darkness by producing the same pigment. Science communicators eat your heart out.
Since you were a small child, you’ve known apples turn brown in the open air. Even with a simple chemistry background, you might guess that oxidation is the culprit. And yes, oxygen plays a role, but let’s dig deeper.
When apple flesh is exposed to air, exactly how is it that oxygen spurs the browning process? Oxygen is reacting with a particular enzyme inside of the apple that, once open to the outside world, goes into protective mode. The enzyme is called polyphenoloxidase. Once oxygen hits polyphenoloxidase, it knows the apple is in trouble because the skin has been punctured.
Scantily-clad tanned skin
The enzyme goes to work, using the new found oxygen to produce melanin. Melanin helps curb bruising for the apple and also has antimicrobial properties that prevent the spread of infection. The crisp white apple flesh slowly discolors because melanin is dark brown. Enter the beach bod. As it is exposed to sun, skin also produces melanin to protect itself. Melanin’s characteristic dark brown absorbs ultraviolet rays, so that other, more sensitive elements in the skin are spared.
Liberally slathered with lemon juice
Preventing the unsightly browning of a sliced apple has everything to do with inhibiting the enzyme’s reaction. Polyphenoloxidase only functions in certain environments. Modifying temperature and pH can successfully slow or stop the melanin production. Thus, refrigeration and lemon juice are common remedies for preserving the appealing white of a fresh apple. The highly acidic lemon juice drops the pH of the apple’s flesh below the operable range for polyphenoloxidase. Similarly, refrigeration chills the apple out of the enzyme’s ideal temperature range.
Similar phenomena in bananas, pears, mushrooms, avocados, and other foods is also explained by enzymatic browning.