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Apples: Turning Brown After Being Cut - Causes and How to Prevent

Apples: Turning Brown After Being Cut - Causes and How to Prevent

You get some apples, they look great and feel firm.  You take them hom,e, slice them up and turn around and they're brown!  What happened?

Causes of apple browning when cut

This is called  "enzymatic browning." When you cut open an apple, the flesh is now first exposed to oxygen. An enzyme in the apple called polyphenol oxidase (PPO) starts to  oxidize compounds in the apple's flesh called polyphenols.

The oxidized polyphenols are transformed into "o-quinones" , which then react with amino acids in the apples to produce the brown color.

This enzymatic browning also occurs in other fruit, most noticeably bananas, pears and eggplants.

Effects?

The browning does not affect flavor or even texture.  Sure, if you leave cut apples out for a day, that would, but that's due to actual rotting, not a simple enzymatic color change. An apple that brows after being cut is still fine to eat, and if you were blindfolded, you couldn't tell the difference.

How long does it take to brown?

At right are soime time-lapse photos of a Fuji apple slice after being cut.  Within 10 minutes, it is already browning. 

Notice that it mostly peaks at 20 minutes and doesn't get much worse after that.  Even 2 hours later, there is just light browning on the surface of the cut.

That's not to say that all apple varieties will behave exactly the same. Some apple varieties have more of the enzymes and the polyphenols which means they brown more.  Some new varieties have been bred to have lower levels of these compounds and stay white after cut.

What to do to stop browning

If you want to keep enzymatic browning to a minimum, see this page for simple tips that work!