Everyday science: Why do cut apples turn brown?

When the flesh of an apple turns brown, it’s due to a chemical reaction that occurs when the cells are damaged and their contents are exposed to air. This process is called oxidation — but what exactly does it mean?

First, let’s meet the players involved in the oxidation process:
 

Now, let’s look at how these players interact when we cut up our apple.

Cutting a fruit brings its flesh into contact with oxygen. Oxygen activates enzymes in the fruit's cells. These turn colourless compounds — phenols — into a brown pigment called melanin.

Is there a way to stop this from happening?

Yes! 

Enzymes can only work under certain conditions.
By blocking oxygen or making the conditions acidic, you prevent the enzymes from working. If the enzyme doesn’t work, it doesn’t transform the phenols. This keeps the apple’s flesh white!

You can achieve this by coating your apples with lemon juice, or soaking your apples in water. 

I don’t like the sound of lemony or watery apples; can I use anything else?

Yes! 

Many ingredients in our kitchen can affect the chemical conditions on the surface of the apple, and prevent enzymes from churning out melanin.

Try this fun activity to find out what else works

• Apples: Stop the Browning!

What’s the best way to store my apples, so they stay fresh?

Apples can be stored for up to eight months, in the right conditions! Visit the link below — from Agriculture and Agri-Food Canada — for science-based tips on the best way to keep your apples fresh.

• Cold storage: Making the most of your harvest 

Go Further

• Canadian scientist Dr Charles Forney's research on apples