MadSci Network: Chemistry

Re: Why would one apple-type brown faster than another?

Date: Fri Jan 29 19:21:48 1999
Posted By: Carol Crouse, , Food Technology, The Food Chain Ltd.
Area of science: Chemistry
ID: 916632967.Ch

Dear Jessica - 

You are an observant young scientist!

This browning reaction that you've noticed after you cut an apple is caused 
by enzymes in the apple.  Enzymes are chemicals that are produced by living 
cells - within humans, animals and plants - and are responsible for most of 
the reactions that take place within the living organism.  For example, 
humans have different types of enzymes in our saliva and in our digestive 
tracts that help us digest different types of food (proteins, starches, 

For the browning reaction to take place in the apple, three things are 
needed: 1)the enzyme called phenolase,
        2)the target for the enzyme - phenols, and
        3)oxygen (just like your Dad said).

You can always recognize an enzyme because they end in "ase", with the 
first part of the word referring to the target that the enzyme will attack. 
Therefore, you know that phenolase attacks phenols, protease attacks 
proteins, etc.

Back to the three things needed - some types of apples turn brown faster 
than others because they have more or stronger phenolase in them.  In whole 
apples, the phenolase and phenols are kept separated but when you cut or 
bite the apple, the apple cells are opened and the enzyme and target can 
then mix together.  The enzyme then changes the phenols into different 
chemicals that happen to be yellow or brown and it is the color of these 
new chemicals that you see.

One other thing that can make apples brown faster is warmer temperatures.  
Your cut apple in California is going to brown faster than mine in Canada - 
at least on this January day. 

There are some ways to stop the enzyme from making your apple or banana or
potato turn brown.  

You know that oxygen is needed for the change, so you can try to keep 
oxygen away from the cut fruit.  Cut an apple or potato in three pieces.  
Leave one out in the open, put one piece in a bowl of water (so the water 
covers it) and put the last piece in a plastic bag that you suck the air 
out of with a straw and then fasten with a twist tie.  Check them later on 
to see which piece is still the whitest.

Though enzymes like warm temperatures, they are destroyed by hot 
temperatures so if you cook the apple or potato, even for just a minute in 
the microwave or in boiling water, it is enough to stop the enzymes that 
would make the surface turn brown.

Another way to stop the enzymes is by using some acid.  There are lots of 
useful acids in common foods - in vinegar, oranges, lemons. Next time mix 
some of your apple slices with some orange slices, stir them so that the 
orange juice coats the apple and the apple will not turn brown.  

So now, Jessica, you know that apples contain phenols and phenolase.  
Different varieties of apples contain different amounts of phenolase and 
that is the main reason why some turn brown faster than others.

Enjoy your apples!

Carol Crouse
Food Consultant
The Food Chain Ltd.

Current Queue | Current Queue for Chemistry | Chemistry archives

Try the links in the MadSci Library for more information on Chemistry.

MadSci Home | Information | Search | Random Knowledge Generator | MadSci Archives | Mad Library | MAD Labs | MAD FAQs | Ask a ? | Join Us! | Help Support MadSci

MadSci Network,
© 1995-1999. All rights reserved.