Dear christineg,
Apples decompose much faster if they are cut open than if they are left whole.
To see why this is so, consider the mechanism by which an intact apple
matures. The apple breathes, as it were, through its peel. It takes in
oxygen and converts it to carbon dioxide, which is in return released
through the peel. The conversion of oxygen to carbon dioxide causes
the cells of the apple to decompose. This is oxidation, the same
process whereby cars rust and eventually fall apart. Similarly, during
the oxidation of an apple, its starch decomposes into sugar, which
decomposes further into organic materials.
Since the oxidation of an intact apple is mediated by its peel, the
pores of which admit only a very few oxygen molecules at a time, the
apple decomposes very slowly. Under the right conditions, an intact
apple can be kept in storage for as long as a year.
"Apples take in oxygen and give off carbon dioxide as starches in the
flesh change to sugar. [...]
"CA storage is a non-chemical process. Oxygen levels in the sealed
rooms are reduced, usually by the infusion of nitrogen gas, from the
approximate 21 percent in the air we breathe to 1 percent or 2
percent.
"When the proper growing and harvesting techniques are used, many
varieties of apples can store for 12 months or longer in CA."
Best Apples: Facts: Controlled Atmosphere Storage (CA)
http://www.bestapples.com/facts/controlled.html
In contrast, a cut apple exposes a large area of its flesh directly to
the air, without the protection of the peel. This allows the cells in
the apple flesh to interact at a much higher rate with the air,
absorbing oxygen much faster and releasing carbon dioxide much faster.
The result is rapid decomposition. An apple that has been cut into
slices will last, if left untreated, at most two weeks before it
becomes inedible.
"Apples discolour or turned brown when peeled or bruised and exposed
to air. This discolouration or browning is due to oxygen, O2, reacting
with chemicals released, breaking down the cells in the fruit. The
reaction is called enzymatic oxidation as it is a process catalysed by
the enzymes present in the apples."
University of Bristol: School of Chemistry: Browning Apples
http://www.chm.bris.ac.uk/webprojects2003/lim/Appleweb2003/applechemistry.htm
"Some produce poses a more formidable challenge to the fresh-cut
industry; two examples are the all-American favorites: apples and
potatoes.
"Cut an apple or a potato and see how long it takes before it turns
brown. You won't have to wait long. [...]
"How do you prevent browning in a fresh-cut apple with a shelf life of
five to 14 days?"
Food Product Design: Suanne J. Klahorst: Keys to Fresher Produce
http://www.foodproductdesign.com/archive/1998/1198nt.html
Recent advances in food preservation have made it possible to extend
the shelf life of a cut apple to as much as five weeks.
"[R]esearchers at the U.S. Department of Agriculture in Beltsville,
Md., claim they have been able to prevent the browning of cut apples
for five weeks under "normal atmospheric conditions," a significant
jump over the current five to seven day shelf life for most cut fruit
that has been treated against browning."
Science Daily: Apple Browning Significantly Delayed In USDA Tests
http://www.sciencedaily.com/releases/1999/01/990113074812.htm
However, treated apple slices are still far from matching the shelf
life of intact apples.
To recapitulate, an apple left whole oxidizes slowly because its peel
moderates the rate at which oxygen reaches the flesh. If cut, the
apple flesh is no longer shielded from the air, so oxygen is absorbed
at a higher rate, causing faster oxidation, the end result of which is
rapid decomposition.
I enjoyed researching the subject of apple decomposition on your
behalf. Should you feel that any part of my answer requires correction
or elaboration, don't hesitate to inform me through a Clarification
Request so that I have a chance to meet your needs fully before you
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Regards,
leapinglizard |
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