This Week's Experiment - #294 More Cold Tomatoes
OK, so I underestimated you. I usually try to slip as much science into the
experiments as I can, without causing the "science phobic" folks on the list
to run away in panic. A couple of weeks ago I sent an experiment on
tomatoes in the refrigerator. I focused on the experiment of seeing what
changes took place. Since then, I have heard from MANY of you, asking,
wondering or demanding to know WHY the changes took place. With that in
mind, we will take a closer look. For this week's experiment, you will
need:
an apple
a knife
An apple? Isn't this experiment supposed to be about tomatoes? Don't
worry, we will get there. Lets begin with the apple. First, we need to
carefully slice the apple into several pieces. Immediately, eat one of the
pieces. That is not really part of the experiment, but we don't need all of
the pieces and we don't want them to go to waste. In fact, we only need one
or two pieces, so you can snack on the rest of the apple as we go along.
Once you have the slice of apple, look at it carefully. Notice the color,
texture, smell, and of course the taste. Let the slice of apple sit on the
table for about fifteen minutes and then examine it again. Do you notice
any differences? It has probably browned and the texture may have changed too. Let it sit overnight and you will see quite a big difference.
Why do these changes happen? (This is where we get back to the tomato.)
These quick changes happen because the apple is still alive. Alive? Yes,
alive. The apple is still a living thing. It is breathing, although since
it is not using photosynthesis, it takes in oxygen and gives off carbon
dioxide just as you do. Its cells are carrying out all sorts of chemical
processes. It is still a living thing. This thought may take some time to
get used to. When you buy a steak or hamburger from the grocery, it is not
living. The cells have stopped functioning. The only animals that I can
think of that we eat alive are oysters. (I LOVE oysters!!!) Most of the
fresh fruits and vegetables you buy are still alive and carrying on the
processes of life, up until the point where you either cook them or eat them
raw.
Because they are still alive, they react quickly to changes, especially to
injuries. Cutting the apple causes it to release chemicals called phenol
oxidase enzymes. These enzymes react with oxygen and other chemicals in the
apple and cause the brown color. Chemicals released by the injury also
speed up the process of decay, causing the apple to soften and a change in
texture.
The tomatoes we used in the previous experiment were also alive and they
reacted to the cold of the refrigerator. Imagine if we put you some place
very cold. Your body would react, giving you chill bumps, making you
shiver, etc. As you got colder, more and more things in your body would
change. Putting the tomato into the refrigerator caused changes too. When
it gets cold enough something called "chill injury" happens. The cell
membranes change their structure, becoming more gel-like, giving the tomato
a mealy texture. Oxygen levels are reduced and carbon dioxide levels are
increased. The chemical process of ripening stops completely. All sorts
of enzymes and other chemicals are released. Sugar content changes. So do
the chemicals responsible for the flavor and smell.
Chill injury does not happen at the same temperature with all fruit. It is
common with fruits which are used to warm climates, such as bananas. Other
fruit, such as apples, do very well in the refrigerator without any chill
damage. Even different varieties of tomatoes suffer at different
temperatures. Growers want varieties which will resist chill damage,
letting them cool the tomatoes to slow the ripening process as the produce is
on its way to market.
Now that I have finished my apple snack, I am ready for a bacon, lettuce and
tomato sandwich, so I will sign off for now. Have a good week.
From Robert Krampf's Science Education Company
PO Box 60982
Jacksonville, FL 32236-0982
904-388-6381
krampf@aol.com
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