This Week's Experiment - #294 More Cold Tomatoes

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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