Thursday, September 19, 2013

Apple Science

In this week's book, Sierra got in big trouble when she brought her mom's lunch bag by mistake because there was a knife in it. The knife was probably there so Sierra's mom could cut her apple right before she ate it so it wouldn't go brown. Do you agree? Let's see if we can come up with another way that Sierra's mom could keep her apple fresh!

Materials:
  • apple slices
  • lemon or lime juice (sugar water works too, but for different reasons)
  • plastic wrap
  • fridge and freezer

Cut the apple into slices and decide what you're going to do with each one. We kept one just on the counter (as the control in our experiment.) We put one in the fridge, one in the freezer, and one outside. Then we wrapped one in plastic wrap and coated another in lime juice. The rest of the apple slices were part of our taste test program--and they tasted great. :)

Then all we had to do was wait and observe! We took pictures of our apples after 24 hours:

And after 48 hours:

After two days, the only one that still looked edible was the frozen apple slice. (The plastic wrap one was close.) It didn't take days to see a difference, though--we definitely started to notice changes in our apples after just a couple of hours! But why? What was happening?

Cutting the apple actually damages the cells on the surfaces where you slice it. That damages the cells on the surface and exposes some of the enzymes, and these enzymes react with the oxygen in the air. These reactions slow down in cold temperatures like in the fridge or especially the freezer. And they should slow down when there's lemon juice on the surface because it has antioxidants (chemicals like citric acid and ascorbic acid that slow down oxidation reactions like the ones happening on the apple.) Plastic wrap keeps most of the oxygen away from the apple too. (Check out this article for more information, or visit this site.)

You can try your own ideas for keeping apples fresh too, or try the experiment with other fruits or vegetables. Have fun!

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