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