Banana-science project for first grade?

Question

why do banana turn brown in the counter or in the refrigerator

?

Answer 1

not enough sunlight

Answer 2

The long story is that it's a browning reaction caused by the group of enzymes called polyphenol oxidases, which react with chemical compounds called polyphenols to produce the browning.  As the skins mature and the cells start to break down, the polyphenol oxidases come into contact with polyphenols and produce the color.  Cold also disrupts the cells and can allow the enzyme and substrate to react (temps below about 56oF will push most bananas to brown after just a few hours of exposure).  The phenolic reaction products, appear to be useful to the plant because they help inhibit mold growth.

I'm not sure how to get this down to first grade level.  Perhaps something more useful would be to look at this same reaction (browning) on the cut surface of apples or potato-- again, it's polyphenols oxidizing, which is why putting cut potatoes under water slows the oxidation -- as will acids like ascorbic acid (vitamin C).  Because you're dealing with cells that are broken and therefore you can get various treatments to them, you can do some experimenting -- will common household acids like lemon juice, vinegar, vitamin C tablets, cream of tartar work?

Would baking soda or Tums work?  Can wrapping a cut piece of apple loosely in plastic wrap work?  Tightly?  Different brands of wrap???

http://chemistry.about.com/od/demonstrat...

http://en.wikipedia.org/wiki/Browning_(c...