08 Oct STEM Challenge – Why do Apples Turn Brown?
Why do apples turn brown and what can you do about it? Do all apple slices turn brown at the same rate or is there something we can do to keep them fresh for longer? Let’s try to answer these burning apple science questions with an apple oxidation experiment!
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- 2 apples (You will need these to be in slices, but it is a great practical life activity to let your child safely slice the apples themselves!)
- Lemon Juice or a real lemon
- Airtight Tupperware container
- Rubber band
- Paper Plates
For this experiment, we will be testing four theories on how to keep apple slices from browning. Each number should have it’s own plate, make sure to label them! Make a prediction: Which apple slices will start to brown first? Which second? Which third? And Which last?
- Place a slice of apple with nothing done to them on a plate
- Place a slice of apple that is sprinkled in lemon juice.
- Place a slice of apple in an airtight container.
- Slice an entire apple and “put it back together” with a rubber band
Now start your timer and see what happens! Make a note of how quickly each apple slice starts to brown. Two of them should start to brown after 5 minutes or so. The next will be about 20 minutes and the last will last a few hours!
As you may have seen and maybe even guessed, the slices with the lemon juice last the longest. So, why does the lemon juice work? It has to do with a chemical reaction called oxidation. The ascorbic acid (vitamin C) in the lemon juice creates a barrier between the apple slice and oxygen in the air. Without the acid, the enzymes in the exposed apple slices would react with oxygen (oxidation) and start turning the apple brown. The lemon juice barrier protects the apple enzymes.