An experiment to demonstrate thatlemon juice keeps slices of apple fresh |
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Principle |
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Almost all plants contain polyphenol oxidase, and it is believed that plants use this enzyme as part of their defense mechanism.
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When a plant is damaged, the browning of the affected area is thought to discourage animals and insects from eating the plant any further.
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It also might help the plant heal because the browning creates an antibacterial effect, preventing germs from destroying the plant even more.
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Lemon juice helps to keep the apple from browning, because it contains ascorbic acid (Vitamin C) and it has a low (acidic) pH level.
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Ascorbic acid reacts with oxygen before it reacts with the polyphenol oxidase.
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However, once the ascorbic acid gets used up, the oxygen will start reacting with the enzyme and browning will occur.
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Lemon juice's low pH level also helps prevent browning.
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Materials Required |
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- An apple
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- Sharp knife
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- Lemon juice
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- Clock
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Procedure |
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Cut the apple in half from top to bottom.
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On one apple half, lightly coat the white part of the apple with lemon juice.
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Leave the other half uncoated.
(The uncoated half is your "control" sample and lets you see what normally happens to a cut open apple)
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Observe the colour of both the apple halves, then place them white-part-up on a counter or tabletop.
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Observe the apples again after 30 minutes. Notice any colour change and/or difference in appearance.
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Look at the apples again periodically throughout the day. What do you find?
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Observation |
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When an apple is cut open, an enzyme called polyphenol oxidase is released from the cells of the apple and reacts with the oxygen in the air.
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This reaction causes the fruit to turn brown, similar to rust forming on metal.
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