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Oxidation prevention
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    Lemon juice.
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     1. Cut an apple in two half's.

     2. Squeeze a lemon, saving its juice.

     3. Dive the surface of one apple half's in lemon juice.

     4. Leave the two half's rest during one day.

     5. After one day, you can observe that the surface of the apple not dived in the lemon juice is more oxidized than the other.

     6. In the end of two days, the effect of the apple oxidation prevention becomes more evident. (we can conclude that the acid prevents the oxidation of the surface of the apple)

The oxidation of the apple surface is due to the oxygen present in air. As you have verified in the end of the experiment, the apple without lemon juice was darker. On the other hand, the apple with lemon juice didn't have so much oxidation effects. This fact is due to the presence of ascorbic acid (vitamin C) in the lemon juice. The ascorbic acid reacts with oxygen contained in air, not allowing it to attack the apple. Therefore, when you want to preserve a fruit (apple, pear, banana), you should wet the exposed surface in lemon juice. The lemon juice can be considered as a conservative.

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