Debunking the apple myth
So why do apples darken?
Warning! Only under adult supervision.
- fresh apples;
- lemon juice;
- bowl of water;
- resealable bag;
- potassium thiocyanate solution.
Cut a few apples – after a while, the slices darken. Is this due to a high iron content? If you blend an apple with water, the resulting mixture won’t turn red if potassium thiocyanate is added. To keep apple slices fresh longer, put them in a bowl of water and add some lemon juice. Then put the slices in a resealable bag.
Apple cells contain polyphenols. When an apple is cut, its cells are destroyed, and under the action of enzymes and oxygen, the polyphenols are oxidized. This tints the apple slices brown. The iron content in apples is about 0.0001%, which is insufficient not only to darken the slices, but even to cause apple juice to redden when potassium thiocyanate is added. For comparison, an iron(III) chloride solution instantly turns red with the addition of potassium thiocyanate due to the formation of a new iron compound. Lemon juice contains antioxidants that inhibit the oxidation of the polyphenols. Therefore, if you moisten apple slices even with diluted lemon juice, they will stay fresh longer!
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