When you cut an apple, you must have seen the apple slices turn brown soon.
When you peel a potato, a black-brown color develops on it after a while.
What causes this change in color and can you stop it? The answer lies in chemistry.
When you cut or peel an apple, its cells are damaged and exposed to the air.
Oxygen from the air fastens a simple chemical reaction inside the cells of the apple. In this reaction, an enzyme called polyphenol oxidase converts chemicals called phenols into melanin. As a result, the apple turns brown. Melanin is the same pigment that gives color to our skin, hair and the irises of our eyes.
Cold temperature as well as acidic conditions can effectively weaken the action of polyphenol oxidase. Hence, refrigeration or application of lemon juice or vinegar helps to slow down the chemical reaction and the resulting browning.
The enzymatic browning occurs not only when you cut the apple, but also if the apple gets damaged or when it gets old.
In addition to apples and potatoes, the same discoloration is seen in many other fruits and vegetables including avocados, pears, peaches, bananas, brinjals/eggplants as well as in mushrooms.
The next time you cut an apple, apply some lemon juice to a small slice and check if it goes as brown as the other slices. Does the experiment work?
Sources and further reading:
Fruits Gone Bad? Discover Enzymatic Browning (https://www.scientificamerican.com/article/fruits-gone-bad-discover-enzymatic-browning/)
Food investigation: conducting experiments II (https://www.ifst.org/lovefoodlovescience/resources/food-investigation-conducting-experiments-ii)
Enzymatic browning (http://www.food-info.net/uk/colour/enzymaticbrowning.htm)
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