Why Do Bananas Turn Brown?

Most people are familiar with the different colors that bananas might have depending on where this wonderful fruit is in its life cycle. When bananas grow they form and get bigger inside a thick green skin. People and some animals like bananas when they are perfectly ripe. The signal is the bright yellow color of the peel.

In room temperature, an unripe banana will go from green to yellow over a short period of time. This process will go more quickly with higher temperatures. Bananas placed in a refrigerator will ripen, but more slowly. The peel will get very dark but the banana remains edible.

The next step is, of course, bananas that become over-ripe. The consistent yellow color of the skin will develop dark spots, the fruit inside the peel will get soft and eventually the peel may become completely dark brown. The question is – why does this happen?

According to the scientific explanation, there is an enzyme in bananas called polyphenol oxidase. When this reacts with the oxygen in the air the brown color starts to cover the peel. Keeping bananas sealed and away from oxygen as much as possible may slow this browning process. Of course, eating bananas immediately when they are ripe will do the trick as well!

It’s interesting to note that people have experimented with various ways to keep these fruits from turning brown. One of the simple, inexpensive ways is to sprinkle the fruit with an acidic juice, such as lemon juice. This juice seems to “de-activate” the enzyme. Others have suggested that heating the bananas will do the same thing. A few particular commercial preservatives may be used to keep bananas and other fruit from getting too brown.

The other name for the enzyme culprit is tyrosinase. Some have compared the effects of mixing this enzyme with oxygen to “rust.” In fact, the process and result are quite similar to the rusting of metal that is left in the open to come in contact with oxygen and moisture. The basic materials of the object react to oxygen in the atmosphere and the surface begins to deteriorate.

People have also been creative in keeping bananas, apples and other fruit from turning brown when the fruit is sliced. Of course, slicing exposes more of the delicate inside fruit to oxygen, which hastens the browning process. Partially slicing the fruit and sealing it in a plastic container will certainly slow this down. The truth is, however, that any fruit picked and shipped to be used as food will turn brown and become over-ripe in time. Bananas are no different in this regard.

Written by Lucas Beaumont

Generalist. Wikipedia contributor. Elementary school teacher from Saskatchewan, Canada.

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