Ripe Bananas Glow Blue Under UV Light
We all know that ripe bananas are yellow. However, under UV light or black light, the yellow bananas are bright blue which was discovered by scientists at the University of Innsbruck (Austria) and Columbia University (New York, USA).
The usual color appearance of bananas is mainly the because of carotenoids. Under normal light, carotenoids ( natural pigments) appear yellow. Under UV light, , ripening bananas appear blue instead. There is no difference between naturally ripened bananas and those ripened with the use of ethylene gas. Green, unripe bananas do not fluoresce. The intensity of the luminescence correlates with the breakdown of the green pigment chlorophyll. As the ripening continues to progress, the blue glow decreases. “Surprisingly, this blue luminescence apparently has been entirely overlooked,” says Kräutler.
Why does the breakdown of chlorophyll occur differently in bananas than in other higher plants, including even banana leaves?
Kräutler gives two different explanations: “In contrast to humans, many of the animals that eat bananas can see light in the UV range. The blue luminescence of the banana fruit could give them a distinct signal that the fruit is ripe.” Or perhaps the chlorophyll degradation products also serve a biological function for the banana. The amazingly stable catabolytes could help to prolong the viability of the ripening fruit.
Light-absorbing chlorophyll is behind the fruit's colorful chemistry. Chlorophyll is critical for bananas to grow and is responsible for the green color of unripe bananas. But once ready to eat that is ripen, the chlorophyll quickly breaks down - leaving the recognizable yellow color of carotenoids in the skin to become dominant.
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