Photo one is left to right: White LED, UV LED, UV LED with yellow filter. Courtesy: Wikimedia Commons Xofc. Photo two from Proceedings of the National Academy of Science of the US. This site has a complete description and chemistry of the fluorescent character of the banana here.
We are all familiar with the fact that in the fall, leaves begin to change color from green to sometimes brilliant colors, like the red of swamp maples. But, they can also just become brown and fall to the ground. The process is simply the changing of chlorophyll into smaller molecules as photosynthesis ends the life-cycle for that plant for the year. The act of this cell death is called senescence or growing old. The chlorophyll forms catabolites, (smaller metabolites) releasing some energy in the form of fluorescence, but it is generally short-lived and not readily observed. And, the same process occurs in some fruits, like bananas, pears, and apples. But, it has been found that the banana has some interesting differences.
It has been discovered that bananas have different fluorescent signatures as the fruit ages. When green, there is an abundance of chlorophyll and carotene, with no fluorescence. As the banana ripens and become yellow, it fluoresces with a blue color. In fact, the number of days to ripen can be demonstrated by this fluorescence. But even more interesting is the circular patterns caused by cell death which have a distinct fluorescence at 465 nanometers (UV A). Although I have seen these peculiar cell deaths, I was not able to photograph them.
It is always amazing to me that the natural world around us still contains many secrets and the excitement continues when curiosity causes us to look for new and interesting natural processes…
It has been discovered that bananas have different fluorescent signatures as the fruit ages. When green, there is an abundance of chlorophyll and carotene, with no fluorescence. As the banana ripens and become yellow, it fluoresces with a blue color. In fact, the number of days to ripen can be demonstrated by this fluorescence. But even more interesting is the circular patterns caused by cell death which have a distinct fluorescence at 465 nanometers (UV A). Although I have seen these peculiar cell deaths, I was not able to photograph them.
It is always amazing to me that the natural world around us still contains many secrets and the excitement continues when curiosity causes us to look for new and interesting natural processes…
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