Questions About Fluorescent Compounds in Overripe Bananas and Chlorophyll

Hi everyone,

I previously asked this question in the biochemistry thread but didn’t receive any answers, so I’m reposting it here in the general chemistry thread.

Many of you might know that as bananas overripen, dark spots develop on their skins. Around these spots, a narrow ring of chemical compounds forms, which exhibit fluorescent properties.

I have a couple of questions regarding this phenomenon:

Could these fluorescent compounds be stabilized and stored for future use?
Based on my research, these compounds appear to form as chlorophyll decomposes. If one were to extract chlorophyll from green leaves, would they observe a similar fluorescence effect? Additionally, would the compound be stable enough to store?
Looking forward to your insights!

-Sarinox

It's hard to say much about stability without knowing what the compound is. If it's an intermediate of the process that forms the spots, and the spots don't fluoresce, it seems like it doesn't survive very long in musa. If you want to accumulate enough raw material to have any hope of extracting a useful quantity (vs. just buying a truckload of bananas all at once) you'll need to find some way to inhibit that reaction because the browning process happily proceeds in a domestic freezer. Maybe try soaking in ascorbic acid before freezing? Honestly, this seems like a big pain

Chlorophyll is fluorescent, and you can see a photo of an extract fluorescing on that page. But I'd expect it to be red, not blue as in your photo. As far as stability goes, it's (unsurprisingly) light-sensitive and not known for being especially stable generally, but this paper reports that it can be fairly stable if if purified, crystallized, and stored in the dark.

Quote: Originally posted by Rainwater

You can try a tlc plate to seperate the compounds. And maybe identifying a few based on polarity

Quote: Originally posted by drakedevel

Oh, interesting! That first paper makes it clear that the entire skin is fluorescent, not just the rings. I thought that looked like the case from sarinox's pictures, but the post only mentioned the rings, so I figured it must have just been an artifact of the camera w/ UV light. If the whole skin is fluorescent that sure seems more practical to extract, at least. (Though the second paper looks a bit pessimistic on the prospects of that...)

Quote: Originally posted by sarinox

Hi Drakedevel, I suggest you try shining a UV light on a banana! The photo in the paper looks and feels different from what I observed. I used a UV light machine designed for verifying currency authenticity, but what I saw didn’t exactly match the images in the paper. Maybe the wavelength of my UV light is slightly different, or perhaps my eyes aren’t as sensitive to perceiving the fluorescence—I’m not sure!

Quote: Originally posted by drakedevel

I definitely will the next time I get groceries! I have a 365nm LED flashlight that I use surpisingly often, so often that I'm actually a bit surprised I've never tried it on a banana before. Makes optical brighteners shine blue so brightly you'd think it was a blue flashlight until you point it at something non-fluorescent.