UV

[Max Nihil]

As many of you likely know Capsaicin oils in Capsicum berries are fluorescent under UV.

While the effect is not particularly strong it is of some use in screening and selecting Capsicum fruit for high secreted oil content.

I used an LED type blacklight UV fixture for the photographs.

In the pictures you will see an almost turquoise blue color to the oil, this is from the phone setting and to the eye the oils glow a faint reddish color, which contrasts with the darker tissue colors.

Although LED UV fixtures are far less than ideal it is possible that a more ideal wide spectrum UV light source might be useful in rapidly screening capsicum fruit for high oil content. ✩

The examples photos are from a berry of an elongated orange habanero that was obtained by planting seeds from a few grocery store orange habaneros that were unusually large and long. These seeds produced a wide range of lantern like, mini bell like, and finger like elongated fruits of crisp orange habanero.

I suspect the specimens in the grocery store were either a commercial F1 production hybrid or just a rapid worker based selection of a cultivated population.

I found one plant that produced a high yield of finger like berries that are atypical for an orange hab and I have been examining the berries.
In the second photo you can see inside the berry and observe that near the calyx are spots of glowing oils, these are produced on veins of placental tissue embedded in the inner layer of the upper parts of the berry.

✩Direct visualization of capsaicin and vanillylamine in Capsicum...
SUZUKI et al.

 

[PepperDoc]

Are you certain you are observing fluorescence?

The authors of that paper exited capsaicinoids with a 4th harmonic NdYAG laser at 266 nm, which is invisible (and highly dangerous--if your UV source goes down that far, it is hazardous to expose yourself to it). Then they detected fluorescent emission at 310 nm, which is outside the generally accepted range of human eyesight.

generally speaking, it requires a delocalized pi system of not less than 7 bonds to provide significant fluorescence, especially if detected visually. Capsaicinoids only have a 3 bond system. This is confimed in the emmision spectrum in the paper. At 380 nm, where humans van start to see violet light, there is very very little fluorescent emission.

 

[ahayastani]

Direct visualization of capsaicin and vanillylamine in Capsicum fruit with laser flurometric imaging
 
H. Suzuki e.a.
 
[ CLICK HERE FOR PDF ]
 
Capsaicin. the pungent secondary metabolite found in fruit of the genus Capsicum, and vanillylamine. a metabolic precursor to capsaicin. are used in the food science. pharmaceutical. medical. and forensic industries; however. a rapid method to evaluate fruit for the presence of these two compounds is lacking. The present research describes the in situ visualization of capsaicin and its precursor in Capsicum fruit by laser-induced fluorescence imaging and spectrometry. When excited by ultraviolet lasers at 266 nm. capsaicin and vanillylamine have peak fluorescence emissions at 310 nm. The fluorescence spectra of precursors of capsaicin and analogs, i.e., trans-caffeic acid, trans ferulic acid, trans-para-coumaric acid, vanillyl alcohol. vanillin, vanillic acid, had different peaks than those of capsaicin and vanillylamine. The localization of capsaicin and its immediate precursor. vanillylamine, was imaged with an ultraviolet-sensitive camera after excitation with a laser at 266 nm. Fluorescence images detected at 310 nm showed the localization of capsaicinoid and/ or vanillylamine on the surface of placenta and septa of Capsicum fruits. No fluorescence specific to capsaicin and vanillylamine was observed in seeds or pericarp. Both bell pepper and sweet pepper also showed 310 nm fluorescence on the placental surface, suggesting the accumulation of vanillylamine in the placenta. Laser-induced imaging shows considerable promise as a suitable technique for rapidly screening Capsicum fruit for their capsaicin and vanillylamine contents.
 
 
Note the last phrase of Results & Discussion: Hopefully, a compact device that enables breeders and producers to monitor capsaicin content on site will be developed as a commercial product in the near future. Publication is from 2011.

 

[Demented]

 

[Max Nihil]

I have zero doubt I am observing fluorescence of capsaicin containing oils in the plant.

However I do not suspect that I am observing capsaicin fluorescence directly.

The photographic evidence is direct proof of the technique working and if you try it yourself with a decent UV source you will also see that it works.

It does not work to indicate oils present in vesicles.

If you look at the excitation and emission spectra of capsaicin you will see that despite the narrow excitation spectrum the emission spectrum is broad but faint and goes into the IR spectrum and includes some visible reds.

 

[Max Nihil]

I cut open another fresh habanero from the same plant.

In the above photo the capsaicin containing oils are the yellowish droplets on the placenta and on the vein of placenta like tissue.

In the photo above I used an arrow to indicate a droplet of capsaicin containing oil that is directly on a placenta tissue like vein that is common to this line of orange habanero. This droplet is visible in all photos that follow.

In the two photos above I held the specimen next to a cheap compact fluorescent blacklight bulb. It produces a lot of visible light that doesn't provide as much contrast as other UV sources. The capsaicin containing oils are a more vivid and brighter yellow than the flesh.

In the two photos above I placed the specimen very close to the light and tried to get an angle that shows the faint glow it has that can be seen by the naked eye. The glow is a faint pinkish/orangeish/reddish glow that although is not very bright it is still bright enough to be seen with ease in person.

The greater the quantity of the oil the brighter the color and contrast and it is immediately obvious which specimens contain more oils when they are compared side by side under the light.

I suspect certain colors of glasses would enhance the contrast and be useful in shielding the viewer's eyes from the UV light.

UV light is dangerous and doing anything that involves prolonged eye and skin is incredibly stupid... even with novelty blacklight sources.

 

[ahayastani]

I do not doubt you see something, but the question is whether it is or isn't capsaicin (or capsainoids) what you see. The oil droplets will contain a plethora of structurally different compounds (phenolic antioxidants for instance) that could "light up" with UV.

 

[Max Nihil]

I do not doubt you see something, but the question is whether it is or isn't capsaicin (or capsainoids) what you see. The oil droplets will contain a plethora of structurally different compounds (phenolic antioxidants for instance) that could "light up" with UV.

You aren't wrong.

However I do suggest people try it for themselves and compare different varieties of Capsicum with a range of SHU values and present photographic evidence that contradicts or confirms my results in terms of hotter types with more oils being visually brighter.