nature of sticky substances?

[Till]

I would like to know more about the chemical nature of sticky substances like poncirin etc. Perhaps here is somebody who has scientific background (genetics, chemistry, or just read something) that can help me to get a bit deaper understanding.

I got the question because of some observations:

--> Poncirus contains a sticky substance called poncirin. It is often described as bitter and certainly as disgusting. Yet not all types of poncirus get bitter fruits (bitter in the narrow sence of the word: bitter like vermouth) while all - so far as I know - contain a sticky substance.

--> Some poncirus hybrids that I have tasted (Morton, Swingle 5 Star, African Shadock x Poncirus, a certain Citrumelo probably Sacaton) contain flavour components associated with the sticky substance of poncirus, some however very deluded (Morton). Yet pure poncirus juice often looses its disgusting flavour when it is allowed to stand one night in an open glas so that the sticky substance sinks to the ground. Even the odour of the juice is then pretty good. The same is true for Morton juice which hardly contains any sticky substance. If even the odor of the juice becomes good is then the bad taste perhaps something more volatile than the sticky something?

--> A fruit of Dunstan citrumelo that I could taste definitely contained a sticky substance but I found its taste not disguisting at all. The fruits were a bit sticky but tasted very good. So is the sticky substance really the reason for the bad poncirus taste or is the bad taste something independant of the sticky something? Does the sticky substance only accumulate the bad taste that would be there even if there was not resin in the fruits? Or is the sticky substance in Dunstan Citrumelo something chemically different from that in poncirus fruits?

--> C. ichangensis also contains a sticky substance around its seeds. But it tastes different from that in poncirus and is, at least to my taste, much more tolerable than that of poncirus. Is it chemically different?

--> C. australasiaca has some "glue" around its seeds not much but something. It tastes, however, ok.

--> The peel of pumelos (C. maxima) has a taste remiscent of poncirus fruits. Is it the same substance as in poncirus fruits?


To sume up my questions:
--> How many different sticky substances exist in citrus (including poncirus and eremocitrus)?
--> To what degree shall we distinguish between the sticky substance and disgusting taste?

[Ilya11]

Till,
Repulsive taste of PT fruits is due to the multiple compounds. Actually poncirin has nothing to do with sticky internal oils. It is a bitter flavanoid soluble in water. The overall bitterness of PT fruits is due mostly to it and  another flavanoid - naringin and limonoid derivatives. Poncirin is also present in other citrus fruits like grapefruits, ougan mandarines, etc. 
Oils in the vesicles are sesquiterpene hydrocarbones. There is also  a presence  of sulfur containing volatile compounds adding to the overall unpleasant smell and taste.

link

[Till]

Thank you, Ilya.

Am I right that naringin is also reponsible for the bitter taste of old Navel orange juice? If so it would be interesting that the juice of some (all?) poncirus fruits does not became more bitter with age. Morton juice also does not became more bitter with age.

[Ilya11]

No,  navel oranges contain limonin glucosides  that are not bitter by itself, but upon the juice  storage or heating  are giving a bitter free limonin compound.

[Till]

Ah, thank you.

[pagnr]

Citrus garrawayi, the Mount White Lime from Cape York has a very sticky pulp component.
It will really stick to your teeth, and is hard to get off, more so if you eat a few fruit at once.

[Till]

Interesting.  Sticky substances are quite common in Microcitrus, aren't they?