I found that image based on the image (in the link in JLx's post) near the top of that page, which showed that apples have sorbitol in them which converts to fructose, and that the sorbitol also exists in the leaves, and converts into fructose in those too - one assumes they were apple leaves.



Anyhow, if apple leaves have naturally occurring sugar alcohol in them, and apples also have sorbitol, then I expect that all fruits and veggies must have it to some degree, including greens such as spinach. I wasn't able to find any information to confirm that, and the image I posted was the simplest one showing a link between sorbitol and fructose, but it seems that it still requires glucose and sorbitol to start the conversion. The image doesn't really show how this happens, whether any great degree of sorbitol conversion needs an outside source of sorbitol or if it's naturally occurring in large enough quantities in vegetation to be significant.



Someone with a lot more scientific knowledge than I have would need to dig around to figure that out - I was stuck at that point, because I don't know any scientific search terms to go any further with it.