I noticed after I cut a piece of stem from a colocasia, as expected - water came seeping slowly out. But after a few minutes it'd start to become brown (the actual liquid, not just the surface). Eventually (maybe 20min) it'll dry and become blackish brown. The question I have is, what makes it brown, is it oxidation of some sugars or some protective phytochromes being oxidized from the sunlight? I'm into plant chem, so I was wondering. Thanks. Pics are taken in order - right after cutting, 3min, and 20min.