Just a guess from a p-chemist who vaguely remembers that organic stuff. If
there is any chemistry that distinguishes fruity flavor, it is probably
associated with simple esters (organic acid + alcohol gives ester linkage
with elimination of a water molecule). I don't have a list handy, but many
simple esters like ethyl butrate have fruity odors. Maybe you would find
that the vegetably things lack esters, maybe because the plant doesn't pack
these tissues with "eat me" chemicals.
Rick