If the active development agent in whatever developer you are about to brew is some dihydroxy-benzene, then sulfite may act as scavenger for oxidized developer, and thereby make development more even (c.f. Hydroquinone based developers with or without sulfite).
While e.g. oxidized Catechol or Pyrogallol form brown insoluble compounds at low sulfite levels (c.f. staining developers), this may not work as well with these substituted Catechols, so sulfite may be good for these, too.
If the most active development agent in your pineapple juice is Ascorbic Acid, then sulfite won't scavenge oxidized Ascorbate, but it will still do all these things which PhotoEngineer brought up.
PS: One more thing that I would like to bring up: both, dihydroxy benzenes and Ascorbic Acid will need moderately high pH of about 10 in order to develop film, and none of these developers will be remotely edible. Since coffee appears to contain a compound which accelerates development by ascorbate, it might be possible to use Sodium Bicarbonate instead of Sodium Carbonate as alkali, plus one could leave out the sulfite. This could potentially create a developer, which would actually be edible, although not necessarily tasty.