How would that be done? Do the food slots have little harvester robots that go to the ship's celery garden to pick that stuff for each plate?
Food dispenser transports celery from ships kitchen, where there is small selection of real foodstuff.
That's my thought. We know that the Enterprise has a galley (in "Charlie X", dialogue indicates that they put meatloaves in the ovens and they turned into real turkeys; and we finally saw the galley in Star Trek VI).
IMO, there are real people preparing the food and it "somehow" gets to the food slots, maybe via short range transporters (or some kind of "wired" transport, to avoid all that beaming of energy/matter streams amidships).