Scene Context: The crew complains about paste-like food, Turbo dreams of the crunch of a real apple, and Les is glad that, due to swollen mucous membranes, he can barely smell the dirty ship.
Essence of the Phenomenon: Due to the absence of hydrostatic pressure, bodily fluids shift to the head, causing persistent nasopharyngeal congestion. Astronauts are effectively in a state of a permanent "space cold," which radically suppresses their sense of smell and, consequently, taste.
Scientific Basis: Since olfaction accounts for up to 80% of flavor perception, standard food in orbit seems bland, "cardboard-like," and tasteless to astronauts. That is why space menus traditionally feature excessive amounts of hot sauces, salt, and spices (e.g., sriracha or wasabi). Turbo's desire to eat a solid apple illustrates the psychological phenomenon of "texture starvation." Space food is predominantly freeze-dried, moist, or paste-like to prevent the formation of crumbs (which in microgravity could get into eyes or short-circuit electronics). The lack of crunchy food severely impacts crew morale during long-duration missions.
Current Limitations: The physiology of fluid shifts cannot be tricked by any medication without harming the astronaut's health. Until engineering can provide ships with a full centrifuge to create artificial gravity, crews will always suffer from congestion, diminished taste, and loss of smell.