Wouldn't "pepperet' be correct because "pepperen" is the the pepper plant. According to my Norwegian teacher the phrase "saltet og pepperet" is the correct one unless you mean the pepper plant.
Sitron and Sitronen sound the same or at least nearly the same. It's very difficult to distinguish :( I only made an assumption since there was saltet og pepperen with it. I guess it all comes with practice