I just completed this novel, written in 1997 and I believe it takes place during the 2nd season of Voyager. Members of the crew start suffering from scurvy, and they learn it’s because of food they harvested from a planet they stopped at. When it’s cooked it causes a reaction that prevent nutrients from being absorbed into the body. Neelix tells them about a species, called the Kirse, though he gives them an ominous warning about their trading habits. But after a futile search for a class M planet in the area to satisfy their needs and with the crew getting sicker Captain Janeway decides they have no choice.