I can't see that it's a complication of UC.....there are a variety of reasons one would have bad breath, however.
Medications can definitely cause dryness in the mouth. Stress, foods, lack of water, smoking, spices, and poor dental hygiene, sinus infection/problems, lung infections, etc can cause it too. Even reflux might be a cause as well as an imbalance of bacteria in the mouth. Many mouth rinses can cause worse bad breath than not using it.
I would say most people would have bad breath after a meal if the mouth isn't freshened by brushing the teeth and tongue. Regular flossing is also a huge plus.
You should, however, get it checked out by a doctor to find the cause and hopefully it can be helped.