A mysterious rash of food poisonings has the city on edge

There was something rotten about this city, and I didn't mean the blue cheese factory. It was the restaurants that went bad, serving bad food made by even worse chefs. My job was to solve the case of the poisonings for the benefit of my unknown (but wealthy) benefactor. The city needed to eat. Were people expected to cook for themselves?

Move food items on your plate to hurt or heal whoever eats it

I would visit each chef, let them serve me terrible food, and rotate the food pieces to fit my plate. The restaurants all serve deadly food, sure, but some foods are healing. As the only (and therefore the best) detective in the city, I had to stop the chefs, one way or another. Placing foods next to each other would strengthen or weaken the poison, maybe even heal whoever eats it. Sorry, mother dear, but I would have to play with my food.

Trick chefs into eating their own food, or convince them to quit

A bit of light conversation with the chefs wouldn't hurt. My plan was to have a nice dialog with each chef in between food servings. After a talk, they might try some of their own food from my plate (if I chose the best dialog option). If they ate enough of their own bad food (health down to zero), they would be out for the count, assuming I was still on my feet. Or maybe there was another way to solve the case, by talking to them. If I could convince them to give up cooking, no one had to die.

Close the restaurants, save the city, get some vacation time in 

I would close the restaurants down, one by one, until there were none left. Then the city would finally be safe from the outbreak of food poisonings, and little old ladies could have their tea time again without a trip to the morgue. It was a long shot, but so far, I had tried nothing and was out of ideas. I might as well sit down at the taster's table and get this show started.