was there any food that he just couldn't eat

IIRC he could barely stomach the special stinky tofu in the Taiwan episode (the usual stuff that was sold by the street vendors he was okay with, but then he paid a visit to a lady who makes a real "special" stinky tofu that I guess was just too much for Zimmern).

Also, again IIRC, when he was in Morocco, he went out in the countryside and went to some place that had this dish that comprised putrified meats, fats, and maybe eggs? Anyway, he could barely get one bite down. I thought he was gonna' puke. It looked and sounded disgusting, the way he described how they made it...

Another food that he barely got down was some sort of deep-fried fish egg sac, I think it was from some sort of lake fish in his Minnesota episode. On a scale of one to ten, he gave it a negative one for being so unappetizing.

There's also been a few other foods that he could barely swallow, can't remember all of them, but yes, he has in fact been bested by several disgusting food items.

he doesn't like spam...and I've seen him in a north African or Asian port episode where there were rotting shellfish and he basically said that his system didn't have the right bacteria and he would get very ill if he at it.

But he'll eat everything on most shows and typically wont eat something because its something he's had before and hates the texture or if it something local and rotting and will make him sick.