Does the antioxidant action of Quercetin work to break down the reactive nitrogen intermediates i.e. free radicals, which normal exhibit antibacterial activity in the gut, thus resulting in reduction in the antimicrobial effect of acidified nitrates on common gut pathogens??

Well Quercetin is an antioxidant so that bit is right. I have never heard of free radicals ehibiting antibacterial action in the gut but just looked it up and there seems to be a lot of journal entires on it- you learn somethig new everyday!

It makes sense to me, I would need to see some studies on it to be convinced that there is a significant effect in vivo.

Strange question, why do you ask?