I used to purchase a deli potato salad that had a very distinctive taste to it. This was at a Wawa in Philadelphia in 1982. I found a similar (if not the same) potato salad in the Harrisburg area in 1997. Both places no longer carry this particular potato salad. At the second place it was labeled their 'Classic' potato salad.
Anyway, in addition to the taste of mayo and some mustard, vinegar and some sweetness there was a flavor that had a bit of a tang and a bit of a burn. Not hot (piquant) but almost a tingle. This is hard to describe.
When trying to replicate it (I've tried a lot of things...) the thing that came closest was probably juice from a jar of pickled banana pepper rings, but it still was not it.
I'm thinking it might have been sodium benzoate? or another preservative? or monosodium glutemate? It did enhance my flavor experience of the potato salad (umami). And as much as I crave that taste, my wife has an equally strong aversion to it.