I have had this experience several times in my life. As I recall, it was usually on fish or fresh fruits and vegetables. My mom always told me that some restaurants and retail stores use a chemical preservative that they spray on food to extend it's shelf life. It is a really distinctive and disgusting taste. When I have had this happen in a restaurant, I complain and of course reject the dish. I am unable to eat anything else because I am so turned off. Does anyone in the food/restaurant business know what I am talking about? Does such a thing really happen? I have wondered about this for some time.