Citric acid is natural and just comes from fruits, right? Traditionally, yes, but in modern times it is made from corn, the wonderful tax-subsidized modern staple in America. Corn is cheap, and further cheap through subsidies, and its in almost all our food. (See Food, Inc. movie trailer!). When citric acid is processed from corn, it is very volatile and easily releases free glutamic acid, commonly known as MSG.
Citric acid is added several canned products such as tomato sauce, canned tomatoes, salsa, mushrooms, olives, cake mixes, etc.