Citric acid is a weak organic acid, and it is a natural preservative and is also used to add an acidic, or sour, taste to foods and soft drinks. It can also be used as an environmentally benign cleaning agent.It exists in greater than trace amounts in a variety of fruits and vegetables, mostly citrus fruits. Lemons and limes have particularly high concentrations of the acid.

In supermarket, we can find these products with citric acid :

Orange juice

Vegetable broth

Source : Yahoo