Foods containing high amounts of citric acid include all citrus fruits, particularly lemons and limes. Other fruits, tomatoes, wine, sourdough bread, cheese, sour candies and soft drinks can also contain significant amounts of citric acid.
Citric acid is often a component in sour flavorings for candy, soft drinks and desserts because of its naturally occurring sour taste. It is also commonly used as a food preservative, emulsifier or additive for vitamin tablets and powders. Citric acid has additional applications as a pH balancer in food coloring and pharmaceuticals. It is sometimes confused with but is distinct from vitamin C.
Citric acid plays an important role in the body's metabolism of protein, fats and carbohydrates into usable energy. It also serves a vital function in bones, determining the size of calcium crystals.
Some people experience the uncommon condition of citric acid intolerance with symptoms similar to food allergies. This reaction is actually a response to the fungus Asperillus niger, which is used in the artificial production of citric acid. This is not the same as a citrus allergy, which is generally a mild reaction to citrus proteins, including symptoms of irritation in and around the mouth area. This allergy is also rare.