Citric acid is a weak organic acid, and is triprotic. It is anatural preservative and is also used to add an acidic, or sour,taste to foods and soft drinks. In biochemistry, it is important asan intermediate in the citric acid cycle and therefore occurs inthe metabolism of almost all living things. It also serves as anenvironmentally benign cleaning agent and acts as anantioxidant.

Citric acid exists in a variety of fruits and vegetables, mostnotably citrus fruits. Lemons and limes have particularly highconcentrations of the acid; It can constitute as much as 8% of thedry weight of these fruits (1.44 and 1.38 grams per ounce of thejuices, respectively[1]). The concentrations of citric acid incitrus fruits range from. 005 mol/L for oranges and grapefruits to.030 mol/L in lemons and limes. These values will vary depending onthe circumstances in which the fruit was grown.