Citric Acid is a tricarboxylic acid found in citrus fruits. Citric acid is used as an excipient in pharmaceutical preparations due to its antioxidant properties. It maintains stability of active ingredients and is used as a preservative. It is also used as an acidulant to control pH and acts as an anticoagulant by chelating calcium in blood.

Calcium citrate (E333) is a calcium salt of citric acid, an organic acid naturally found in many citrus fruits.

Sodium citrate is the sodium salt of citric acid (E330), a natural acid found in most fruits. On an industrial scale, it is produced by cultivating a fungus (Aspergillus niger) in a sugary nutrient solution.