Citric acid is a white crystalline organic compound with the formula C6H8O7. Citric acid, a strong acid, is used in many fields in industry and daily life. Citric acid is found in almost all plants and in the body fluids of many animals. It is especially found in large quantities in citrus fruits. Citric acid was isolated from the juice of a lemon in England in 1784. The chemical and physical properties of citric acid are as follows:

• Its molecular weight is 210.14 g/mol.
• Its melting point is 153 °C.
• Boiling point is 175 °C.
• Its density is 1.66 g/mL.
• Solubility is high in water and alcohol, low in ether.
• pKa values are -3.1, 4.7 and 6.4.

The production methods of citric acid are as follows:

• Isolation from natural sources: This is the most natural method of citric acid production. Citric acid is obtained by squeezing citric acid-containing fruits such as citrus fruits and evaporating the juice.
• Biochemical synthesis: This is the most common method of citric acid production. Citric acid is produced by fermentation of mold fungi such as Aspergillus niger in sugary solutions. This method also produces carbon dioxide and water.
• Microbial fermentation: This is an alternative method of citric acid production. Yeasts such as Candida albicans produce citric acid using substrates such as glucose or molasses.

Among the uses of citric acid are the following:

• Food industry: Citric acid is one of the most widely used additives in the food industry. Citric acid is used to give foods a sour taste, regulate acidity, use as a color stabilizer, prevent oxidation and extend shelf life. For example, citric acid is used in products such as jams, preserves, confectionery, frozen foods, fruit juices, carbonated drinks and instant teas.
• Pharmaceutical industry: Citric acid is also used in the pharmaceutical industry for various purposes. Citric acid is used to increase the solubility of drugs, to prepare buffer solutions, and as an antacid.
• Cosmetics industry: Citric acid also plays an important role in the cosmetics industry. It is used as a moisturizer, exfoliant and pH adjuster in skin care products. It is also used as a brightener and color protectant in hair care products.
• Cleaning industry Citric acid is also used as an effective agent in the cleaning industry. Citric acid is used to remove rust from metal surfaces, remove lime stains and prevent bad odors.
• Disinfectant industry: Citric acid is a chemical also used in the disinfectant industry. Citric acid is used to kill bacteria and viruses, prevent infections and clean wounds.