What Is Citric Acid?
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Citric acid is a weak organic acid found naturally in citrus fruits like lemons, limes, and oranges. Its chemical formula is C6H8O7 and it gives citrus its sour taste. Citric acid is one of the most widely used food additives, used as preservative, flavor enhancer, and cleaning agent.
Citric acid is one of the most useful and abundant compounds in chemistry and food science. The same compound that makes lemons taste sour is used in soft drinks, cleaning products, pharmaceuticals, and dozens of industrial processes. It's a key intermediate in the metabolism of nearly every living thing through the citric acid cycle (also called the Krebs cycle). Whether you're eating an orange or cleaning your bathroom, you've probably encountered citric acid today.
What is citric acid made of?
Citric acid has the chemical formula C6H8O7 and a molecular structure containing three carboxylic acid groups (–COOH) attached to a central carbon skeleton. The three acid groups give citric acid its strong sour taste and its ability to chelate (bind) metal ions. The compound was first isolated from lemon juice by Swedish chemist Carl Wilhelm Scheele in 1784. Despite being called an acid, citric acid is a weak acid with pKa values around 3.1, 4.7, and 6.4 for its three carboxylic acid groups, much weaker than strong acids like hydrochloric or sulfuric acid.
Where does citric acid come from?
Naturally, citric acid is found in nearly all citrus fruits, with lemons and limes containing the most (about 5-8% by weight). It also occurs in smaller amounts in many other fruits, vegetables, and animal tissues. Commercially, citric acid is now produced almost entirely through fermentation using the mold Aspergillus niger. The mold is fed sugar (often from corn or sugar cane), which it metabolizes into citric acid in large fermentation tanks. The fermented broth is then filtered and purified to produce crystalline citric acid. Global production exceeds 2 million tons per year.
What is citric acid used for?
Citric acid is one of the most versatile food additives in use. It's used as a preservative, pH adjuster, and flavor enhancer in soft drinks, candies, jams, and many processed foods. It chelates metal ions, which is why it's used in cleaning products to remove rust, scale, and mineral deposits. In personal care products, citric acid balances pH and acts as an antioxidant. Pharmaceuticals use it as an effervescent agent (the fizz in Alka-Seltzer comes from citric acid reacting with sodium bicarbonate). Industrial uses include water treatment, electroplating, and concrete additives.
Is citric acid safe?
Citric acid is generally recognized as safe by the FDA and approved for use in food worldwide. The amounts in food and beverages are well below harmful levels. Some people experience tooth enamel erosion from frequent consumption of acidic drinks containing citric acid, same as with citrus fruits. A small number of people may be sensitive to commercially produced citric acid (the fermentation residues, not the acid itself), though this is rare. Citric acid is biodegradable and safe for the environment.
Citric acid is a weak organic acid found naturally in citrus fruits and produced commercially through mold fermentation. As a food preservative, pH adjuster, and cleaning agent, citric acid is one of the most widely used chemicals in modern food and industry. Generally safe in normal amounts, it's likely to remain a staple of food production and household products for the foreseeable future.
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