Citric acid is an α-hydroxy acid found naturally in citrus fruits. It is an essential part of the Krebs cycle and is required by the body for utilization of carbohydrates, fats, and proteins. Citric acid has many uses in food processing, pharmaceuticals and other industries due to its sour acidic taste and ability to act as a preservative and flavoring agent.

Sources of Citric Acid

Citric acid is primarily produced commercially through fermentation of carbohydrates like molasses and corn syrup by the fungus Aspergillus niger. However, citric acid is naturally occurring in citrus fruits in high concentrations. Most citrus fruits contain around 5-8% of their dry weight as citric acid with lemons and limes containing the highest percentages of around 7-8%. Other sources of citric acid include tangerines, oranges, grapefruits, bergamot oranges and other citrus varieties.

Applications in Food Industry

Food processing is one of the largest applications of citric acid due to its sour taste and preservative properties. Citric Acid is commonly added to soft drinks, candies, jams and jellies, canned foods and frozen desserts to enhance flavor profiles. It works as a preservative by lowering the pH of foods making the environment unsuitable for the growth of microorganisms. Citric acid is also used to add a tart taste to processed foods and beverages. It is widely used in bakeries for adding sourness in cakes, cookies and other baked goods. Citric acid acts as a leavening agent by reacting with baking soda to produce carbon dioxide bubbles.

Pharmaceutical Applications

Citric acid has a number of important uses in the pharmaceutical industry. It is used as an antioxidant and preservative in syrups, elixirs and other liquid medications. Citric acid acts as a synergist to enhance the action of antimicrobial preservatives. It is often formulated with antibiotic and anti-fungal creams as a buffering agent. Citric acid improves palatability and helps dissolve medications into solution faster for better absorption. It is also commonly used in effervescent tablets and powders for its acidity and ability to react with sodium bicarbonate to produce carbon dioxide bubbles.

Home and Personal Care Products

Along with food and pharmaceuticals, citric acid has widespread applications in home care and personal care products due to its acidity and cleaning properties. It is commonly used as a replacement for lemon juice in homemade cleaning solutions for removing stains and grease. Citric acid based products are used for cleaning bathroom surfaces, floors, kitchen areas and other household surfaces. In personal care, citric acid acts as an exfoliating agent in skin scrubs and facial washes. It is also utilized in shampoos and conditioners for its ability to remove mineral deposits from hair. Citric acid balances the pH of cosmetics and bath products giving them extended shelf lives.

Industrial Scale Production

Nearly all citric acid produced globally is manufactured through fungal fermentation using the fungus Aspergillus niger which converts carbohydrate feedstocks into citric acid. Most commercial operations use sugar cane molasses or corn steep liquor as growth media for the organisms. The fermentation process is carried out in stainless steel fermenters for several days under controlled pH, temperature and addition of nutrients. Post-fermentation, impurities are removed from the broth through liquid-liquid extraction and the purified citric acid crystals are isolated. Major producers today are in China, the United States, Germany, Thailand and Brazil with global annual production exceeding 1.5 million tons. New technologies are being developed for more sustainable and cost-effective microbial fermentation methods for citric acid.

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