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Citric Acid - Organic Acid CAS 77-92-9

Citric Acid (CAS 77-92-9) - Properties, Applications, and Safety

Citric acid (2-hydroxypropane-1,2,3-tricarboxylic acid) is a weak organic acid with the molecular formula C₆H₈O₇ and a molecular weight of 192.12 g/mol. It is a naturally occurring compound found in citrus fruits and is commercially produced by fermentation of sugars using Aspergillus niger. It exists as a colorless, odorless crystalline solid, typically in an anhydrous form. It is one of the most versatile and widely used organic acids in the food, pharmaceutical, cosmetic, and chemical industries.

Physicochemical Properties

  • Appearance: White crystalline powder

  • Odor: Odorless

  • Melting Point: 153–154°C

  • Boiling Point: 309–310°C

  • Density (anhydrous): Approximately 1.66 g/cm³

  • Solubility in water: High; 590–750 g/L at 20°C

  • Solubility in ethanol: Freely soluble

  • Solubility in ether: Sparingly soluble

Mechanism of Action

Citric acid acts through multiple mechanisms:

  • Acidulant: As a weak organic acid, it provides a sour taste and lowers pH in food and beverage systems.

  • Chelating agent: Citric acid forms stable complexes with metal ions such as calcium, magnesium, iron, and copper. This property enhances the effectiveness of detergents, prevents discoloration and oxidation in foods, and stabilizes formulations.

  • Buffer: The citrate system (citric acid/citrate salts) provides effective buffering capacity across a wide pH range (approximately pH 2.5–6.5).

Applications

Food and Beverage Industry: Citric acid is the most widely used food acidulant. It is used as a flavor enhancer, acidifier, preservative, and antioxidant synergist in beverages, confectionery, jams, and processed foods. It accounts for approximately 51% of total citric acid consumption in beverages. It is also used as a pH adjuster and stabilizer in dairy products and infant formulas.

Household and Industrial Cleaning: Citric acid is a key ingredient in descaling agents, dishwashing detergents, and laundry products. It acts as a builder, sequestering hardness ions (calcium, magnesium) to improve detergent performance and prevent soil redeposition. It is effective for removing limescale, rust, and mineral deposits.

Pharmaceuticals: Citric acid is used as a buffer in oral and topical formulations. It is also employed in effervescent tablets, syrups, and as an excipient in various drug delivery systems.

Cosmetics and Personal Care: It is used as a pH adjuster, chelating agent, and mild exfoliant in skincare products, shampoos, and conditioners.

Other Applications: Citric acid is used in metal cleaning, enhanced oil recovery, and as a precursor for citrate esters and other derivatives.

Safety and Regulatory Status

Citric acid is affirmed as Generally Recognized as Safe (GRAS) by the U.S. Food and Drug Administration (FDA) under 21 CFR 184.1033. It is also approved as a food additive under 21 CFR 172.755 and 173.280. The World Health Organization has long considered it safe for use in food.

Storage and Handling

Citric acid is stable and non-hazardous under normal storage conditions. It is hygroscopic and should be stored in airtight containers in a cool, dry place, away from moisture and strong oxidizers. In concentrated powder form, it may cause mild irritation to skin, eyes, and respiratory tract. Use appropriate personal protective equipment (gloves, safety goggles) when handling large quantities.

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