Citric Acid

Products

Pure citric acid is available in pharmacies and drugstores as an open product. Specialty retailers can order it from Hänseler AG, for example.

Structure and properties

Citric acid (C6H8O7, Mr = 192.1 g/mol) usually exists as a white, crystalline, and odorless powder and is very soluble in water. In practice, citric acid monohydrate (C6H8O7 – H2O) is used. Citric acid is achiral and has a sour taste. Citric acid is found in many fruits (e.g., orange, grapefruit, pineapple), in vegetables, and in plants, and is found in high concentrations in lemon and lime juice. In the human body, it is an important intermediate in the citrate cycle (Krebs cycle). It is broken down to water and carbon dioxide. Citric acid is usually obtained by fermentation of carbohydrates using atoxic strains of mold and subsequent purification. The salts of citric acid are called citrates. For example, sodium citrate, the trisodium salt of citric acid, is used.

Effects

Citric acid (ATC A09AB04) has acidic, irritant, and preservative properties. The effects are mainly due to the deprotonation of the carboxy groups (pKa1 = 3.14, pKa2 = 4.77, pKa3 = 6.39). Citric acid is a stronger acid than, for example, acetic acid (pKa = 4.76). Furthermore, citric acid also complexes metal ions, which inhibits enzymes and oxidation. In this way, it unfolds antioxidant effects and counteracts the browning of fruits and vegetables.

Fields of application

  • In the food industry, as an acidifier and acidity regulator for beverages (e.g. Fanta, Sprite, Red Bull).
  • As a preservative, for example, in elderflower syrup and other syrups, for jams. Citric acid also untersützt the gelation and has a clarifying effect.
  • In cosmetics.
  • To suppress the browning of fruits and vegetables.
  • As a pharmaceutical excipient, for example, for sherbet powder, for the preparation of a citrate buffer.
  • In hypo- and achlorhydria (acid deficiency in the stomach).
  • In detergents, for example, for descaling.

Dosage

To prepare the elderflower syrup, 20 g of citric acid per liter of water is needed.

Incompatibilities

Citric acid is incompatible with various substances. These include bases such as sodium hydrogen carbonate (gas formation), salts of acids (precipitation), and foods such as milk (flocculation).

Adverse effects

Pure citric acid is irritating to the skin, mucous membranes and respiratory tract and may cause sneezing and coughing. When it comes into contact with the eyes, it causes severe eye irritation. Therefore, the safety data sheet even recommends wearing protective gloves, goggles and a mouth guard when handling. When selling citric acid, customers should always be informed about the irritant effects of the powder. In case of accidental contact, the acid should be rinsed off with water. Beverages and foods acidified with citric acid can attack teeth, lead to demineralization, tooth erosion and tooth decay.

Storage

Citric acid should be stored tightly sealed, dry, away from light and heat, and at room temperature. It has a shelf life of three to four years.