Citric acid, whose name in the IUPAC nomenclature is: 2-hydroxy-1,2,3-propantricarboxylic acid and whose brute formula is: C6H8O7 is a tricarboxylic acid, solid, colorless, soluble in water over a wide range of pH.
Citric acid is found in traces in fruit and especially of the genus Citrus. In lemon juice its presence is around 3-4% and in the orange 1%. It is also found in green wood, mushrooms, tobacco, wine and even milk. From citric acid, through the reactions with basic compounds, the corresponding salts are obtained, which are citrates.
The presence of citric acid in nature is remarkable; in addition to vegetables and fruit, the plants that contain the highest concentration of citric acid are citrus fruits and among these lemons and limes that have particularly high concentrations of acid.
It was in 1784, by Carl Wilhelm Scheele, that citric acid from lemon juice was first isolated by crystallization. We must wait until 1890 to have the industrial production with chemical extraction from lemon juice. Later it was discovered that both Penicillium and some Aspergillus niger strains could supervise the transformation of sugary substances into citric acid.
Today citric acid is produced by fermentation on an industrial scale using mushrooms (such as Aspergillus niger) or yeasts in bioreactors with a low pH and low iron concentration environment.
Citric acid is an important intermediate product in the catabolism of carbohydrates, a fundamental metabolic pathway for aerobic living beings, both plants, bacteria and animals, including humans. The related biochemical process is called the Krebs cycle.
Citric acid is considered a nutritional factor. It is not essential, since the organism is able to produce it autonomously, but it nevertheless plays a very important role for biological functions. Its main functions are: Together with vitamin C (ascorbic acid) it favors the absorption of iron; prevents the formation of kidney stones of cystine, xanthine and uric acid; it is an excellent urinary alkalizing agent and can be used to enhance the therapeutic activity of drugs or supplements that require basic urine to best perform their therapeutic action, to promote the excretion of drugs with weak acid characteristics. It also performs a mild bactericidal and anti-arthritic action.
Citric acid has multiple uses and applications:
– has the property of reducing water hardness, and for its anti-scale action is used in eco-sustainable softeners for washing in the washing machine and as a descaler for the pipes;
– in cosmetics it can be used as a pH corrector;
– for its descaling and corrosive capacities it is widely used in cleaning products for professional industrial environments.
– it is used as an aroma and a preservative in food and drinks, especially in soft drinks and candies;
– in the food industry it is used, under the name E330, as acidulant and to correct the pH of basic dyes, as an emulsifier, for example in ice cream, as a substitute for lemon juice or to avoid the precipitation of sugar in caramel; citric acid is also widely used in soft drinks, confectionery products, jellies, jams, beers and, in combination with sodium bicarbonate, in effervescent preparations.
Citric acid is also used in pharmacology as an anticoagulant in the storage of extracted blood and as a preservative in pharmaceutical preparations. Metal citrate salts are used to provide minerals in biologically most available form in many food supplements.
The citric acid, in its pure state, is irritating in contact with the skin and eyes, for which protective clothing should be used when handling. Excessive consumption, in the concentrated state, can affect dental enamel.