E332 (Potassium citrate)  is a chemical compound, inorganic salt of citric acid (α and β-hydroxytricarboxylic acid).

The name 'potassium citrate' can be broken down as follows:

• Potassium refers to the potassium ions (K+) present in the compound. Potassium is an essential mineral for heart function and plays a key role in skeletal and smooth muscle contraction, making it important for normal digestive and muscle function.
• Citrate refers to the citrate ion (C₆H₅O₇^3-), which is a derivative of citric acid. Citric acid is a weak organic acid that occurs naturally in citrus fruits.

Potassium citrate synthesis can be achieved by neutralising citric acid with potassium hydroxide in different steps:

• Neutralisation. Citric acid is combined with potassium hydroxide. Citric acid reacts with potassium hydroxide to form potassium citrate and water. The chemical equation for this reaction is: 3 KOH + C6H8O7 → K3C6H5O7 + 3 H2O
• Crystallisation. The resulting solution is then cooled, which causes the potassium citrate to crystallise.
• Filtration and drying. The crystals are then filtered from the solution and dried to obtain pure potassium citrate.

The industrial production of citric acid takes place by mycological fermentation of raw sugar from Aspergillus niger and subsequent crystallisation with alkaline solutions.

It appears as an odourless white crystalline powder with a slightly saline taste. Slightly hygroscopic, easily soluble in water, slow to dissolve in glycerine, insoluble in alcohol and ethanol.

What it is used for and where

Medical

In addition to its main function as a preservative, Potassium Citrate is also a decent antimicrobial, although inferior to Potassium Acetate (1). Potassium citrate is used to improve bone mineral density and to prevent metabolic acidosis in kidney disease (2) and has enhanced the beneficial effects of calcium and vitamin D in osteopenic women with a documented potassium and citrate deficiency and a metabolic profile compatible with low-grade acidosis (3). It has been shown that potassium citrate can increase urine pH values and dissolve kidney stones (4) and that alkaline therapy increases bone mineral density and corrects abnormal bone cell function. 

Some improvement has been achieved in the treatment of dehydration by potassium citrate supplementation.

It has been observed that potassium citrate, with its alkanising action, can alleviate the discomfort of cystitis caused by lower urinary tract infections (5).

Indicated in the treatment of potassium deficiency.

Studies have shown its efficacy in strengthening bones and thus being less prone to fractures and osteoporosis.

Dentistry

The inclusion of potassium citrate in toothpastes reduced tooth sensitivity after 3 weeks (6) and has an antibacterial function.

Food

It is labelled E332 on the European food additives list as an acidity regulator, but also has antiseptic properties. Emulsifier in cheese.

Cosmetics

Chelating and buffering agent in cosmetic products with preservative properties.

• Buffering agent. Iingredient that can bring an alkaline or acid solution to a certain pH level and prevent it from changing, in practice a pH stabiliser that can effectively resist instability and pH change.
• Chelating agent. It has the function of preventing unstable reactions and improving the bioavailability of chemical components within a product, and removes calcium and magnesium cations that can cause cloudiness in clear liquids.

"Potassium citrate studies"

Typical commercial product characteristics Potassium Citrate

• Molecular Formula     K₃C₆H₅O₇     C₆H₅K₃O₇      C₆H₅O₇K₃·H₂O
• Linear Formula  HOC(COOK)(CH₂COOK)₂ · H₂O
• Molecular Weight    306.394 g/mol
• Exact Mass     305.894653
• CAS    866-84-2  7778-49-6
• EC Number    212-755-5     612-062-1
• UNII    86R1NVR0HW
• DSSTox Substance ID  DTXSID8027325     DTXSID0041222
• IUPAC  tripotassium;2-hydroxypropane-1,2,3-tricarboxylate
• InChl=1S/C6H8O7.3K/c7-3(8)1-6(13,5(11)12)2-4(9)10;;;/h13H,1-2H2,(H,7,8)(H,9,10)(H,11,12);;;/q;3*+1/p-3
• InChl Key      QEEAPRPFLLJWCF-UHFFFAOYSA-K
• SMILES   C(C(=O)[O-])C(CC(=O)[O-])(C(=O)[O-])O.[K+].[K+].[K+]
• MDL number  MFCD00150442
• PubChem Substance ID    329750903
• ChEBI  64733
• NCI    C29372
• RXCUI    1374802
• Beilstein     3924344
• HS Code     2918150000

Synonyms: 

• Tripotassium citrate
• Potassium citrate anhydrous
• Citric acid, tripotassium salt
• 1,2,3-Propanetricarboxylic acid, 2-hydroxy-, tripotassium salt
• Potassium tribasic citrate

References________________________________________________________________________

(1) Liato V, Labrie S, Aïder M. Electro-activation of potassium acetate, potassium citrate and calcium lactate: impact on solution acidity, Redox potential, vibrational properties of Raman spectra and antibacterial activity on E. coli O157:H7 at ambient temperature. Springerplus. 2016 Oct 10;5(1):1760. doi: 10.1186/s40064-016-3453-1. 

(2) Domrongkitchaiporn S, Pongskul C, Sirikulchayanonta V, Stitchantrakul W, Leeprasert V, Ongphiphadhanakul B, Radinahamed P, Rajatanavin R. Bone histology and bone mineral density after correction of acidosis in distal renal tubular acidosis. Kidney Int. 2002 Dec;62(6):2160-6. doi: 10.1046/j.1523-1755.2002.00656.x.

(3) Granchi D, Caudarella R, Ripamonti C, Spinnato P, Bazzocchi A, Massa A, Baldini N. Potassium Citrate Supplementation Decreases the Biochemical Markers of Bone Loss in a Group of Osteopenic Women: The Results of a Randomized, Double-Blind, Placebo-Controlled Pilot Study. Nutrients. 2018 Sep 12;10(9):1293. doi: 10.3390/nu10091293. 

(4) Barbera M, Tsirgiotis A, Barbera M, Paola Q. The importance of potassium citrate and potassium bicarbonate in the treatment of uric acid renal stones. Arch Ital Urol Androl. 2016 Dec 30;88(4):341-342. doi: 10.4081/aiua.2016.4.341.

(5) Elizabeth JE, Carter NJ. Potassium citrate mixture: soothing but not harmless? Br Med J (Clin Res Ed). 1987 Oct 17;295(6604):993. doi: 10.1136/bmj.295.6604.993.

(6) Chesters R, Kaufman HW, Wolff MS, Huntington E, Kleinberg I. Use of multiple sensitivity measurements and logit statistical analysis to assess the effectiveness of a potassium-citrate-containing dentifrice in reducing dentinal hypersensitivity. J Clin Periodontol. 1992 Apr;19(4):256-61. doi: 10.1111/j.1600-051x.1992.tb00463.x.