sour salt

Calcium citrate
IUPAC name	2-hydroxy-1,2,3-propane- tricarboxylic acid calcium salt (2:3)
Other names	E333
Identifiers
CAS number	813-94-5,5785-44-4 (tetrahydrate)
EC number	212-391-7
SMILES	C(C(=O)[O-])C(CC(=O)[O-])(C(=O)[O-])O. C(C(=O)[O-])C(CC(=O)[O-])(C(=O)[O-])O. [Ca+2].[Ca+2].[Ca+2]
Properties
Molecular formula	Ca3(C6H5O7)2
Molar mass	498.46 g/mol (anhydrous) 570.5 g/mol (tetrahydrate)
Appearance	White powder
Density	1.63 g/cm3, solid
Melting point	120 °C (loses water)
Boiling point	Decomposes
Solubility in water	0.085 g/100 mL (18°C) 0.095 g/100 mL (25 °C)
Hazards
MSDS	External MSDS
Main hazards	Irritant
Related compounds
Other cations	Sodium citrate
Except where noted otherwise, data are given for materials in their standard state (at 25 °C, 100 kPa)
Infobox references

Calcium citrate is the calcium salt of citric acid. It is commonly used as a food additive (E333), usually as a preservative, but sometimes for flavor. In this sense, it is similar to sodium citrate. Calcium citrate is also used as a water softener because the citrate ions can chelate unwanted metal ions. Calcium citrate is also found in some dietary calcium supplements (e.g. Citracal). Calcium makes up 21% of calcium citrate by weight.

Chemical properties

Like citric acid, calcium citrate has a sour taste. Like other salts, however, it also has a salty taste. For this reason, citrates such as sodium and calcium citrate are commonly known as sour salt.

Production

Calcium citrate is an intermediate in the isolation of citric acid from the fermentation process by which citric acid is produced industrially.^[1] The citric acid in the broth solution is neutralized by calcium hydroxide, precipitating insoluble calcium citrate. This is then filtered off from the rest of the broth and washed to give clean calcium citrate.

The calcium citrate thus produced may be sold as-is, or it may be converted to citric acid using dilute sulfuric acid.

Biological role

Bioavailability of calcium is debated, found to be equal to that of the cheaper calcium carbonate,^[2] or up to 2.5 times higher. Due to the possibility of higher absorption, patients who have undergone the Roux-en-Y variety of weight-loss surgery (also known as gastric bypass) are usually instructed to take calcium citrate as a dietary supplement.

References