Calcium lactate

Calcium lactate is a white crystalline salt with formula C6H10CaO6, consisting of two lactate anions H3C(CHOH)CO2− for each calcium cation Ca2+. It forms several hydrates, the most common being the pentahydrate C6H10CaO6·5H2O. Calcium lactate is used in medicine, mainly to treat calcium deficiencies; and as a food additive with E number of E327. Some cheese crystals consist of calcium lactate. The lactate ion is chiral, with two enantiomers, D (−,R) and L (+,S). The L isomer is the one normally synthesized and metabolized by living organisms, but some bacteria can produce the D form or convert the L to D. Thus calcium lactate also has D and L isomers, where all anions are of the same type. Some synthesis processes yield a mixture of the two in equal parts, resulting in the DL (racemic) salt. Both the L and the DL forms occur as crystals on the surface of aging Cheddar cheese. The solubility of calcium L-lactate in water increases significantly in presence of d-gluconate ions, from 6.7 g/dl) at 25 °C to 9.74 g/dl or more. Paradoxically, while the solubility of calcium L-lactate increases with temperature from 10 °C (4.8 g/dl) to 30 °C (8.5 g/dl), the concentration of free Ca2+ ions decreases by almost one half. This is explained as the lactate and calcium ions becoming less hydrated and forming a complex C3H5O3Ca+. The DL (racemic) form of the salt is much less soluble in water than the pure L or D isomers, so that a solution that contains as little as 25% of the D form will deposit racemic DL-lactate crystals instead of L-lactate. The pentahydrate loses water in a dry atmosphere between 35 and 135 °C, being reduced to the anhydrous form and losing its crystalline character. The process is reversed at 25 °C and 75% relative humidity. Calcium lactate can be prepared by the reaction of lactic acid with calcium carbonate or calcium hydroxide. Since the 19th century, the salt has been obtained industrially by fermentation of carbohydrates in the presence of calcium mineral sources such as calcium carbonate or calcium hydroxide.