title: Calcium d-Saccharate: Aqueous Solubility, Complex Formation, and Stabilization of Supersaturation.
abstract: Molar conductivity of saturated aqueous solutions of calcium d-saccharate, used as a stabilizer of beverages fortified with calcium d-gluconate, increases strongly upon dilution, indicating complex formation between calcium and d-saccharate ions, for which, at 25 °C, Kassoc = 1032 ± 80, ΔHassoc° = −34 ± 6 kJ mol–1, and ΔSassoc° = −55 ± 9 J mol–1 K–1, were determined electrochemically. Calcium d-saccharate is sparingly soluble, with a solubility product, Ksp, of (6.17 ± 0.32) × 10–7 at 25 °C, only moderately increasing with the temperature: ΔHsol° = 48 ± 2 kJ mol–1, and ΔSassoc° = 42 ± 7 J mol–1 K–1. Equilibria in supersaturated solutions of calcium d-saccharate seem only to adjust slowly, as seen from calcium activity measurements in calcium d-saccharate solutions made supersaturated by cooling. Solutions formed by isothermal dissolution of calcium d-gluconate in aqueous potassium d-saccharate becomes spontaneously supersaturated with both d-gluconate and d-saccharate calcium salts, from which only calcium d-saccharate slowly precipitates. Calcium d-saccharate is suggested to act as a stabilizer of supersaturated solutions of other calcium hydroxycarboxylates with endothermic complex formation through a heat-induced shift in calcium complex distribution with slow equilibration upon cooling.
authors.affiliation: Food Chemistry, Department of Food Science, University of Copenhagen , Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.|Insituto Federal de Educação, Ciência e Tecnologia de São Paulo , Campus Capivari, Avenida Doutor Ênio Pires de Camargo, 2971, São João Batista, Capivari, São Paulo 13360-000, Brazil.
authors.forename: André C
authors.initials: AC
authors.lastname: Garcia
authors.affiliation: Food Chemistry, Department of Food Science, University of Copenhagen , Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
authors.forename: Martina
authors.initials: M
authors.lastname: Vavrusova
authors.affiliation: Food Chemistry, Department of Food Science, University of Copenhagen , Rolighedsvej 30, DK-1958 Frederiksberg C, Denmark.
authors.forename: Leif H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D001628:Beverages; D055598:Chemical Phenomena; D004355:Drug Stability; D004563:Electrochemistry; D005937:Glucaric Acid / Q000737:chemistry*; D005942:Gluconates / Q000737:chemistry; D012995:Solubility; D012996:Solutions / Q000737:chemistry; D013816:Thermodynamics; D014867:Water
chemical_list: D005942:Gluconates; D012996:Solutions; D014867:Water; D005937:Glucaric Acid; C030691:gluconic acid
keywords: calcium complexes; calcium d-gluconate; calcium d-saccharate; calcium salt solubility; spontaneous supersaturation