title: Aqueous solubility of calcium L-lactate, calcium D-gluconate, and calcium D-lactobionate: importance of complex formation for solubility increase by hydroxycarboxylate mixtures.
abstract: Among the calcium hydroxycarboxylates important for cheese quality, D-lactobionate [Ksp = (7.0 ± 0.3) × 10(-3) mol(3) L(-3)] and L-lactate [Ksp = (5.8 ± 0.2) × 10(-3) mol(3) L(-3)] were found more soluble than D-gluconate [Ksp = (7.1 ± 0.2) × 10(-4) mol(3) L(-3)], as indicated by the solubility products determined electrochemically for aqueous 1.0 M NaCl at 25.0 °C. Still, solubility of calcium L-lactate increases by 45% in the presence of 0.50 M sodium D-gluconate and by 37% in the presence of 0.50 M sodium D-lactobionate, while solubility of calcium D-gluconate increases by 66 and 85% in the presence of 0.50 M sodium L-lactate and 0.50 M sodium D-lactobionate, respectively, as determined by complexometric titration. Sodium L-lactate and sodium D-gluconate have only little influence on solubility of calcium D-lactobionate. The increased solubility is described quantitatively by calcium binding to D-gluconate (K1 = 14 ± 3 mol(-1) L) in 1.0 M NaCl at 25 °C, D-lactobionate (K1 = 11 ± 2 mol(-1) L), and L-lactate (K1 = 8 ± 2 mol(-1) L), as indicated by the association constants determined electrochemically. In mixed hydroxycarboxylate solutions, calcium binding is quantitatively described by the geometric mean of the individual association constants for both aqueous 1.0 and 0.20 M NaCl, indicating a 1:1 stoichiometry for complex formation.
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.forename: Merete Bøgelund
authors.initials: MB
authors.lastname: Munk
authors.forename: Leif H
authors.initials: LH
authors.lastname: Skibsted
mesh_terms: D017610:Calcium Compounds / Q000737:chemistry*; D002125:Calcium Gluconate / Q000737:chemistry*; D002611:Cheese / Q000032:analysis*; D004187:Disaccharides / Q000737:chemistry*; D005503:Food Additives / Q000737:chemistry*; D007773:Lactates / Q000737:chemistry*; D012995:Solubility; D012996:Solutions / Q000737:chemistry
chemical_list: D017610:Calcium Compounds; D004187:Disaccharides; D005503:Food Additives; D007773:Lactates; D012996:Solutions; C110051:calcium lactate; C005608:lactobionic acid; D002125:Calcium Gluconate