Abstract
Aqueous solubility of calcium l-lactate, calcium d-gluconate, and calcium d-lactobionate increases with temperature (10-30 °C investigated), most significantly for the least soluble d-gluconate, while the calcium ion activity of the saturated solutions decreases with temperature, as measured electrochemically, most significantly for the most soluble d-lactobionate. This unusual behavior is discussed in relation to dairy processing and explained by endothermic binding of calcium to hydroxycarboxylate anions determined to have ΔH°ass = (31 ± 3) kJ·mol-1 for l-lactate, (34 ± 2) kJ·mol-1 for d-gluconate, and (29 ± 3) kJ·mol-1 for d-lactobionate in 1:1 complexes with thermodynamic binding constants at 25 °C of Kass = 49 (l-lactate), 88 (d-gluconate), and 140 (d-lactobionate). Quantum mechanical calculations within density functional theory (DFT) confirm the ordering of strength of binding. The complex formation is entropy driven with ΔS°ass > 0, resulting in decreasing calcium ion activity in aqueous solutions for increasing temperature, even for the saturated solutions despite increasing solubility.
| Original language | English |
|---|---|
| Journal | Journal of Agricultural and Food Chemistry |
| Volume | 62 |
| Issue number | 24 |
| Pages (from-to) | 5675-5681 |
| Number of pages | 7 |
| ISSN | 0021-8561 |
| DOIs | |
| Publication status | Published - 18 Jun 2014 |