Abstract Calcium binding to o-phospho- l -serine (OPS), important for calcium distribution during milk processing and for calcium bioavailability, was studied electrochemically for different conditions of temperature, pH and ionic strength in combination with quantum mechanical calculations (DFT) using l -serine (Ser) as a reference compound. Calcium binding increases strongly with increasing pH for both Ser and OPS. pH dependent binding of calcium ions was resolved using pKa values into, respectively, Kass,1, Kass,2 and Kass,3 = 20, 37 and 180 L mol−1 with ΔH0ass,1 ΔH0ass,2 ΔH0ass,3 = 16, −7.4 and −11 kJ mol−1 for binding to OPS−, OPS2− and OPS3− at an ionic strength 0.2 and 15 °C. Dissolution of CaOPS at milk pH was endothermic. The shift from endothermic binding of calcium to OPS at low pH to exothermic binding at higher pH, corresponding to a shift from hydrophobic interaction (phosphate ester) to ionic binding (carboxylate/amino chelation), was supported by DFT.

中文翻译：

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在牛奶加工条件下，受温度、pH 值和离子强度影响的钙与 l-丝氨酸和 o-磷酸-l-丝氨酸的结合

摘要 钙与 o-磷酸-l-丝氨酸 (OPS) 的结合对牛奶加工过程中的钙分布和钙的生物利用度很重要，在不同的温度、pH 值和离子强度条件下，结合量子力学计算 (DFT) 进行了电化学研究。 l-丝氨酸（Ser）作为参考化合物。Ser 和 OPS 的钙结合随着 pH 值的增加而显着增加。钙离子的 pH 依赖性结合使用 pKa 值分别解析为 Kass,1、Kass,2 和 Kass,3 = 20、37 和 180 L mol-1，其中 ΔH0ass,1 ΔH0ass,2 ΔH0ass,3 = 16, - 7.4 和 -11 kJ mol-1 用于在 0.2 和 15 °C 的离子强度下与 OPS-、OPS2- 和 OPS3- 结合。CaOPS 在牛奶 pH 值下的溶解是吸热的。从钙在低 pH 下吸热结合到 OPS 转变为在较高 pH 下放热结合，