磷酸氢钙在柠檬酸氢钠水溶液中溶解过程中的部分平衡：自发过饱和增加钙生物可及性的机制,European Food Research and Technology

与其他盐相比，柠檬酸盐中钙的更高生物可及性，通常通过柠檬酸盐等羟基羧酸盐自发形成过饱和钙盐溶液的能力来解释，使用两种模型分析磷酸氢钙在柠檬酸氢钠水溶液中的溶解，然后缓慢沉淀滞后期后的六水合柠檬酸钙。在溶解过程中，以电化学方式测量的钙离子活性增加到最大平台值，溶解时间几乎与初始柠檬酸氢浓度无关，但过饱和度随着柠檬酸氢浓度的增加而强烈增加。通过（i）假设溶解物质之间完全平衡的模型分析了时间依赖性的差异，(ii) 基于耦合微分速率方程的动力学模型，用于使用数值积分在所涉及的溶解物质和沉淀物之间进行转换。与模型 (i) 相比，模型 (ii) 可以量化溶解物质浓度的时间依赖性差异。主要区别在于柠檬酸氢钙的浓度遵循平衡模型中总钙浓度的动态，而浓度在动力学模型中朝着平衡值单调衰减。柠檬酸氢钙被认为对溶解钙的沉淀至关重要，柠檬酸氢钙的浓度决定了滞后期的长度和沉淀速率。

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The higher bioaccessibility of calcium from citrates compared to other salts, often explained by the capacity of hydroxycarboxylates like citrate spontaneously to form supersaturated calcium salt solutions, was analyzed using two models for dissolution of calcium hydrogen phosphate in aqueous sodium hydrogen citrate followed by slow precipitation of calcium citrate hexahydrate after a lag phase. During the dissolution calcium ion activity as measured electrochemically increased to a maximum plateau value for a dissolution time almost independent of initial hydrogen citrate concentration but with a supersaturation degree increasing strongly with increasing hydrogen citrate concentration. The difference in time dependence was analyzed by (i) a model assuming total equilibrium among the dissolved species, and (ii) a kinetic model based on coupled differential rate equations for transformations between involved dissolved species and precipitates using numerical integration. In contrast to model (i), model (ii) could quantify differences in time dependence of the concentration of dissolved species. A major difference was that the concentration of calcium hydrogen citrate follows the dynamics of the total calcium concentration in the equilibrium model, while the concentration decays monotonically towards an equilibrium value in the kinetic model. Calcium hydrogen citrate is concluded to be critical for the precipitation of dissolved calcium with the concentration of calcium hydrogen citrate determining the length of the lag phase and the rate of precipitation. Design of robust supersaturation for functional calcium foods and beverages should accordingly aim of minimizing the concentration of calcium hydrogen citrate.