Calcium-binding capacity of organic and inorganic ortho- and polyphosphates

Abstract

-The aim of this research was to determine the calcium-binding capacity of inorganic and organic ortho-and polyphosphates. This calcium-binding capacity can be used to influence the stability of, for example, casein micelles in dairy systems. Four phosphates were selected: disodium uridine monophosphate (Na 2 UMP, organic orthophosphate), disodium hydrogen phosphate (Na 2 HPO 4 , inorganic orthophosphate), sodium phytate (SP, organic polyphosphate), and sodium hexametaphosphate (SHMP, inorganic polyphosphate). Concentrations of up to 100 mmol·L −1 phosphate were added to a 50 mmol·L −1 CaCl 2 solution. The samples were prepared at pH 8.0 and were analyzed before and after sterilization for calcium-ion activity, conductivity, pH, sediment, and turbidity. Both SHMP and SP are strong chelators, as calcium ions bind to these phosphates in the ratio of 3:1 and 6:1, respectively. Calcium ions also strongly bind to Na 2 HPO 4 , but in a ratio of 3:2 with insoluble Ca 3 (PO 4 ) 2 complexes as result. The equilibrium position of Na 2 UMP is not strong towards the chelated complex, and significant levels of free calcium and free phosphate can exist. An equilibrium constant of 0.29 ± 0.08 L·mol −1 was determined for calcium uridine monophosphate (CaUMP) complexes. Both calculation of the equilibrium constant and analysis on the CaUMP precipitate confirmed a reactivity of 1:1 between calcium and Na 2 UMP. The CaUMP complexes are well soluble at ambient temperature, and insoluble complexes appear after sterilization, because the solubility of CaUMP decreases during heating. Finally, we concluded that the structure of phosphate molecules determines their calcium-binding capacity rather than organic or inorganic origin of phosphates.orthophosphate / polyphosphate / organic phosphate / inorganic phosphate / calcium 摘要 -有机和无机正磷酸盐和多磷酸盐对钙的结合能力○ 本文测定了无机和有机正磷酸 和多磷酸盐对钙的结合能力○ 这种结合能力影响到乳体系中酪蛋白酪胶束的稳定○ 四种 磷酸盐分别为 :尿苷磷酸二钠 (Na 2 UMP，有机正磷酸盐)，磷酸氢二钠 (Na 2 HPO 4 ，无 机正磷酸盐)，肌醇六磷酸钠 (SP，有机多磷酸盐)和六偏磷酸钠 (SHMP，无机多磷酸盐)○ 100 mmol·L −1 的磷酸盐添加到 50 mmol·L −1 的 CaCl 2 溶液中○ 分析了杀菌前后样品在 pH 8.0 的钙离子活度、电导率、pH 值、沉淀值和浊度○ SHMP 和 SP 都是强螯合剂，钙离 子与这些磷酸盐螯合的比分别为 3:1 和 6:1○ 同时，钙离子与 Na 2 HPO 4 结合能力较强，产 生了 3:2 的不溶性 Ca 3 (PO 4 ) 2 混合物○ 平衡状态下的 Na 2 UMP 不能与钙形成稳定的螯合物，存

Effect of calcium chelators on heat coagulation and heat-induced changes of concentrated micellar casein solutions: The role of calcium-ion activity and micellar integrity

“…1). In a previous study, a strong decrease in pH for SHMP in a calcium chloride solution upon heating was observed (De Kort et al, 2009). SHMP hydrolyzes into sodium trimetaphosphate and sodium orthophosphate in acidic conditions (Van Wazer, 1958) and this hydrolysis probably occurred to some extent in the MCI solutions during heating as well.…”

“…As these chelators carry different amounts of negative charges, this results in different calciumbinding capacities (De Kort, Minor, Snoeren, Van Hooijdonk, & Van der Linden, 2009). The concentration ranges of the calcium chelators were based on milliequivalents to obtain an equal amount of charges in the samples.…”

“…The pH meter was calibrated with standard buffer solutions of pH 4.0 and pH 7.0. The calcium-ion activities were obtained by the method as described by De Kort et al (2009).…”

“…Consequently, a strong increase in HCT was measured for the Na 2 UMP samples. Because Na 2 UMP is a relatively weak calciumbinder (De Kort et al, 2009) the viscosity and turbidity of the solutions remained constant at all pH values, implying that the micellar structure was not affected (De Kort et al, 2011). Therefore, it is most likely that the decrease in calcium-ion activity was the main driver for the increase in HCT in Na 2 UMP samples.…”

Modelling ion composition in simulated milk ultrafiltrate (SMUF) II. Influence of pH, ionic strength and polyphosphates

“…3b), indicating the release of protons. De Kort, Minor, Snoeren, Van Hooijdonk, and Van Der Linden (2009) and Vujicic, Batra, and Deman (1967) indicated that the cause of the pH drop is due to the replacement of hydrogen by calcium from the polyphosphates. However, according to De Kort et al (2009), SHMP has been recognised as a cyclic compound with six metaphosphate monomers (NaPO 3 ) 6 , as shown in Fig.…”