Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK -1958 Frederiksberg C, Denmark; Instituto Federal de Educação, Ciência e Tecnologia de São Paulo, Campus Capivari. Avenida Doutor Ênio Pires de Camargo, 2971 - São João Batista, - CEP: 13360-000 -Capivari, SP, Brazil.
Department of Food Science, University of Copenhagen, Rolighedsvej 30, DK -1958 Frederiksberg C, Denmark.
Food Res Int. 2018 May;107:195-205. doi: 10.1016/j.foodres.2018.02.020. Epub 2018 Feb 10.
Dissolution of amorphous calcium phosphate (ACP) in aqueous citrate at varying pH has been studied with perspective of increasing availability of calcium from sidestreams of whey protein, lactose and/or cheese production or on development of new functional foods. ACP formed as an initial precipitate in 0.10 mol L equimolar aqueous calcium chloride, sodium citrate, and sodium hydrogenphosphate was used as model for mineral residues formed during milk processing. Upon acidification of the ACP suspension by hydrochloric acid decreasing pH from 6.5 to 4.5, the transformations of ACP occurred through an 8 h period of supersaturation prior to a slow precipitation of calcium citrate tetrahydrate. This robust supersaturation, which may explain increased availability of calcium phosphates in presence of citrate, presented a degree of supersaturation of 7.1 and was characterized by precipitation rates for 0.10 mol L equimolar aqueous calcium chloride, sodium hydrogencitrate, and sodium hydrogenphosphate with pH 5.5, and for 0.10 mol L equimolar aqueous calcium chloride, sodium hydrogencitrate, and sodium dihydrogenphosphate with pH 4.1, with a degree of supersaturation of 2.7. The crystallization processes were similar according to Avrami's model with a half-life for precipitation of approximately 5 h independent of the degree of supersaturation. Ion speciation based on measurement of pH, and total concentrations of calcium, phosphate and citrate, and of conductivity and calcium ion activity during precipitation indicates a low driving force for precipitation with calcium citrate complex dominating at pH 5.5 and calcium hydrogencitrate complex dominating at pH 4.1. Calcium hydrogencitrate is suggested to be the species involved in the crystal growth followed by solid state transformation to calcium citrate tetrahydrate.
在不同 pH 值条件下，研究了柠檬酸溶液中无定形磷酸钙（ACP）的溶解情况，以期提高乳清蛋白、乳糖和/或奶酪生产副产物中钙的利用率，或开发新型功能性食品。以在牛奶加工过程中形成的矿物质残余物为模型，使用在等摩尔浓度的氯化钙、柠檬酸钠和磷酸氢二钠的水溶液中形成的初始 ACP 沉淀。用盐酸酸化 ACP 悬浮液，将 pH 值从 6.5 降低至 4.5，ACP 的转化发生在过饱和度持续 8 小时之后，随后是缓慢沉淀四水合柠檬酸钙。这种稳健的过饱和度可能解释了在柠檬酸存在下磷酸钙的可用性增加，其过饱和度为 7.1，并具有以下特征：在 pH 值为 5.5 时，0.10 mol/L 等摩尔浓度的氯化钙、柠檬酸钠和磷酸氢二钠的沉淀速率，以及在 pH 值为 4.1 时，0.10 mol/L 等摩尔浓度的氯化钙、柠檬酸钠和磷酸二氢钠的沉淀速率，过饱和度为 2.7。根据 Avrami 模型，结晶过程相似，沉淀的半衰期约为 5 小时，与过饱和度无关。根据 pH 值、钙离子、磷酸根离子和柠檬酸根离子的总浓度以及沉淀过程中的电导率和钙离子活度的测量，离子形态表明沉淀的驱动力较低，在 pH 值为 5.5 时，柠檬酸钙络合物占主导地位，在 pH 值为 4.1 时，柠檬酸氢钙络合物占主导地位。推测柠檬酸氢钙是参与晶体生长的物质，随后通过固态转化为四水合柠檬酸钙。
