TY - BOOK
T1 - Supersaturation
T2 - A Proposal for Functional Foods with Improved Calcium Bioavailability
AU - Garcia, André Castilho
PY - 2018
Y1 - 2018
N2 - Calcium is an essential nutrient associated with several vital processes in human organism and, hence, a diet that provides an adequate calcium intake is crucial for a healthy life. Milk and dairy products are good sources of calcium, but the development of novel products and formulations with increased contents of bioavailable calcium are of huge interest. The supersaturation of calcium in different systems could be related to the increased calcium mobility in physiological process, such as bone healing and also could also be used with nutritional perspectives. Therefore, the study of the basic chemistry behind the supersaturation phenomenon can contribute to a general knowledge about calcium nutrition and may even inspire the development of functional foods with increase calcium bioavailability based on this mechanism.
The aqueous solubility of calcium D-saccharate was determined by complexometric titration, as well as the association constant between calcium to D-saccharate ions, which was electrochemically investigated. This complex formation was found to be exothermic and strong in comparison to the endothermic and weaker binding between calcium and other hydroxycarboxylates, like L-lactate, D-gluconate, and D-lactobionate. In supersaturated solutions of calcium D-saccharate prepared by cooling, it was verified that free calcium concentration is only slowly adjusted towards equilibrium, lowering the driving force of precipitation in such solutions. In mixed systems, the complex formation between calcium and D-saccharate ions assists the dissolution of calcium D-gluconate, leading to the formation of spontaneous supersaturated solutions. The slow adjustment of free calcium concentration is suggested to be the stabilizing factor of calcium D-saccharate in supersaturation.
Strongly supersaturated solutions of calcium citrate are formed spontaneously during isothermal dissolution of calcium hydroxycarboxylates by aqueous sodium citrate. The maximal supersaturation was found to decrease for increasing association constants for calcium binding: L-lactate < D-gluconate < citrate. For the dissolution of calcium L-lactate, it was verified a linear relationship between the achieved degree of supersaturation and the amount of added citrate. These supersaturations occur due to a combination of thermodynamic and kinetic effects: stronger complex formation between calcium and citrate ions and slow precipitation rate of calcium citrate. For the supersaturation from calcium L-lactate solutions, the lag phase prior to the precipitation of calcium citrate was shown to be shorter for higher degrees of supersaturation. For calcium D-gluconate and calcium citrate, the lag phases prior to precipitation of calcium citrate were longer and less dependent on the degree of supersaturation.
Sodium hydrogencitrate has been found to assist in the dissolution of calcium hydrogenphosphate, leading to supersaturated solutions in relation to calcium citrate. The minimum amounts of sodium hydrogencitrate required to dissolve increasing amounts of calcium hydrogenphosphate were determined and were shown to be linearly dependent. Solutions prepared combining equimolar concentrations of calcium, phosphate and citrate from different sources resulted in immediate precipitation of amorphous calcium phosphate for solutions with neutral or alkaline conditions or resulted in supersaturation in respect to calcium citrate for solutions with acidic conditions. The acidification of suspensions containing amorphous calcium phosphate and citrate ions may lead to formation of supersaturated solutions in relation to calcium citrate and subsequent precipitation of calcium citrate tetrahydrate. The proposed mechanism for precipitation of calcium citrate is dependent on the pH: for more acidic conditions, it is suggested that precipitation of calcium hydrogencitrate is followed by a solid state conversion to calcium citrate, for less acidic conditions this conversion is suggested to happen prior to the precipitation of calcium citrate. The kinetics of precipitation were investigated using the Avrami model and showed that the crystallization rate is the same for both conditions, which had different predominant citrate species and also different degrees of supersaturation in relation to calcium citrate, but the same total calcium concentration in supersaturated states.
AB - Calcium is an essential nutrient associated with several vital processes in human organism and, hence, a diet that provides an adequate calcium intake is crucial for a healthy life. Milk and dairy products are good sources of calcium, but the development of novel products and formulations with increased contents of bioavailable calcium are of huge interest. The supersaturation of calcium in different systems could be related to the increased calcium mobility in physiological process, such as bone healing and also could also be used with nutritional perspectives. Therefore, the study of the basic chemistry behind the supersaturation phenomenon can contribute to a general knowledge about calcium nutrition and may even inspire the development of functional foods with increase calcium bioavailability based on this mechanism.
The aqueous solubility of calcium D-saccharate was determined by complexometric titration, as well as the association constant between calcium to D-saccharate ions, which was electrochemically investigated. This complex formation was found to be exothermic and strong in comparison to the endothermic and weaker binding between calcium and other hydroxycarboxylates, like L-lactate, D-gluconate, and D-lactobionate. In supersaturated solutions of calcium D-saccharate prepared by cooling, it was verified that free calcium concentration is only slowly adjusted towards equilibrium, lowering the driving force of precipitation in such solutions. In mixed systems, the complex formation between calcium and D-saccharate ions assists the dissolution of calcium D-gluconate, leading to the formation of spontaneous supersaturated solutions. The slow adjustment of free calcium concentration is suggested to be the stabilizing factor of calcium D-saccharate in supersaturation.
Strongly supersaturated solutions of calcium citrate are formed spontaneously during isothermal dissolution of calcium hydroxycarboxylates by aqueous sodium citrate. The maximal supersaturation was found to decrease for increasing association constants for calcium binding: L-lactate < D-gluconate < citrate. For the dissolution of calcium L-lactate, it was verified a linear relationship between the achieved degree of supersaturation and the amount of added citrate. These supersaturations occur due to a combination of thermodynamic and kinetic effects: stronger complex formation between calcium and citrate ions and slow precipitation rate of calcium citrate. For the supersaturation from calcium L-lactate solutions, the lag phase prior to the precipitation of calcium citrate was shown to be shorter for higher degrees of supersaturation. For calcium D-gluconate and calcium citrate, the lag phases prior to precipitation of calcium citrate were longer and less dependent on the degree of supersaturation.
Sodium hydrogencitrate has been found to assist in the dissolution of calcium hydrogenphosphate, leading to supersaturated solutions in relation to calcium citrate. The minimum amounts of sodium hydrogencitrate required to dissolve increasing amounts of calcium hydrogenphosphate were determined and were shown to be linearly dependent. Solutions prepared combining equimolar concentrations of calcium, phosphate and citrate from different sources resulted in immediate precipitation of amorphous calcium phosphate for solutions with neutral or alkaline conditions or resulted in supersaturation in respect to calcium citrate for solutions with acidic conditions. The acidification of suspensions containing amorphous calcium phosphate and citrate ions may lead to formation of supersaturated solutions in relation to calcium citrate and subsequent precipitation of calcium citrate tetrahydrate. The proposed mechanism for precipitation of calcium citrate is dependent on the pH: for more acidic conditions, it is suggested that precipitation of calcium hydrogencitrate is followed by a solid state conversion to calcium citrate, for less acidic conditions this conversion is suggested to happen prior to the precipitation of calcium citrate. The kinetics of precipitation were investigated using the Avrami model and showed that the crystallization rate is the same for both conditions, which had different predominant citrate species and also different degrees of supersaturation in relation to calcium citrate, but the same total calcium concentration in supersaturated states.
UR - https://rex.kb.dk/primo-explore/fulldisplay?docid=KGL01011006737&context=L&vid=NUI&search_scope=KGL&tab=default_tab&lang=da_DK
M3 - Ph.D. thesis
BT - Supersaturation
PB - Department of Food Science, Faculty of Science, University of Copenhagen
ER -
