Volumetric properties of disodium dihydrogen pyrophosphate aqueous solution from 283.15 to 363.15 K at 101.325 kPa
Introduction
There are various food additives used in foodstuffs imparting features such as color, flavour, preservation, thickeners, stabilizers, taste, conservation, emulsifier, or acidity regulation. Among those phosphates or polyphosphates are not renewable additives, which are involved in many metabolic pathways and are naturally found in the form of organic esters in foods like egg, meat, potatoes, and cereals (Thangavelu, Kerry, Tiwari, & McDonnell, 2019). Generally, polyphosphates are products of polycondensation of inorganic orthophosphates prepared at high temperatures. The term “condensed inorganic phosphates” is applied to phosphorus compounds with various numbers of PO4 groups linked together by oxygen bridges (Raskovic, 2007). Condensed inorganic phosphates with linear structures are accurately called polyphosphates possessing the general elementary composition [PnO3n+1](n+2) –. Therefore, a metal salt of H4P2O7 is pyrophosphate, H5P3O10 is tripolyphosphate (triphosphate), and H6P4O13 is tetraphosphate. Sodium polyphosphates are well known as suitable substances to have various applications. Especially sodium trimetaphosphate and sodium tripolyphosphate are widely used for phosphorylating starch that may have a significant effect on the pasting property and used as a buffering agent sequestrant or dispersant (Shukri and Shi, 2017, Xiong et al., 2010).
However, among sodium polyphosphate, disodium dihydrogen pyrophosphate or sodium acid pyrophosphate, Na2H2P2O7, is used in the food industry as a good additive. This type of phosphate is a promising product owing to its remarkable performances commonly used in food processing such as in canned seafood, cured meat, and potato products, as well as to adjusting pH, maintaining color, baking powder, and leavening agent for improving water-holding capacity (Abd-Elhakim et al., 2018, Blekas, 2016, Jastrzebska, 2011, Long et al., 2011, Sickler et al., 2013). Additionally, the polyphosphates play a crucial role in lipid oxidation of ground beef when mixed with sodium tripolyphosphate (Sickler et al., 2013). Moreover, it is expected that 0.5% phosphate incorporation into ground beef before cooking aids to store products for a more extended period of time, which has significant benefits. Sodium pyrophosphate along sodium tripolyphosphate, sodium hexametaphosphate, and trisodium phosphate increased cooking yield, improved pasting viscosity, and reduced cooking loss of wheat flour because of cross-linking between hydroxyl groups of phosphate salts and starch (Chen et al., 2019).
In fact, Na2H2P2O7 was recognized to be a good candidate because of its multifunctional contribution to preventing struvite stones formation in the kidney or bladder, inhibiting the formation of calcium oxalate as well as utilizing as a bone-pain palliation agent for the treatment of bone metastases (Abbasi, 2015, Das et al., 2017). Pyrophosphate ions are based on the promising phosphate material applied successfully as a degradable osteoconductive in calcium phosphate cement resorption and bone generation (Grover et al., 2013).
Likewise, simple orthophosphates including monosodium phosphate, disodium phosphate, and dipotassium phosphate have also been widely used in foods as an ingredient and functional additive for retention of water, buffering agent, prevent the discoloration of fresh noodles, promote starch gelatinization and reduce a cooking loss (Chen et al., 2019, Fu, 2008, Goncalves and Rebeiro, 2008). Furthermore, there are reports about density, thermal expansion coefficient, apparent molar volume, and standard partial volume of aqueous solutions of some sodium orthophosphates at different temperatures and pressures (Woolston et al., 2008, Zhang et al., 2015). For example, in the literature (Zhang et al., 2015), the solubility and physicochemical properties of NaH2PO4 were measured in sodium chloride solutions (0 to 2.66 mol·kg−1), phosphoric acid solutions (0 to 2.79 mol·kg−1), and mixed solutions of sodium chloride and phosphoric acid solutions at temperatures of T = 298.15 and 313.15 K respectively. Densities and apparent molar volumes of aqueous NaH2PO4 (0.1 to 2.1 mol·kg−1), Na2HPO4 (0.1 to 0.5 mol·kg−1), and Na3PO4 (0.4 to 0.6 mol·kg−1) have been determined at temperatures from 373 K to 598 K at constant 15 MPa pressure (Woolston et al., 2008).
Although remarkable and advanced applications of disodium dihydrogen pyrophosphate in daily life have been investigated, unfortunately, there are few reports about the thermodynamic properties of pyrophosphates. Therefore, investigation of the physicochemical properties of sodium acid pyrophosphate is still relevant.
The volumetric properties Na2H2P2O7 need to be investigated for food chemistry and solution chemistry. In the present study, density, thermal coefficient expansion, apparent, partial molar volumes, and expansibilities of disodium dihydrogen pyrophosphate aqueous solutions in the concentration ranging from 0.08706 to 0.88402 mol·kg−1 have been investigated at 5 K intervals from 283.15 K to 363.15 K at 101.325 kPa. Data obtained can be used for the Pitzer ion-interaction theory to predict different thermodynamic processes and equilibrium in these aqueous solutions (Pitzer, 1973).
Section snippets
Materials and solution preparation
Na2H2P2O7 was purchased from Aladdin Co., Ltd. (China) and had a standard reagent grade with a purity of 0.995, which was further recrystallized before use. The purity of recrystallized Na2H2P2O7 was 0.999 in mass fraction, which was analyzed by inductively coupled plasma-optical emission spectrometry (ICP-OES, Prodigy, Leman Corporation, USA) with an uncertainty of ± 0.0072 in mass fraction. The purity, source, and CAS number of Na2H2P2O7 used in the experiments are listed in Table S1.
The
Densities and apparent molar volume of Na2H2P2O7 aqueous solution
The addition of phosphates in food as an ingredient is more attention while maintaining drinks, juice, sauce with desired densities and viscosity. Measured densities of Na2H2P2O7 aqueous solutions at different temperatures and molalities are listed in Table 1.
The apparent molar volumes based on the relationship of the measured densities of pure water and Na2H2P2O7 solution were calculated by:where mi is the molality (mol·kg−1) of the solute in the solution. Mi is the
Density and apparent molar volumes of Na2H2P2O7 aqueous solution
In general practice, food phosphates solution is heated during diary production for imparting various properties such as buffering, water-binding, emulsification, and protein dispersion properties. Table 1 shows that values of densities for Na2H2P2O7 aqueous solutions decrease smoothly with increasing temperature, while it increases drastically with the increase of molality. The behavior of the density value is affected by mi and T monotonically. A rise in temperature contributes to the
Conclusions
The thermal expansion coefficient, apparent molar volumes, apparent molar volume expansibilities and partial molar volumes of the binary systems of Na2H2P2O7 + H2O on the basis of density values from 283.15 to 363.15 K and molality range from diluted to the saturated solution at 101.325 kPa were reported for the first time. It was revealed that plots of the variables mentioned above have regular changes depending upon the molality and temperature. The thermal expansion coefficient increases
CRediT authorship contribution statement
Umarbek Alimov: Formal analysis, Investigation, Writing - original draft. Kaiyu Zhao: Resources, Software. Jiayin Hu: . Yafei Guo: Project administration, Visualization, Supervision. Lingzong Meng: Software, Methodology, Data curation. Xiuyun Pan: Project administration. Tianlong Deng: Conceptualization, Methodology, Funding acquisition, Writing - review & editing.
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
Financial supports from the National Natural Science of China (22073068 and 21773170), Special Major Project of the Innovation Technology Hubei Province (2019ACA149 and YJYXM2020000009) and the Yangtze Scholars and Innovative Research Team in Chinese University (IRT_17R81) are acknowledged.
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