Soluble Calcium Phosphate Research Articles

Relationship between phosphate scales and silica fouling in wastewater RO membrane systems

Precipitation of calcium phosphate scale on reverse osmosis (RO) membranes continues to be a major challenge for wastewater recycling facilities. In most cases, antiscalant is dosed in combination with sulfuric acid because calcium phosphate solubility improves at lower pH. Several waste water RO plants in California that have attempted to reduce the costly acid dosing have experienced fast scale formation that has offset any savings with downtime and expensive cleaning chemicals. Online cleanings were attempted by reducing the pH to 6 for 1 week in order to reduce downtime; however, they did not fully restore flux in the tail elements and performance progressively declined over time. When these membranes were autopsied, silica was surprisingly the predominant deposit on the membrane surface, even though brine silica concentrations were only in the range of 130–160 ppm. An extensive study was conducted to simulate these conditions in a laboratory setting. Tests were conducted using various antiscalants av...

Absolute and age-dependent elevations of serum calcium and phosphate and their products in clinical opiate dependence

Context: Chronic opiate dependence has been linked with premature appearance of many chronic age-related disorders and blood-borne biomarkers of ageing. Objective: To determine if clinical opiate substance use disorder (SUD) was associated with elevations of serum calcium and phosphate and their various products. Methods: Chemical pathology records were traced retrospectively. Results: A total of 1747 SUD patients were compared with 6454 non-SUD (NSUD) patients. The mean (±SD) ages were 32.06 ± 6.64 and 32.13 ± 8.12 years, respectively (p = 0.74). The two groups were 69.5% and 54.6% male (p < 0.000 1). The mean serum calcium levels were 2.40 ± 0.11 and 2.37 ± 0.10 mmol/l (p < 0.000 1). This significant difference was unrelated to albumin levels, and also occurred for phosphate: 1.17 ± 0.22 and 1.15 ± 0.22 (p < 0.000 1). Both the calcium-phosphate product and the calcium-phosphate solubility product were also elevated. These elevations persisted at multiple regression against age in both additive and interactive models with age (most p < 0.000 1). At age 35, the corrected calcium and phosphate were equivalent to a 75.1% and 13.5% age advancement, respectively. Conclusion: Opiate dependence is associated with significant elevations of calcium and phosphate both in absolute terms, and after correction for serum albumin and age. Their product and their solubility product are similarly elevated.

New efficient DNA extraction method to access the microbiome of Ricinus communis seeds

Ricinus communis (castor bean) seeds are used to produce an alcohol-soluble oil that is used in more than 400 industrial processes. Despite its economic importance, there has been little research on the endophytic microbiota of castor bean seeds. This microbiota is important for plant metabolic processes and may have considerable biotechnological potential, such as production of lipases and plant growth promoter agents. We evaluated several DNA extraction methodologies in order to access the microbial diversity of castor bean through a metagenomic approach. Based on our observations, we developed a new methodology that takes advantage of the low solubility of calcium phosphates and the high affinity of these phosphates for proteins and polysaccharides. The extracted DNA quality was evaluated by PCR, using a selective primer pair for bacterial and mitochondrial 16S rDNA genes (799F and 1492R). We found this methodology quantitatively and qualitatively more efficient than the other approaches. In evaluating this new extraction methodology, we found that the difficulties of DNA extraction from castor bean seeds, such as abundant oil, polysaccharides, phenolic compounds, and plant enzymes, could be overcome. The resulting extracts had high concentration and purity, and they were obtained faster than with previous methods. The samples contained virtually all of the DNA, including the microbial DNA; this was validated by PCR analysis.

Phase composition control of calcium phosphate nanoparticles for tunable drug delivery kinetics and treatment of osteomyelitis. II. Antibacterial and osteoblastic response

Osteomyelitis has been traditionally treated by the combination of long-term antibiotic therapies and surgical removal of diseased tissue. The multifunctional material was developed in this study with the aim to improve this therapeutic approach by: (a) enabling locally delivered and sustained release of antibiotics at a tunable rate, so as to eliminate the need for repetitive administration of systemically distributed antibiotics; and (b) controllably dissolving itself, so as to promote natural remineralization of the portion of bone lost to disease. We report hereby on the effect of previously synthesized calcium phosphates (CAPs) with tunable solubilities and drug release timescales on bacterial and osteoblastic cell cultures. All CAP powders exhibited satisfying antibacterial performance against Staphylococcus aureus, the main causative agent of osteomyelitis. Still, owing to its highest drug adsorption efficiency, the most bacteriostatically effective phase was amorphous CAP with the minimal inhibitory concentration of less than 1 mg/mL. At the same time, the positive cell response and osteogenic effect of the antibiotic-loaded CAP particles was confirmed in vitro for all the sparsely soluble CAP phases. Adsorption of the antibiotic onto CAP particles reversed the deleterious effect that the pure antibiotic exerted on the osteogenic activity of the osteoblastic cells. The simultaneous osteogenic and antimicrobial performance of the material developed in this study, altogether with its ability to exhibit sustained drug release, may favor its consideration as a material base for alternative therapeutic approaches to prolonged antibiotic administration and surgical debridement typically prescribed in the treatment of osteomyelitis.

Phase composition control of calcium phosphate nanoparticles for tunable drug delivery kinetics and treatment of osteomyelitis. I. Preparation and drug release

Developed in this study is a multifunctional material for simultaneous osseoinduction and drug delivery, potentially applicable in the treatment of osteomyelitis. It is composed of agglomerates of nanoparticles of calcium phosphate (CAP) with different monophasic contents. The drug-loading capacity and the release kinetics were investigated on two model drug compounds with different chemical structures, sizes, and adsorption propensities: bovine serum albumin and fluorescein. Loading of CAP powders with small molecule drugs was achieved by physisorption and desiccation-induced agglomeration of nanoparticulate subunits into microscopic blocks. The material dissolution rate and the drug release rate depended on the nature of the CAP phase, decreasing from monocalcium phosphate to monetite to amorphous CAP and calcium pyrophosphate to hydroxyapatite. The sustained release of the two model drugs was shown to be directly relatable to the degradation rate of CAP carriers. It was demonstrated that the degradation rate of the carrier and the drug release kinetics could be made tunable within the time scale of 1-2 h for the most soluble CAP phase, monocalcium phosphate, to 1-2 years for the least soluble one, hydroxyapatite. From the standpoint of antibiotic therapy for osteomyelitis, typically lasting for 6 weeks, the most prospective CAP powder was amorphous CAP with its release time scale for a small organic molecule, the same category to which antibiotics belong, of 1-2 months under the conditions applied in our experiments. By combining these different CAP phases in various proportions, drug release profiles could be tailored to the therapeutic occasion.

Preparation of injectable auto-forming alginate gel containing simvastatin with amorphous calcium phosphate as a controlled release medium and their therapeutic effect in osteoporosis model rat

Highly soluble amorphous calcium phosphate powder (ACP) was added to the alginate gel as a buffering agent, in an attempt to enable widely controlled release while avoiding an acidification of the gel-environment. Therapeutic effects of the ACP-containing alginate gel which slowly releases a drug, simvastatin, on osteoporosis model rats were examined. A model drug, simvastatin, incorporated in the alginate gel with ACP up to 0.5%, was continuously released for a long time under the acidic condition. The release rate was controlled by the amount of ACP, serving as a buffer to suppress acidity. When the alginate solution intramuscularly injected in the rat, a soft gel was formed in the injected site. Simvastatin released from the gel containing 0.5% of ACP showed high therapeutic effect on osteoporosis rat. Thus, the present injectable long-sustained release system is expected to be a novel drug delivery controlling device.

Characterization and functional properties of soybean high-molecular-mass polysaccharide complex

Soybean soluble polysaccharide (SSPS), extracted from the by-product obtained during isolation of soybean protein, is an anionic polysaccharide that stabilizes milk proteins under acidic conditions. We developed a high-molecular-mass complex of SSPS cross-linked via phosphate (SSPS-HC; absolute molecular weight = 2850 kg/mol, radius of gyration = 106 nm), and found that it has different protein stabilization properties when compared with the original SSPS (absolute molecular weight = 550 kg/mol, radius of gyration = 36 nm). The objective of this work was not only to study the rheological properties of SSPS-HC, but also clarify its protein-stabilizing properties in comparison with SSPS; if molecular mass or negative charge affected protein dispersion. Irrespective of high-molecular-mass, SSPS-HC possessed similar rheological properties to SSPS such as low viscosity in aqueous solution. The absolute negative charges of SSPS-HC measured by a zeta potential analyzer at pH range of 2.0–7.0 were higher than those of SSPS. Acidified milk drinks prepared with 8.4% non-fat milk solids and 0.4% SSPS-HC or SSPS showed low viscosity and small protein particle size, and did not aggregate for 14 days. The thickness of the hydrated layer, which was formed on the surface of protein particles by SSPS molecules measured after hemicellulase treatment with DLS (dynamic light scattering), was estimated to be about 89 nm for SSPS-HC and 33 nm for SSPS. These numerical values were in good relation to the molecular diameter of SSPS-HC and SSPS in aqueous solution measured by DLS and AFM image, and suggested that protein particles were dispersed and the hydrated monolayer made on the surface of protein particles by SSPS-HC or SSPS molecules prevented aggregation. However, stabilizing pH ranges were different with stability of SSPS-HC at pH range of 4.0–4.8 and stability for SSPS at pH range of 3.6–4.2. In addition to the difference in the molecular mass and absolute negative charge, the phosphate groups of SSPS-HC were possibly influenced on the protein-dispersing property approximately at isoelectric point of milk protein; SSPS-HC prevent aggregation of casein by accelerating solubility of calcium phosphate under acidic conditions as is already reported in the starches phosphorylated.

The chemistry of thiosulfate and vascular calcification

Thiosulfate has been shown to inhibit vascular calcification in uremic rats and may inhibit calcification in humans with end-stage renal disease but whether this is due to a systemic or local action is unknown. The underlying mechanism is also unclear but complexation of calcium ions has been proposed. In vitro assays were used to determine the effect of thiosulfate on vascular calcification and hydroxyapatite formation. Thiosulfate (EC50: 1-2 mM) prevented calcification of injured or devitalized aortas but not uninjured aortas, and similar results were obtained with sulfate. There was no effect on reversal of calcification. Measurements with an ion-sensitive electrode (corrected for changes in ionic strength) revealed a very weak interaction between thiosulfate and Ca(2+) (K(a) = 10.9 ± 1.0 × 10(-6) M(-1)) that resulted in a 4% decrease in ionized Ca(2+) in culture medium at 5 mM thiosulfate and a corresponding 5% increase in the solubility product for calcium-phosphate. Adjustment of the total Ca(2+) concentration to account for this did not prevent the inhibition of aortic calcification by thiosulfate. Thiosulfate did not inhibit hydroxyapatite formation from seed crystals or the calcification of purified elastin and did not alter medium pH. Thiosulfate inhibits vascular calcification at millimolar concentrations through a direct extracellular effect that does not require intact smooth muscle cells but is related to cellular injury. This effect is not specific for thiosulfate since sulfate has similar properties. Inhibition cannot be explained by effects on ionized calcium, calcium-phosphate solubility, pH, oxidative stress or hydroxyapatite formation.

Culturable bacteria in hydroponic cultures of moss Racomitrium japonicum and their potential as biofertilizers for moss production

The use of Racomitrium japonicum, a drought resistant bryophyte used for roof-greening, is gradually increasing. However, its utilization is hampered by slow growth rate. Here we isolated culturable bacteria from hydroponic cultivation samples to identify isolates that could promote moss growth. Most of the isolates belonged to Pseudomonas, Rhodococcus, and Duganella species. The isolates were biochemically characterized according to their type of interaction with plants, i.e., production of auxin, siderophores, or hydrogen cyanate, growth in the absence of an added nitrogen source, calcium phosphate solubilization, utilization of sugars, polymers, or aliphatic compounds, and antifungal activity. The isolates were applied to sterile protonemata and non-sterile adult gametophytes of R. japonicum to evaluate their effect on plant growth. Furthermore, we isolated fungi that inhibited moss growth. Our results suggest that the microbial community structure in hydroponic cultures is important to stabilize moss production and the isolates that promote moss growth have potential to be utilized as biofertilizers for moss production.

Dynamics of crystallization and dissolution of calcium orthophosphates at the near-molecular level

Although extensive investigations of biogenic and geological calcium phosphate crystallization/dissolution and their phase transformations have been performed, the mechanisms of crystallization and dissolution of sparingly soluble calcium phosphates in geological settings have not been completely determined at the near-molecular level. In particular, an understanding of the physical-chemical processes at the earliest nucleation stage and the subsequent crystal surface dynamics in soil solutions is lacking. This review focuses on the earliest events in homo/heterogeneous nucleation from an initial supersaturated solution phase, the subsequent growth of calcium phosphate phases, and the relevant influences of the presence of additional inorganic and organic molecules in both geological and biological settings. These studies have implications for the understanding of the complex processes of calcium phosphate transformations in soils, and provide possible physical-chemical mechanisms for the biogeochemical behavior of phosphorus at the near-molecular level.

Characterization and dissolution of functionalized amorphous calcium phosphate biolayers using single-splat technology

New processing routes and characterization techniques underpin further growth of biomaterials for improved performance and multifunctionality. This study investigates the characteristics and solubility of amorphous calcium phosphate (ACP) printed splats. Splats made from 20 to 60 μm molten hydroxyapatite particles were classified for shape (rounded/splashed) and cracking. Recoil of the spread droplet created a bowl-shaped splat. This has previously not been observed and could be related to the longer solidification time associated with solidification to an ACP. A central depression was created from 20 μm particles, but a bowl-shaped splat from 60 μm particles. Cracking was more prevalent for splats that solidified with an edge discontinuity. Splats immersed in pH 7.3 tris buffer displayed dissolution followed by cracking. Cracking continued over a period of 15 min as dissolution induced more cracks. Further degradation occurred by delamination of splat segments. Delamination accelerated the process of splat removal. Applied to thermal spray coatings, this highlights topography and dissolution at the splat level. The use of separate splats can potentially be used as a biolayer where splats are separate, in a line or on top of each other.

Effect of Ampicillin as Bacteriostats on the Performance of Phosphate Solubilizing &lt;i&gt;Rhizobium. Meliloti&lt;/i&gt; Inoculants

The aim of this study was to evaluate the effect of Ampicillin as bacteriostats on the number of P solubilizing and antibiotic-anti-Rhizobium. meliloticells and contamination in inoculants during one year storage, and plant promotion ability of subgeneration cells of antibiotic-resistant phosphate-solubilizing R. meliloti strain LW107 growth on YMA plates containing different concentrations of ampicillin were also investigated. In the first experiment, 100 mg liter-1 ampicillin was added in inoculants, number of R.meliloticells and contamination in inoculants were investigated at two temperatures, using both liquid and peat based solid inoculants in experiment. Statistical design was a complete randomized block in a factorial 2×2×2 experimental arrangement with 4 replicates. Results show that there are various viable cells and contamination levels in inoculants. The ampicillin increased R.melilotiLW107 viable cells and inoculants stored at low temperature with lesser contamination when ampicillin been added. To clarify whether ampicillin affect the main character of R.melilotiLW107 cells, the ability of calcium phosphate solubilization and IAA production in ampicillin-containing conditions was determined. Results indicated that the ability of calcium phosphate solubilization and IAA production have no significant difference on 6th generation cells of R.melilotiLW107 between the growth plates and the lack of ampicillin. In the third experiment, the plant growth promotion of the ampicillin-containing inoculants on alfalfa seedlings was determined in sterile sand conditions in a temperature-controlled growth chamber at 20 -25°C for 35 days. We also found that no significant difference on nodule numbers between diluted liquids ampicillin-containing inoculants and the common liquid inoculants containing no ampicillin, but plant growth and efficiency of nitrogen-fixing responded to undiluted liquids inoculants containing ampicillin with a decrease in biomass and nitrogenase activity indicating that the five-fold dilutions of the ampicillin-containing inoculants are necessary for applications.

Efficacy of polyphasic calcium phosphates as a direct pulp capping material

Objectives Polyphasic calcium phosphates (Poly-CaP), a complex of hydroxyapatite (HAp) and soluble calcium phosphates including α-tricalcium phosphate and tetracalcium phosphate, demonstrate promoting effects on hard tissue formation by osteoblasts. We hypothesized that a Poly-CaP block with a soluble calcium phosphates phase on one side and an insoluble HAp phase on the other side is useful for vital pulp therapy as it may promote dentin regeneration and provide the surface effective to achieve sealing. The purpose of this study was to investigate the efficacy of Poly-CaP as a direct pulp capping material by examining the Ca-release profile, the in vivo ability to induce reparative dentinogenesis, and the bonding of HAp surface with adhesive systems. Methods Poly-CaP prepared by annealing crude HAp disc was immersed in buffer solution at pH 7.4 or 4.0, and the concentration of Ca released was measured until 15 days. The pulp of 9-week-old Wister rat molar was exposed and capped with Poly-CaP or HAp block, and dentin bridge formation and pulpal inflammation was evaluated histopathologically after 2 or 4 weeks. Etch & rinse or self-etching adhesive was bonded to HAp surface, and the interface was observed using SEM. Results Poly-CaP exhibited continuous release of Ca with significantly greater amount than HAp at both pH conditions ( P < 0.05, Student's t-test). Animal tests demonstrated formation of complete dentin bridge at higher rate for Poly-CaP compared with HAp after 4 weeks ( P < 0.05, Steel–Dwass test). Impregnation of resin into etched HAp surface, with production of intimate contact at the bonding interface, was seen for all adhesives. Conclusions Poly-CaP is a potentially useful material for direct pulp capping with the advantages to promote dentin bridge formation and to provide tight sealing by adhesives.

Nutrient Balance at Integrated Nutrient Management on Lowland Rice Which is Dominated by 1:1 Clay Mineral for High Potential Rice Yields

Nutrient Balance at Integrated Nutrient Management on Lowland Rice Which is Dominated by 1:1 Clay Mineral for High Potential Rice Yields

Theoretical Model for Calculating Ionic Equilibria in Milk as a Function of pH: Comparison to Experiment

Acidification is fundamental for the processing of milk into cheeses, caseins, and fermented dairy products. It is established that a pH decrease changes the ionic equilibria of milk, inducing the solubilization of micellar calcium phosphate. This study aimed to present a theoretical model calculating ionic equilibria in milk as a function of pH. From the pH and total concentrations of minerals and caseins, the model calculated the concentrations of all ionic species and their partition between micellar and aqueous phases of milk. As the pH decreased, the minerals present in the micellar phase were gradually displaced into the aqueous phase. The calculated concentrations of minerals were in a good agreement with the experimental ones determined from acidified milk. A very satisfactory accuracy of the calculations, estimated by a root-mean-square error (RMSE) value of 5% for Ca and P(i) and a slope of the plot close to a unit, was obtained. The model is proposed for the simulation of ionic equilibria and the partition of salts between the aqueous and micellar phases of milk and dairy formulations during acidification.

Secretion of Organic Acids by Phosphate Solubilizing Bacteria

Phosphorus availability is a major limiting for crop production. Bacterial solubilization of insoluble inorganic phosphate has been studied as a means of providing available phosphorus for crop production. Bacterial abilities to solubilize calcium phosphate and rock phosphate have been identified to be related with their abilities to produce gluconic acid and ketogluconic acid. However, there is no information regarding the relationship between bacterial ability to solubilize aluminum phosphate and their ability to produce organic acids. This study was conducted to investigate the relationship between bacterial ability to solubilize calcium and aluminum phosphates with their ability to produce organic acids. Bacterial ability to solubilize calcium and aluminum phosphates were determined as the concentration of soluble phosphate in the filtrate of bacterial cultivation media, while bacterial ability to produce organic acids were assessed from the accumulated organic acids in its. The results showed that bacterial abilities to solubilize calcium and aluminum phosphates well related to their abilities to produce organic acids. Organic acids related with the solubilization of calcium phosphate differ from the ones relatedAlam, S., S. Khalil, N. Ayub, and M. Rashid. 2002. In vitro solubilization of inorganic phosphate by phosphate solubilizing microorganisms (PSM) from maize rhizosphere. Int. J. Agri. Biol. 4: 454-458.Beauchemin, S., D. Hesterberg, J. Chou, M. Beauchemin, R.R. Simard, and D.E. Sayers. 2003. Speciation of phosphorus in phosphorus-enriched agricultural soils using X-ray absorption near-edge structure spectroscopy and chemical fractionation. J. Environ. Qual. 32:1809–1819.Bolan, N.S., R. Naidu, S. Mahimairaja, dan S. Baskaran. 1994. Influence of low-molecular-weight organic acids on the solubilization of phosphates. Biol. Fertil. Soils 18: 311-319.Cline, G.R., P.E. Powell, P.J. Szaniszlo, dan C.P. Reid. 1983. Comparison of the abilities of hydroxamic and other natural organic acids to chelate iron and other ions in soil. Soil Sci. 136: 145-157.Curtin, D., and J.K. Syers, 2001. Lime-induced changes in indices of soil phosphate availability. Soil Sci. Soc. Am. J. 65:147–152.Fox, T.R., N.B. Comerford, dan W.W. McFee. 1990. Phosphorus and aluminium release from a spodic Horizon mediated by organic acids. Soil Sci. Soc. Am. J. 54: 1763-1767.Hue, N.V., G.R. Craddock, dan F. Adams. 1986. Effect of organic acids on aluminium toxicity in subsoils. Soil Sci. Soc. Am. J. 50: 28-34.Johnson, S.E., and R.H. Loeppert. 2006. Role of organic acids in phosphate mobilization from iron oxide. Soil Sci. Soc. Am. J. 70:222–234.Kumari, A., K.K. Kapoor, B.S. Kundu, and R.K. Mehta. 2008. Identification of organic acids produced during rice straw decomposition and their role in rock phosphate solubilization. Plant Soil Environ. 54: 72–77Lopez-Hernandez, D., D. Flores, G. Siegert, dan J.V. Rodriguez. 1979. The effect of some organic anions on phosphate removal from acid and calcareous soils. Soil Sci. 128: 321-326.Lopez-Pineiro, A., dan A. Garcia-Navarro. 2001. Phosphate fractions and availability in Vertisols of South-Western Spain. Soil Sci. 166: 548-556.Olsen, S.R. dan Sommers, L.E. 1982. Phosphorus. In Page, A.L., Miller, R.H. &amp; Keeney, D.R. (eds.). Methods of Soil Analysis. Part 2. 2nd ed. ASA and SSSA Publisher, Madison.Rao, W.V.B.S., and M.K. Sinha. 1963. Phosphate dissolving microorganisms in the soil and rhizosphere. Indian J. agric. Sci. 33: 272-278.Rodriguez, H., T. Gonzalez, I. Goire, dan Y. Bashan. 2004. Gluconic acid production and phosphate solubilization by the plant growth-promoting bacterium Azospirillum spp. Naturwissenschaften 91: 552-555.Sagoe, C.I., T. Ando, K. Kouno, and T. Nagaoka. 1997. Effect of organic-acid treatment of phosphate rocks on the phosphorus availability to Italian ryegrass. Soil Sci. Plant Nutr. 43: 1067-1072.Sanchez, P.A. 1976. Properties and Management of Soils in the Tropics. John Wiley &amp; Sons, Inc. New York. 618 pp.Siddique, M.T., and J.S. Robinson. 2003. Phosphorus sorption and availability in soils amended with animal manures and sewage sludge. J. Environ. Qual. 32:1114–1121.Song, O.R., S.J. Lee, Y.S. Lee, S.C. Lee, K.K. Kim, dan Y.L. Choi. 2008. Solubilization of insoluble inorganic phosphate by Burkholderia cepacia DA23 isolated from cultivated soil. Braz. J. Microbiol. 39: 151-156.Sridevi, M., K.V. Mallaiah, and N.C.S. Yadav. 2007. Phosphate solubilization by Rhizobium isolates from Crotalaria species. J. Plant Sci. 2: 635-639.Traina, S.J., G. Sposito, D. Hesterberg, dan U. Kafkafi. 1986. Effects of pH and organic acids on orthophosphate solubility in an acidic, montmorillonitic soil. Soil Sci. Am. J. 50: 45-52.Trivedi, P., and T. Sa. 2008. Pseudomonas corrugata (NRRL B-30409) mutants increased phosphate solubilization, organic acid production, and plant growth at lower temperatures. Curr. Microbiol. 56: 140-144.Tunesi, S., V. Poggi, and C. Gessa. 1999. Phosphate adsorption and precipitation in calcareous soils: The role of calcium ions in solution and carbonate minerals. Nutr. Cycling Agroecosyst. 53:219–227.Zhang, M., A.K. Alva, Y.C. Li, dan D.V. Calvert. 2001. Aluminium and iron fractions affecting phosphorus solubility and reactions in selected sandy soils. Soil Sci. 166: 940-948.with the solubilization of aluminum phosphate. Moreover, there is similarity in the production of organic acids related to the solubilization of aluminum phosphates and iron phosphate.

Effect of milk solids concentration on the pH, soluble calcium and soluble phosphate levels of milk during heating

When milk is processed to dairy products, the concentration of the milk and the temperature/time combinations to which the milk is exposed can be varied. For example, large differences in milk concentrations and temperature/time combinations are used in the manufacture of milk powder or the various concentrated liquid milk products. Although the milk salts, particularly the concentrations and equilibrium states of calcium and inorganic phosphate, are considered to be important in the stability and functionality of dairy products, there have been few studies on the mineral balance in concentrated milk systems and how this is affected by temperature changes. The objective of this study was to examine the effect of milk concentration (9.6–38.4% w/w total solids), temperature (20–80 °C) and time (0–60 min) on the pH and the concentrations of soluble calcium (Casol) and soluble inorganic phosphate (Psol). At any given temperature, the level of Casol and Psol, as mmol·kg−1, increased and the pH decreased as the milk concentration was increased. However, when measured as a percentage of the total, the level of Casol and Psol decreased as the milk concentration was increased. At any given milk concentration, the level of Casol, Psol and milk pH decreased within the first few minutes of heating, with little further change at longer heating times. For milk samples at each concentration, there was a strong correlation between the final Casol and the final Psol at all temperatures. At any particular milk concentration, there was a strong correlation between the final milk pH and the final Casol or the final Psol levels. These results indicate that substantial decreases in milk pH, Casol and Psol can occur at the temperatures milk will experience in common commercial processes, and the extent of the changes will be dependent on the milk concentration and the processing conditions.

Stability of milk-derived calcium phosphate suspensions

Milk-derived calcium phosphate (MDCP) can be isolated from whey derived from acid casein or cottage cheese manufacture as a precipitated calcium phosphate material. However, the composition and suspension properties of this MDCP material are poorly understood. This study was aimed at examining the properties of MDCP when in suspension, and the factors affecting the stability of this calcium phosphate suspension. When suspended in water, MDCP aggregated, with the aggregation rate increasing with increasing temperature. Aggregation was more rapid in milk permeate than in water. The aggregation of MDCP increased with increasing ionic strength, and, as this was accompanied by a decrease in the magnitude of the ζ-potential, this could be explained by the effects of the electrolyte concentrations on the electrical double layers of the particles. Soluble calcium markedly increased the rate of aggregation of the MDCP, whereas soluble phosphate slightly retarded the aggregation. Soluble calcium changed the ζ-potential from negative to positive, with the particles becoming progressively more positive at higher soluble calcium levels. In contrast, increasing soluble phosphate levels made the ζ-potential of MDCP particles markedly more negative. These results indicate that the addition of soluble calcium or soluble phosphate had more specific effects, probably binding to the surface of the MDCP particles. The increased rate of aggregation in soluble calcium solutions could not be solely explained by the changes to the ζ-potentials of the particles.

A model for predicting salt equilibria in milk and mineral-enriched milks

The aim of this work was to present an original model predicting salt equilibria between the micellar and aqueous phases in milk and mineral-enriched milks. Calculations were based on interactions between cations (calcium, magnesium, sodium, potassium) and anions (citrate, chloride, inorganic phosphate and total caseins) according to their reciprocal affinity and considering pH, ionic strength, and solubility of calcium phosphate. In order to validate the model, the theoretical salt equilibria in milk and milks enriched with different salts (CaCl2, NaCl, phosphate and citrate) at pH 6.75 were compared with experimental results published in the literature. Comparison of simulated results to known values reported in the literature showed a good agreement. In conclusion, this model constitutes an interesting tool for simulating salt equilibria in milk in order to prepare various dairy formulations with different concentrations of minerals and caseins.

Calcium Phosphate Solubility: The Need for Re-Evaluation

The determination of the solubility of calcium phosphates by the conventional large excess of solid method has been demonstrated to be inappropriate. The problem lies in incongruent dissolution, leading to phase transformations, and lack of detailed solution equilibria: all calculations have been based on simplifications, which are only crudely approximate. The absolute solid-titration approach shows excellent reliability and reproducibility. Using solid titration, the true solubility isotherm of hydroxyapatite (HAp) has been found to lie substantially lower than previously reported. In addition, contrary to wide belief, dicalcium phosphate dihydrate (DCPD) is not the most stable phase below pH ∼4.2, where calcium-deficient HAp is less soluble. The misunderstanding here arises from the metastability of DCPD, which nucleates much more easily than HAp at low pH. Such results indicate that the Ca−P system is in need of complete reappraisal. The solid-titration method can be extended to other complex systems.