title: Effects of citrate and NaCl on size, morphology, crystallinity and microstructure of calcium phosphates obtained from aqueous solutions at acidic or near-neutral pH.
abstract: Precipitation of calcium phosphates occurs in dairy products and depending on pH and ionic environment, several salts with different crystallinity can form. The present study aimed to investigate the effects of NaCl and citrate on the characteristics of precipitates obtained from model solutions of calcium phosphate at pH 6·70 maintained constant or left to drift. The ion speciation calculations showed that all the starting solutions were supersaturated with respect to dicalcium phosphate dihydrate (DCPD), octacalcium phosphate (OCP) and hydroxyapatite (HAP) in the order HAP>OCP>DCPD. X-ray diffraction (XRD) and Fourier transform infrared (FTIR) analyses of the precipitates showed that DCPD was formed at drifting pH (acidic final pH) whereas poor crystallised calcium deficient apatite was mainly formed at constant pH (6·70). Laser light scattering measurements and electron microscopy observations showed that citrate had a pronounced inhibitory effect on the crystallisation of calcium phosphates both at drifting and constant pH. This resulted in the decrease of the particle sizes and the modification of the morphology and the microstructure of the precipitates. The inhibitory effect of citrate mainly acted by the adsorption of the citrate molecules onto the surfaces of newly formed nuclei of calcium phosphate, thereby changing the morphology of the growing particles. These findings are relevant for the understanding of calcium phosphate precipitation from dairy byproducts that contain large amounts of NaCl and citrate.
authors.affiliation: INRA/Agrocampus Ouest, UMR1253 Science et Technologie du Lait et de l'Oeuf, 65 rue de Saint Brieuc, F-35042 Rennes, France.
authors.forename: Omar
authors.initials: O
authors.lastname: Mekmene
authors.forename: Thierry
authors.initials: T
authors.lastname: Rouillon
authors.forename: Sophie
authors.initials: S
authors.lastname: Quillard
authors.forename: Paul
authors.initials: P
authors.lastname: Pilet
authors.forename: Jean-Michel
authors.initials: JM
authors.lastname: Bouler
authors.forename: Stéphane
authors.initials: S
authors.lastname: Pezennec
authors.forename: Frédéric
authors.initials: F
authors.lastname: Gaucheron
mesh_terms: D002130:Calcium Phosphates / Q000737:chemistry*; D011232:Chemical Precipitation; D019343:Citric Acid / Q000494:pharmacology*; D003460:Crystallization; D017886:Durapatite / Q000737:chemistry; D006863:Hydrogen-Ion Concentration; D008854:Microscopy, Electron; D010316:Particle Size; D012965:Sodium Chloride / Q000494:pharmacology*; D012996:Solutions; D017550:Spectroscopy, Fourier Transform Infrared; D014867:Water; D014961:X-Ray Diffraction
chemical_list: D002130:Calcium Phosphates; D012996:Solutions; D014867:Water; D019343:Citric Acid; D012965:Sodium Chloride; D017886:Durapatite; C020243:calcium phosphate