Calcium-induced aggregation of bovine caseins : effect of phosphate and citrate

• Published in: Colloid and polymer science Vol. 285; no. 5; pp. 507 - 514
• Main Authors: ALVAREZ, Estela M, RISSO, Patricia H, GATTI, Caries A, BURGOS, Mariano, SALA, Virginia Suarez
• Format: Journal Article
• Language: English
• Published: Berlin Springer 01-02-2007; Springer Nature B.V
• Subjects: Agglomeration; Applied sciences; Binding sites; Biological and medical sciences; Calcium; Casein; Colloids; Concentration (composition); Exact sciences and technology; Fundamental and applied biological sciences. Psychology; In solution. Condensed state. Thin layers; Mathematical analysis; Molecular biophysics; Natural polymers; Phosphates; Physico-chemical properties of biomolecules; Physicochemistry of polymers; Precipitates; Precipitation; Proteins; Phosphates; Chemical precipitation; Citrate; Experimental study; Mechanism; Caseins solubility; Calcium ion; Casein; Medium effect; Phosphate; Animal protein; Molecular aggregation; Aqueous solution; Calcium precipitation; Saline solution; Colloid particle
• ISSN: 0303-402X; 1435-1536
• DOI: 10.1007/s00396-006-1588-2

The formation of colloidal particles by Ca2+ precipitation of whole caseinates in the presence of phosphate (Pi), citrate (Cit), or both of the anions in concentrations found to be effective in previous works was followed comparing the colloidal particle size and the ionic and proteic composition of the precipitates obtained. Ca2+ was incorporated to the precipitate and colloidal particles in a different way than Pi, differences which were related to the presence of Pi and/or Cit in the media. A sequential salting-out process due to progressive Ca2+ binding to at least two kinds of sites was observed. The precipitation curves were fitted, and the affinity constants and binding site numbers were calculated with a modification of the Farrell's equation based on the concept of Wyman's linked functions. Precipitates obtained at low total Ca2+ concentrations in different conditions varied their casein composition. Colloidal particles appeared at the beginning of the second salting-out step, in different amount, and in average size according to the presence or absence of Pi and/or Cit in the media. Consideration of these differences showed that Cit favored the formation of bigger colloidal particles, acting especially in the first steps of the casein aggregation and conditioning the mechanism of this process.