Effect of calcium on ovine caseinate functional properties

Abstract

The solubility of colloidal particles of ovine caseinate in the presence of calcium was followed by analyzing the colloidal particle size and the protein composition of colloidal particles remaining in suspension. A comparison between the behavior of bovine and ovine caseinate was carried out. A sequential two-step salting-out process, due to progressive Ca2+ binding to at least two kinds of sites, was observed for both caseinates. The precipitation curves were fitted, and the affinity constants and binding site numbers were calculated with an equation based on the concept of Wyman's linked functions. Ovine caseinate colloidal aggregates obtained in the presence of calcium turned out to be less stable and bigger than the bovine ones. Calcium binding to protein residues modifies the composition and the conformation of caseinates. An aggregation process at low ovine caseinate concentrations and a gelation process at high protein concentrations induced by glucono-lactone hydrolysis were studied in the presence of calcium concentrations where no precipitation is observed. The presence of calcium affects the kinetics of both processes and the final state of aggregates and gels network formed. The degree of compactness, average size of the aggregates, and rheological properties of gels formed at the end of the acidification process depend on the calcium concentration added.