Hydrodynamic properties–structure relationship for sodium caseinates in presence of calcium

Structural modifications of sodium caseinates (Na-CAS) were produced by a gradual addition of Ca2+ to Na-CAS solutions. Measurements of the limiting viscosity number of such solutions and the specific volume of the aggregates formed showed the production of conformational changes leading to progressively less flexible structures.Measurements of fluorescence spectra of calcium caseinates (Ca-CAS) mixtures at increasing Ca2+ concentrations and high Ca2+/CAS mass concentration ratios showed an increase in the fluorescence intensity and a blue shift of the fluorescence band that could be the result of the insertion of Trp residues in more hydrophobic environments able to protect them better from the solvent quenching. A similar behaviour was observed for the near-UV CD spectra, which also showed an increase in the ellipticity and a red shift for the Trp and Tyr bands. These results were consistent with the production of more compact structures by action of the Ca2+, in which the aromatic residues were buried.