Rheological Behavior of High-Concentration Sodium Caseinate Dispersions

Apparent viscosity and frequency sweep (G', G '') data for sodium caseinate dispersions with concentrations of approximately 18% to 40% w/w were obtained at 20 degrees C; colloidal glass behavior was exhibited by dispersions with concentration >= 23% w/w. The high concentrations were obtained by mixing frozen powdered buffer with sodium caseinate in boiling liquid nitrogen, and allowing the mixtures to thaw and hydrate at 4 degrees C. The low-temperature G' - G '' crossover seen in temperature scans between 60 and 5 degrees C was thought to indicate gelation. Temperature scans from 5 to 90 degrees C revealed gradual decrease in G' followed by plateau values. In contrast, G '' decreased gradually and did not reach plateau values. Increase in hydrophobicity of the sodium caseinate or a decrease in the effective volume fraction of its aggregates may have contributed to these phenomena. The gelation and end of softening temperatures of the dispersions increased with the concentration of sodium caseinate. From an Eldridge-Ferry plot, the enthalpy of softening was estimated to be 29.6 kJ mol(-1). Practical Application: The results of this study should be useful for creating new products with high concentrations of sodium caseinate.