Specific effect of calcium ions on thermal gelation of aqueous micellar casein suspensions

Abstract Aqueous suspensions of micellar casein (MC) gel when heated above a critical temperature that depends on the pH. The effect of adding CaCl 2 and EDTA on thermal gelation was studied in order to assess the effect of increasing or decreasing the amount of bound Ca 2+ on the process. The effect of adding NaCl was investigated in order to distinguish the effect of Ca 2+ binding from the effect of screening of electrostatic interactions. Shear moduli were measured as a function of the temperature during heating ramps up to 90 °C. Gel formation was characterized by a sharp increase of the storage modulus at a critical temperature (T c ). In most cases, prolonged heating at 90 °C did not cause a significant increase of the gel stiffness. Addition of CaCl 2 caused a decrease of T c , whereas addition of NaCl caused an increase of T c . Chelation of Ca 2+ by EDTA led to a strong increase of T c even if the fraction of chelated Ca 2+ was small and the micelles remained intact. The gel stiffness was found to increase weakly with increasing CaCl 2 concentration up to 20 mM. The gels persisted during cooling to 20 °C with an increase of the elastic modulus by a factor between 4 and 6 depending on the CaCl 2 concentration. The results demonstrate that Ca 2+ plays a crucial role in thermal MC gelation.