Influence of the Ionic Strength on the Structure of Heat-Set Globular Protein Gels at pH 7. Ovalbumin

Abstract

The effect of the NaCl concentration (Cs) on the structure factor and the turbidity of heated ovalbumin solutions was investigated using cross-correlation dynamic light scattering. The heated systems are characterized by a correlation length, which depends on protein and salt concentration, beyond which they are homogeneous. At length scales below this correlation length, the systems have a self-similar, fractal, structure. For Cs ≥ 100 mM, very turbid systems are formed with correlation lengths that show strong concentration dependence, and the correlation length rapidly rises above 1 μm at protein concentrations above 4 g/L. For Cs ≤ 30 mM NaCl the systems remain transparent with relatively small correlation lengths (<20 nm). At 50 mM NaCl the correlation length first increases strongly with increasing protein concentration followed by a decrease above 8 g/L. At both 30 and 50 mM, an unexpected increase in the correlation length and turbidity is observed at high protein concentrations (above 40 and 30 g/L, respectively). From the present work we conclude that the structure of heated globular protein solutions and gels is generally determined by the interplay between the growth of the aggregates and the electrostatic interaction between the aggregates.