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

The effect of the NaCl concentration ( C s ) on the structure factor and the turbidity of heat-set β-lactoglobulin gels and aggregates was investigated using light and X-ray scattering. Cross-correlation dynamic light scattering was applied to correct for multiple scattering in turbid systems. For C s ≤ 50 mM the gels are transparent and homogeneous on length scales above 20 nm, showing interaction peaks in small-angle X-ray scattering. For C s ≥ 200 mM the gels are opaque and heterogeneous on the micron length scale as shown by confocal scanning light microscopy. At intermediate salt concentrations the gels are characterized by a correlation length beyond which they are homogeneous, which decreases with increasing protein concentration and decreasing salt concentration. The fractal structure at smaller length scales is identical to that of the aggregates formed in dilute solution.