Structure factor and elasticity of a heat-set globular protein gel

Cross-correlation dynamic light scattering was used to measure the structure factor of heated solutions of the globular protein beta-lactoglobulin at pH 7 and 0.1 M NaCl. After 24 h heating at 80 degreesC finite size aggregates are formed at protein concentrations below 15 g/L, whereas at higher concentrations turbid gels are formed. The gels may be considered as collections of randomly close packed "blobs" with a self-similar structure characterized by a fractal dimension d(f) = 2.0 +/- 0.1. The concentration dependence of the structure factor was compared with that of the elastic shear modulus. The results for this particular protein system were consistent with predictions of the so-called fractal gel model. Limits of validity of the model are discussed.