Structure of heat-induced plasma protein gels studied by fractal and lacunarity analysis

Fractal and lacunarity analysis were used to examine the structure of heat-induced gels of plasma proteins at pH 5.0, 6.0 and 7.0. A scaling model based on rheological measurements was used to calculate the fractal dimension (Df), which was comprised between 2.63 and 2.70. Scanning electron microscopy was used to determine Df by the box count method. In this case, Df ranged from 2.78 to 2.83. All Df values corresponded to gels with high degree of scale invariance. Also, a weak-link behaviour was determined. The fact that decreasing pH entailed a slight decrease in Df could be ascribed to the growth of larger aggregates due to the reduction of electrostatic repulsion. Lacunarity measures complemented fractal analysis by describing the distribution of the cavities within the gel network. It was found that the heterogeneity of cavities distribution pattern increased as pH decreased. This feature could be related to macroscopic properties such as water holding capacity.