Scaling and fractal analysis of viscoelastic properties of heat-induced protein gels

The scaling of viscoelastic properties of heat-induced gels prepared from egg white was investigated at five pH values (pH 3–11) and various protein concentrations (5–20%) using small-deformation oscillatory rheological measurements. Protein gels were formed by heating samples at 80 °C for 1 h followed by cooling to 25 °C. Storage modulus, G′ and critical strain, γ0 of the gels exhibited pH-dependent power-law relationships with protein concentration. Based on the power-law exponent values, fractal dimension, df of heat-induced protein gels was estimated using scaling models from the literature. Low df values (1.9–2.1) were obtained for gels prepared at acidic and neutral pHs (3–7) whereas higher df values (2.2–2.4) were obtained for gels formed under basic pH conditions. These df values lied well within the range of fractal dimension values (1.5–2.8) reported for protein gels. However, they slightly differed from df for diffusion-limited and reaction-limited cluster–cluster aggregation processes, which made it difficult to justify an assumption regarding the nature of the aggregation process of these protein systems.