Salt and Acid-Induced Soft Tofu-Type Gels: Rheology, Structure and Fractal Analysis of Viscoelastic Properties as a Function of Coagulant Concentration

The coagulant concentration dependence on the rheological properties of acid and salt- induced soft tofu-type gels formed with heated soy protein solutions was investigated. All gels showed a clear gel- like behavior, with acid- induced gels having the highest storage modulus (G'). Increase in coagulant concentration resulted in higher G' and shorter gelation time (t(gel)). The dependence of tgel on the coagulant concentration could be scaled with a power law model with R-2 varying between 0.9535 and 0.9787. Also the dynamic moduli change over angular frequency fitted well the models: G'(')similar to G(0)omega(n') and G''(')similar to G(0)(''omega n). The increase in shear deformation at fracture and shear stress yielding was directly proportional to the increase in coagulant concentration. Both gels were found in the transition regime with varying protein concentration, when experimental data were scaled with a fractal model. Salt- induced gels had more uniform network pore size, finer and smoother surface texture than acid- induced gels. Dynamic moduli analysis of the gels was significantly affected by coagulant type and concentration (p < 0.05).