Rheological Properties of a Soy Protein Isolate and Concentrate: Effect of Gel Strength

The concentration dependence of dynamic moduli G’ and G” of soy protein isolates (SPI) and soy protein concentrates (SPC) were studied in solutions prepared under different conditions. Three-level preliminary fractional experiments were undertaken to study effects of temperature, pH, concentration on the gel strength of soy protein isolate and soy protein concentrate solutions. Protein concentration, pH and temperature appear to have an impact on the strength of these bio-gels. An investigation of the viscoelastic behavior of SPI solution at the sol-gel transition point was mainly considered by applying a rheological testing procedure. The data demonstrated a power law frequency dependence of the viscoelastic functions G ́(ω), G”(ω) and n*(ω) at the gel point. At low temperatures and high concentrations we get stronger gel-strengths than at high temperatures and low concentrations. Lowering the concentration and keeping the temperature constant seem to have little effect on the gel strength.