Rheological Studies of Physical Soy Protein Gels

Many naturally-occuring gels exists in the biological systems such as foods. Because of their biodiversibily and delicate nature, their properties can be used by the food industry to achieve a variety of physicochemical functions. The gel utilized in this study, soy protein isolates (SPI) and concentrates (SPC), all have unique rheological properties which play an important role in their strength function of foods. The objective of this study is to gain insights as to how the rheological properties of these bio-gels are designed to control the gel-strength of these materials. The concentration dependence of dynamic moduli G’ and G” of soy protein isolates (SPI) and soy protein concentrates were studied in solutions prepared under different conditions. Three-level preliminary fractional experiments were undertaken to study effects of temperature, pH, and concentration on the gel-strength of these products. 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) and n*(ω) at the gel point. At low temperatures and high concentrations we get weaker 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 but points towards to becoming stronger gels.