The pH Dependence on the Rheology of Wheat Protein Isolate Suspensions

Abstract

Linear and non-linear rheological properties of wheat protein isolate (WPI) suspensions were investigated as a function of concentration and pH. Linear dynamic viscoelastic properties for WPI were strongly dependent on concentration and pH. The higher the concentration, the stronger the viscoelasticity of the WPI would be. In the pH range of 4.0-7.0, higher pH resulted in stronger viscoelasticity. WPI suspensions exhibited viscoelastic fluid behavior at lower concentration and/or lower pH. However, at high concentration and high pH, WPI suspensions showed some transition from viscoelastic fluid into viscoelastic solid, and displayed viscoelastic solid behavior at low frequencies. Concentration and pH ranges for the transition were narrow indicating that the property change for the WPI was in evidence. The non-linear shear viscoelastic properties of WPI were also found to depend on concentration and pH. Viscosities of WPI displayed shear-thinning behavior, and fits by a power law constitutive model. Our results indicate that the WPI structure in suspension changes over a small concentration and pH range, which suggest that WPI could be important for adjusting and controlling dough viscoelastic behavior. The information of this work is useful in the development of more and new applications using wheat protein isolate.