Comparison of Sequence of Physical Processes (SPP) and Fourier Transform Coupled with Chebyshev Polynomials (FTC) methods to Interpret Large Amplitude Oscillatory Shear (LAOS) Response of Viscoelastic Doughs and Viscous Pectin Solution

Abstract

Fourier Transform coupled with Chebyshev Polynomials (FTC) and Sequence of Physical Processes (SPP) are used to study and interpret the large amplitude oscillatory shear (LAOS) responses of doughs. The doughs were prepared with semolina, hard, soft wheat flours, and a pectin solution was studied as a highly viscous reference. The FTC method enables the extraction of user-friendly measures at limiting conditions (γ→0, γ→ γmax) including (GL′,GM′,GL″,GM″). The SPP method provides instantaneous storage (Gt′) and loss (Gt″) moduli, results in a complete deformation history throughout the oscillation cycle. Rheological characteristics obtained using SPP measures offer a better correlation with protein content, LMW/HMW ratio, and glutenin/gliadin ratio of the flour doughs. Instantaneous moduli (Gt′,Gt″) determined by the SPP method are more sensitive to structural changes than FTC measures for detecting network rupture at lower strain amplitudes. The FTC results show that the nonlinear behavior of dough is characterized by intracycle strain-hardening (GL′ >GM′) and intracycle shear-thinning (GL″ <GM″). The SPP method shows that the doughs undergo a 3-step gradual sequence of physical processes governed by starch/gluten interactions. These steps include: (1) weak strain-hardening and strong-shear thickening due to the elongation of the gluten network and formation of starch hydro-clusters, (2) strong strain-softening, and shear-thickening behavior caused by the relaxation of the gluten network and sustained formation of starch hydro-clusters, (3) weak strain-hardening and strong shear-thinning due to reassembly of the gluten network and the degradation of starch hydro-clusters. Although the FTC method provides user-friendly and easy-to-interpret measures, the time-related information extracted by the SPP method provides a more detailed history of microstructural changes during an oscillation cycle.