Effects of Mixing and Large-Amplitude Oscillatory Shear Deformations on Microstructural Properties of Gliadin and Glutenin as Captured by Stop-Flow Frequency Sweeps in Small-Amplitude Oscillatory Shear

Gliadin and glutenin extracted from vital wheat gluten were studied using Large Amplitude Oscillatory Shear (LAOS) followed by stop-flow frequency sweep tests after being subjected to short (4 min) and prolonged (60 min) mixing times. The LAOS tests were conducted at up to two different strain amplitudes (γ: 0.1%, 200%; <i>ω</i>: 10 rad/s) to apply small and large deformations to the gliadin and glutenin after mixing for different time periods. Frequency sweep tests (<i>ω</i>: 0.01-100 rad/s, γ: 0.06%) revealed an increase in the elasticity of gliadin with respect to an increasing mixing time, as evidenced by a robust increase in G'(<i>ω</i>), coupled with a less robust increase in G″(<i>ω</i>). Consistent with the increase in elasticity, a progressively lower tanδ(<i>ω</i>) and G'(<i>ω</i>) slope were observed for the gliadin that underwent 60 min of mixing followed by large LAOS deformations. However, G'(<i>ω</i>), G″(<i>ω</i>), and η*(<i>ω</i>) remained constant for glutenin as the mixing time increased. Elastic decay with an increase in tanδ(ω) was found for glutenin when subjected to prolonged mixing followed by large LAOS deformations, which became apparent at high frequencies. The stop-flow LAOS (non-linear region)-frequency sweep (linear region) tests provided an understanding of how exposure to different mixing times and LAOS deformations of different magnitudes influence the mechanical/rheological properties of the main gluten proteins.