Dynamic Viscoelastic and Tensile Properties of Gluten and Glutenin Gels of Common Wheats of Different Strength

Abstract

Dynamic viscoelastic properties at 25 °C of gluten and glutenin gels were obtained from Canadian common wheats of different strengths. The relaxation spectra showed a maximum intensity at a characteristic relaxation time (τ*). The relaxation modulus associated with this maximum was taken as the strength of the glutenin or gluten gel transient network (G(τ*)). The ratio of G(τ*) for glutenin and gluten gels from the same cultivar ranged from 5.6 for an extra strong cultivar to 51.1 for a soft wheat. This gives indirect evidence that the gliadin fraction weakens the glutenin gel network more in weaker cultivars. In addition, the fact that both glutenin and gluten gels showed extensive stress relaxation coupled with the fact that addition of l-cysteine to a gluten gel eliminated the network structure at 25 °C and resulted in a power law stress relaxation spectrum suggests that the transient network in gluten is a reversible network. This power law relaxation pattern was not seen here for an entangled polymer melt (poly(dimethylsiloxane)). It was also found here that the viscosity of the gluten gel (G(τ*) × τ*) trended best with the tensile stress build-up in a uniaxial tensile test of gluten gels. Together, these results indicate that both network strength and relaxation times should be considered in characterizing the linear viscoelastic properties of hydrated cereal proteins. Keywords: Gluten; glutenin; reversible gels; rheology; stress relaxation; viscoelastic properties; tensile properties