Shear softening and thixotropic properties of wheat flour doughs in dynamic testing at high shear strain

Abstract

Shear softening and thixotropic properties of wheat flour doughs are demonstrated in dynamic testing with a constant stress rheometer. This behaviour appears beyond the strictly linear domain (strain amplitude γ0 ≥ 0.2%),G′,G″ and |η*| decreasing with γ0, the strain response to a sine stress wave yet retaining a sinusoidal shape. It is also shown thatG′ recovers progressively in function of rest time. In this domain, as well as in the strictly linear domain, the Cox-Merz rule did not apply butη(γ) and |η*(ω))| may be superimposed by using a shift factor, its value decreasing in the former domain when γ0 increases. Beyond a strain amplitude of about 10–20%, the strain response is progressively distorted and the shear softening effects become irreversible following rest.