Effect of leavening time on LAOS properties of yeasted wheat dough

Abstract

Wheat dough is subjected to large deformations under realistic processing conditions. The viscoelasticity under large deformations can be hardly captured by traditional small amplitude oscillatory tests. Large amplitude oscillatory shear (LAOS) tests are required for accurate characterization of the nonlinear mechanical response. In this regard, LAOS studies of yeasted wheat dough leavened at different times (0, 30, 60, 90 and 120 min) were carried out in this work, in the strain range from 0.1% to 100% (frequency 2π rad/s). All the dough samples showed a complex rheological response that was characterized by strain stiffening and shear thinning behavior at large strains. FTIR analysis revealed that starch granules were increasingly hydrated and protein molecular configuration was modified by the yeast activity. It was postulated that modifications of the protein secondary structure can be behind the strain stiffening behavior while the suspended starch matrix was associated with the shear thinning behavior. LAOS enabled to disaggregate the viscoelasticity of the wheat dough to assess the nonlinear effects associated with elasticity and energy dissipation mechanisms. Overall, a longer leavening time increased by about 30% the nonlinear mechanical response of wheat dough, an effect probably induced by variations in the secondary structure of wheat proteins and to the gassing of the dough microstructure as consequence of the yeast metabolic activity. The results in this work showed that LAOS is a suitable method for characterization of the nonlinear mechanical response of whet dough, especially for assessing the effect of processing conditions (e.g., leavening time and yeast content).