Impact of heat moisture treatment and hydration level on physico-chemical and viscoelastic properties of doughs from wheat-barley composite flours

摘要

The impact of heat moisture treatment (HMT) on the thermoviscous, viscoelastic and mechanical properties of binary flour matrices (wheat:barley, 60:40, wt:wt) was investigated in untreated and HMT (15% moisture content, 1 h heating time at 120 °C) hydrated samples to assess the potential of HMT to modify dough viscoelasticity and doughmaking functionality in diluted breadmaking wheat matrices. HMT significance was tackled (a) in excess of water, by applying successive cooking and cooling cycles to hydrated samples (14%, w:w), determination of viscometric parameters, and subsequent determination of textural (compression test) and viscoelastic parameters (stress relaxation test) in pasted and gelled hydrated flours, and (b) under water restrictions by assessing the consistency (forward extrusion test), the primary and secondary mechanical properties (Texture Profile Analysis), and the viscoelastic behaviour (stress relaxation test) of untreated and HMT mixed doughs made at different flour hydration levels (63 and 70%). In highly hydrated blends, HMT barley flour provided enhanced viscosity patterns regardless of the presence of native or HMT wheat flour, and harder gels with larger initial stress to reach a defined deformation, particularly in the presence of HMT wheat flour. Under restricted water availability, doughs made at 70% hydration level when compared to their counterparts made at 63% explicited lower stress relaxation curves with higher values for both initial decay rate and extent of the decay, shorter relaxation times and higher percent of stress relaxation, giving softer and more cohesive doughs. The most elastic-like dough blends were those prepared with HMT wheat and barley flours at 63% hydration, while the most viscous-like doughs were those from native flours made at 70% hydration.