Linear and Non-linear Rheology of Bread Doughs Made from Blends of Wheat (Triticum aestivum L.) and Rye (Secale cereale L.) Flour

Abstract

Strain hardening of wheat flour (WF) proteins during fermentation and baking is at the basis of the excellent quality of wheat breads. Yet, there are good reasons to use rye flour (RF), such as its high content of dietary fiber and other bioactives. However, rye proteins lack the ability to form dough with sufficient strain hardening capacity under extension, which partially explains the inferior quality of rye breads. A promising strategy to make high-quality breads with high nutritional value is the use of WF and RF blends. Despite this, the rheological behavior of WF/RF bread doughs has not yet been investigated. This study examines their rheology by non-linear uniaxial extensional and small-amplitude oscillatory shear measurements, and relates these measurements to the quality of the resulting breads. The strain hardening index (SHI), derived from extensional measurements, is expressed as the transient extensional viscosity at maximum strain [ηe+(εmax)] relative to the linear extensional viscosity extrapolated to maximum strain [ηe0+(εmax)]. Both the SHI and bread volume decreased when the level of RF in the blend increased. As an example, replacing 60% WF by RF led to a relative decrease of the SHI and bread volume of 34 and 64%, respectively. The decrease of the SHI is correlated to an increase in ηe0+(εmax). Comparison of the extensional curves of doughs made with blends of WF and RF and doughs made with blends of WF and wheat starch (WS) further revealed that RF components play a major role in the rheology of the doughs. In conclusion, it was found that WF/RF blends need to contain at least 60% WF to obtain bread of proper quality.