Dough aeration and rheology: Part 3. Effect of the presence of gas bubbles in bread dough on measured bulk rheology and work input rate

The effects of dough aeration on measured bulk rheology of dough were investigated by
preparing doughs with various gas contents and assessing their rheology under large deformation biaxial extension using the SMS Dough Inflation System. Doughs were mixed to various gas contents using a laboratory-scale mixer, the Tweedy 1, at various mixer headspace pressures. In order to consider the effect of oxidation processes, doughs were mixed in air, in nitrogen and in a controlled oxygen-nitrogen atmosphere in which the partial pressure of oxygen was kept constant. In the latter two cases a flow rate of gas through the mixer was maintained, while the doughs mixed in air had a static headspace. Dough
aeration was quantified using density measurements. The dough rheology tests were performed under two different modes: constant volumetric air flow rate; and constant strain rate at two levels, 0.1 and 0.05 s−1.
Analysis of the stress–strain data of an inflating dough bubble using an exponential model enabled the strain hardening index, failure strain and failure stress to be determined. The strain hardening index, failure strain and failure stress decreased with gas content, indicating that gas bubbles in dough disrupt
the integrity of dough structure. The faster strain rate tended to give higher values of all parameters and to be more discriminating, while testing at a constant volumetric air flow rate gave lower values. Doughs mixed under a constant partial pressure of oxygen resulted in the strain hardening index being minimally affected by the gas content, although failure strain and failure stress decreased with increasing gas content
in the dough. The flow of gas through the mixer appeared to affect dough aeration and rheology, and the rate of work input was found to increase with increasing mixer headspace pressures. These suggest that dough aeration not only affects the rheology of static dough through the physical presence of gas bubbles following mixing, it also affects the development of its rheological properties within the mixer, through the physical presence of the bubbles affecting the rate of work input that develops the doughs, and also
through the turnover of air that supplies oxygen to facilitate this development.