Flour quality and disproportionation of bubbles in bread doughs

The bread making process transforms wheat flour doughs into highly porous breads. Bread has been shown (Wang, Austin and Bell, 2011) to be a single, open cell that is massively interconnected giving it a maze-like structure that encompasses the entire volume. The solid strands are also porous and contain closed cells. How the bubbles in dough mix partition into these open and closed cells in bread is not known. This study was undertaken to track changes in bubbles in doughs using 3-D X-ray microtomography techniques as doughs proofed and were baked. The mechanical properties of doughs were measured to establish how dough rheology impacted bubble growth. The doughs were made with 'medium strong' Canadian flour (CWRS) and 'weak' Australian flours (Wylk). Both doughs had similar protein amounts and strain-hardening characteristics; however the CWRS dough was more elastic. The scans identified formation of clusters of partially-coalesced bubbles from which one cluster grew to form a massively interconnected, single, closed cell in doughs as doughs proofed. Microscopy studies confirmed that the open cell in breads was made of partially-coalesced bubbles. Compared to the dough made with the Australian flours, the dough made from Canadian flour had a thicker dough layer separating bubbles, smaller size bubbles and a slower rate of formation of the continuous structure. This study highlights the critical role of dough elasticity and the disproportionation phenomena of bubble growth in controlling the quality of cell structures in dough and baked products.