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The Bubble Size Distribution and Its Evolution in Wheat Flour Doughs Investigated by Synchrotron X-Ray Microtomography
F. KOKSEL (1), S. Aritan (2), A. Strybulevych (1), J. H. Page (1), M. G. Scanlon (3). (1) University of Manitoba, Winnipeg, MB, Canada; (2) Biomechanics Research Group, Faculty of Sports Sciences, Hacettepe University, Ankara, Turkey; (3) Department of Food Science, University of Manitoba, Winnipeg, MB, Canada

Understanding how the bubble size distributions are formed during mixing and controlling bubble nucleation are the basis for predicting and improving final product quality before bread is fully manufactured.  X-rays from a synchrotron source (Biomedical Imaging and Therapy beamline, Canadian Light Source) were used to rapidly characterize the initial bubble size distribution and its evolution in dough subsamples over the course of 3 hours following mixing.  A complete X-ray microtomography scan over 180° was completed within 120 s.  The number density of bubbles ranged from 600 to 2350 mm<sup>-3</sup>, which was higher than results previously reported.  The higher number density of bubbles was attributed to the better contrast, higher resolution, and thus smaller pixel size (8.75 μm) of the reconstructed X-ray images generated from synchrotron X-rays.  The bubble size distribution was very well characterized with a lognormal distribution function.  This distribution had a median bubble radius of 22.1 ± 0.7 μm at 36 minutes after the end of mixing which increased to 29.2 ± 0.2 μm over 190 minutes, a trend indicative of transport of gas in the dough due to disproportionation.  This is the first time disproportionation in nonyeasted wheat flour doughs has been monitored using X-rays from a synchrotron source.  These results imply that very small bubbles, which could not be observed in previous studies due to resolution limitations, are actually present in bread dough and their diffusion driven dynamics can be followed by synchrotron source X-rays after feature extraction using custom written image analysis software.

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