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The addition of yellow pea hull fibre to wheat bread supports the growing trend of improving health through diet. However, fibre addition tends to affect the structural and mechanical properties of dough, specifically through its destabilization of the developing gas bubble structure so that final bread volume and crumb texture are impaired. Understanding the mechanisms by which pea fibre detrimentally affects dough structure during proofing will improve our capacity to manage the factors that affect the design of fibre-enriched breads.  A broadband ultrasonic transducer was used in reflection mode to measure the properties of dough pieces as they proofed.  Two ultrasonic parameters that measure the rheology of dough (phase velocity and attenuation coefficient) were used to characterize changes in dough properties with time.  The objective was to determine how pea fibre particle size, fibre addition level, and optimization of water absorption affected changes in velocity and attenuation during dough proofing with a view to understanding fibre’s effect on gas cell development. For both the control and fibre-enriched doughs, attenuation increased while velocity decreased at the beginning of proofing, demonstrating substantial gas cell expansion.  The fibre-enriched dough also had broader peaks in velocity than the control, indicating the presence of smaller bubbles, likely due to a low degree of coalescence. Fibre-enriched doughs with optimized water absorption had ultrasonic patterns with proofing time that were more similar to the control dough than doughs with non-optimized water absorption.  Although improving contact between dough and transducer (especially at long proofing time) is necessary to improve reliability of the technique, ultrasonic measurements are a useful tool for optimizing pea fibre addition to bread.