Confocal microscopy of bread dough under controlled thermo-mechanical treatment

International audience

anglais. The rheology of bread dough is known to be complicated. However, it was extensively studied using both empirical and fundamental rheology characterizations. Many studies proposed correlations between rheological properties and macroscopic behavior such as elastic recovery after shaping or alveolar structure after proofing and cooking. The protein gluten network is recognizing to play a major role on the rheology of the dough. On the other hand, dough microstructure was observed at different scales using microscopy techniques such as CSLM. However, to our knowledge, no study exists on the direct observation of the evolution of the gluten organization at microscopic scale under shearing and heating. Using a home made rheo-optic device mounting on a confocal microscope, bread dough for different composition (water, sugar and oil contents) under continuous or oscillating strain was studied to find the optical signature of microstructure changes in relation with shear-thickening effect previously measured. This device allows controlling the strain and the shear rate but also the temperature of the dough, all parameters causing changes in gluten microstructure. It was shown that the higher the water content or the sugar content, the stiffer was the gluten strands but the less continuous the network before shearing and the more reinforced were the gluten strands under shearing. Moreover, the oil could be observed in the form of droplets located at the dough/bubble interface and in the form of gluten/oil co-localisation areas around the bubbles. Shearing the dough using an oscillatory strain signal leaded to an increase of the co-localisation areas. Finally, by a controlled increase of temperature, the growth of an air bubble in bread dough containing yeast was followed during proofing. The influence and the disposition of fat globules at the bubble air-protein interface along this growing process were followed.