Observation of wheat flour doughs under mechanical treatment using confocal microscopy and classification of their microstructures

• A novel approach for coupling properties and structure of food systems.
• Dynamic observation of wheat flour doughs under mechanical treatment.
• Gluten network evolution depending on deformation time and level.
• A qualitative and quantitative study based on image texture analysis.

RheOptiCAD® is a cell allowing observation of microstructures under thermo-mechanical treatments. Using the device fitted on a confocal microscope, wheat flour doughs containing 3 levels of water were studied. Dough were placed between 2 parallel plates and submitted to motion of the bottom one. Temperature was controlled and fixed at 20 °C. Methodology and experimental parameters, but also balance between optical and mechanical ones are described and justified to set a dynamic observation in real time. Rhodamine B labeled gluten network was observed under dynamic mechanical treatment, i.e. a 0.4 mm-0.3 Hz oscillation applied during 30 s. The evolution of the gluten network microstructure along time of deformation and depending on the recipe was studied. Image sequences are presented to visualize the qualitative differences in the network. Differences in microstructures were observed. A grey scale mathematical morphology is proposed to qualify and quantify these differences. Images can be separated according to the level of orientation of the network and to the local protein concentration in the gluten fibers.