Observation of the microstructure of a bi-extended hydrated dough and hydrated gluten under large strain and extremely low strain-rates: Results of an initial study

A small bubble-inflation device was developed for use in conjunction with a Low-to-Mid Range Magnification Digital Microscope. This device made it possible to observe the bi-extension of dough and gluten films at the top of a bubble under conditions that mimicked as closely as possible the typical GCW thicknesses, strains, strain rates and gaseous ambience found in dough during everyday proving or baking. For this stage, experiments were carried out at 20 °C. Stress-strain relationships were measured at strain rates ranging from 0.0006 to 0.09 s−1. The reduction in size yielded higher stress measurements compared to the results obtained from usual inflation devices (Alveograph®). Strain hardening in dough and hydrated gluten was observed regardless of the strain rate applied. A first trial using image analysis of the top of the bubble during deformation revealed useful information on the locations of the dough constituents and made it possible to reevaluate strain and strain-rate. The Hencky strain and stress at rupture were found to be of the order of 1.23 and 50–100 kPa respectively. This work illustrates the potential benefits of linking image analysis to a bubble-inflation device for the analysis of the mechanisms involved in the mechanical rupture of dough films.