Stress Concentration Analysis in A Heterogeneous Dough Gas Cell Wall at The Microscale: Effect of Gluten/Starch Interaction and Rheological Moduli Ratio
Bread dough is often described as a dispersion of gas cells in a continuous gluten/starch matrix . The final bread crumb structure is strongly related to gas cell walls (GCWs) rupture during baking. At the end of the proofing and during baking, part of the thinnest GCWs between expanding gas cells is reduced to a gluten film of about the size of a starch granule [2-4]. When such size is reached gluten and starch granules must be considered as interacting phases in order to account for heterogeneities and appropriately describe GCW rupture. The strain and strain rate involved during baking are of the order of 0.3-2.5 and 0.003 s-1.
Attempts to numerically understand GCW rupture are usually not performed at the GCW scale and often considered GCWs as continuous [5-8]. To our best knowledge, the most relevant papers that accounted for heterogeneities only dealt with the gluten/starch interactions and their impact on the mechanical behavior of dough film [2,6,9].
The impact of gluten/starch interactions (cohesion or non-cohesion) and rheological moduli ratio on the mechanical behavior of GCW under unidirectional extension was numerically assessed in 2D/3D using the linear and nonlinear Structural Materials Modules available in COMSOL Multiphysics® software. A first linear viscoelastic 1-element generalized Maxwell (1-EGM) model which is theoretically adapted for infinitesimal strains (<0.1) and small strain rates was performed. A second 1-EGM hyperelastic approach was performed to account for a finite strain (large strain>1). The Gluten/starch interactions were modeled using the pair “Thin Elastic layer” boundary condition to account for the gluten/starch interface without modeling a dedicated domain.
Advantages and disadvantages of both the linear and non-linear approaches of viscoelasticity were discussed. Locations of maximal stresses where the GCW was most likely to rupture were identified. The gluten/starch granule rheological moduli ratio were found to have a great effect on the amount of Von Mises stress reached in the GCW. Experimental investigations are needed in order to identify where the rupture is really initiated and bring light to the numerical results.
 Gan, Z., et al., The microstructure and gas retention of bread dough. Journal of Cereal Science, 1990. 12(1): p.15-24.
 Sandstedt, R., The microscopic structure of bread and dough. Cereal Chem., 1954. 31: p.43-49.
 Bloksma, A.H., Rheology of wheat flour doughs. Journal of Texture Studies, 1972. 3(1): p 3-17.
 Dobraszczyk, B.J., The rheological basis of dough stickiness. Journal of Texture Studies, 1997. 28(2): p.139-162.
 Mohammed, M.A.P., Mechanical characterization and micromechanical modeling of bread dough. Journal of Rheology, 2013. 57(1): p.249-272.
 Hayman, D.A., Factors controlling gas cell failure in bread dough. Cereal Chemistry, 1998. 75(5): p. 585-589.
 Singh, A.P. and M. Bhattacharya, Development of dynamic modulus and cell opening of dough during baking. Journal of Texture Studies, 2005. 36(1): p.44-67.
 Dunnewind, B., The kieffer dough and gluten extensibility rig ‐ an experimental evaluation. Journal of Texture Studies, 2003. 34(5‐6): p.537-560.
9. Baker, J.C., M.D. Mize, Effect of temperature on dough properties - II. Cereal Chemistry, 1939. 16: p. 682-695.