The Self-Enforcing Starch–Gluten System—Strain–Dependent Effects of Yeast Metabolites on the Polymeric Matrix

Abstract

The rheological behaviour of dough during the breadmaking process is strongly affected by the accumulation of yeast metabolites in the dough matrix. The impact of metabolites in yeasted dough-like concentrations on the rheology of dough has not been characterised yet for process-relevant deformation types and strain rates, nor has the effect of metabolites on strain hardening behaviour of dough been analysed. We used fundamental shear and elongational rheometry to study the impact of fermentation on the dough microstructure and functionality. Evaluating the influence of the main metabolites, the strongest impact was found for the presence of expanding gas cells due to the accumulation of the yeast metabolite CO2, which was shown to have a destabilising impact on the surrounding dough matrix. Throughout the fermentation process, the polymeric and entangled gluten microstructure was found to be degraded (−37.6% average vessel length, +37.5% end point rate). These microstructural changes were successfully linked to the changing rheological behaviour towards a highly mobile polymer system. An accelerated strain hardening behaviour (+32.5% SHI for yeasted dough) was promoted by the pre-extension of the gluten strands within the lamella around the gas cells. Further, a strain rate dependency was shown, as a lower strain hardening index was observed for slow extension processes. Fast extension seemed to influence the disruption of sterically interacting fragments, leading to entanglements and hindered extensibility.

Strain-dependent assessment of dough’s polymer structure and functionality during the baking process

“…The true compression speed was adjusted according to the final sample height of each sample and corrected to reach comparable strain-strain rate combinations. The resulting force-displacement-curves were used to calculate the biaxial strain ε b , the biaxial strain rate , and the apparent biaxial viscosity η b * according to [ 10 ]. Further, the strain hardening index was calculated by extracting the stress values for deformations of 0.3, 0.4, 0.5, 0.6, 0.7 0.8, 0.9 and 1.0 for each displacement speed and temperature.…”

“…So far, research has focused on the behavior of highly connected polymeric wheat dough systems under elongational deformation upon thermal treatment. Conversely, the integrity of the wheat dough network cannot be granted in practice, as yeast metabolites, generated during the fermentation process, affect the functionality of the gluten network along the bread making process [ 10 , 20 ]. The impact of the degradation of the well branched structure on wheat dough functionality has not been quantified yet and will be the focus of this work.…”

“…The dough systems used in this work are standard non-yeasted wheat dough and yeasted wheat dough. In comparison to the standard wheat dough system, the microstructure of yeasted dough has been shown to be less branched, as the microstructure of yeasted dough is markedly affected by the degrading effects of yeast fermentation [ 10 , 21 ]. Beside this, secondary yeast metabolites were not shown to affect the network structure or functionality significantly [ 10 ].…”

Micro-Scale Shear Kneading—Gluten Network Development under Multiple Stress–Relaxation Steps and Evaluation via Multiwave Rheology

“…This relaxation step is important for network formation, as it enables interconnection during recoil and gluten strand relaxation. With this relaxation, the material is able to reduce the inner shear-induced tension, and protein recoil takes place [ 37 ]. These kneading pauses, together with the gradually increasing deformation due to the asymmetric deflection of the rheometer geometry, enhance the interconnection and relaxation processes in the dough matrix and support crosslinking throughout the whole sample cross-section.…”

Monitoring the Effects of Hemicellulase on the Different Proofing Stages of Wheat Aleurone-Rich Bread Dough and Bread Quality

“…The proportion of β-sheet significantly enhanced at a dosage of 40 mg kg −1 of flour, and the growing rate of proportion of β-sheet gradually raised with proofing. It had been stated by Alpers et al [49] that an increase in the proportion of β-sheet indicate good gluten viscoelasticity and baking quality. Moreover, the addition of hemicellulase significantly reduced the α-helix/β-sheet ratio in each proofing stage (Figure S2).…”