Seyed Hadi Peighambardoust: Development of dough under shear flow

Dough mixing involves a combination of different deformation flows, e.g. shear and elongation. The complicated nature of the mixing makes it difficult to understand dough processing on a mechanistic level. Apart from that, a quantitative relation between the type of deformation in the mixing and resulting dough properties is still lacking. This indicates the importance of unraveling the complex process into most relevant deformation patterns such as simple shear and extensional flow in dough mixing. Literature studies mostly focus on well-known parameters such as process time, temperature, energy (time, rotational speed), etc. in dough processing. The question is not fully answered is that how kneading (shear versus extensional deformation) affects structure formation (gluten development) in the dough.

The overall objective of this thesis is to generate understanding of the relation between relevant process parameters in dough mixing and changes in product properties. This thesis focuses on the effect of well-defined deformation on the structure formation and properties of dough on various levels of detail. To reach this aim, a zero developed (ZD) dough was used as starting material. The ZD dough was compared with a flour–water mixture as starting material in z-blade mixing trials. The ZD dough constituted a good model for dough mixing studies to help study the different aspects of mixing. The physical properties of glutenin macro polymer (GMP), as the most relevant quality criterion for end-use quality of wheat at, was used to detect changes in the properties of the dough. This analysis provided the characterisation of the dough at the length scale of glutenin particles (micro-scale). In line with this analysis, changes in microstructure of the dough (meso-scale) and large-scale deformation rheological characteristics of the dough (macro-scale) were elucidated under a well-defined simple shear flow. Finally, an attempt was made to compare above-mentioned characterisation of the dough at two different process conditions. In this respect, a Couette-type device was introduced to study dough properties upon changing the flow profile from steady into transient shear flow in the device. The benefits of using this methodology in understanding the conventional dough mixing on a mechanistic level have been discussed. Last but not the least, the implications of the findings for bakery industry, the overall conclusions and recommendations for future studies in this regard, are discussed.