Extensional dough rheology – Impact of flour composition and extension speed

• Strain hardening indices from dough tensile measurement were not rate dependent.
• Protein composition affects strength and extensibility of gluten, not those of dough.
• Starch granules aligned within the gluten network are in the direction of extension.
• Both gluten network and starch granules contribute to dough extensional properties.

The rheological properties of dough have an essential role in processing handling and quality of baked products. Understanding how measurement parameters impact dough strain hardening behaviour and how dough microstructure changes during the extensional deformation measurements is important for the evaluation of dough rheological properties. Four wheat flour samples were used in this study. They had either a low (9%) or high (13%) protein content and a glutenin-to-gliadin ratio of 0.35:1 or 0.7:1. The uniaxial extensional measurements were performed at three different extension speeds of 60, 120 or 600 mm/min, respectively. A typical characteristic of viscoelastic materials was obtained, showing that the maximum extension (Emax) and maximum resistance (Rmax) were dependent on the measurement speed, whereas the strain hardening indices were found to be independent on the speed. The differences in glutenin-to-gliadin ratios did not show a significant influence on Emax and strain hardening behaviour of dough but they affected the strength and extensibility of rehydrated gluten. The confocal microscopic in situ tensile experiments show that starch granules became aligned within the gluten network in the direction of extensional force. This indicates that both the re-arrangement of gluten network and starch granules contribute to the extensional rheological properties of dough.