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Dynamic and Elongation Rheology of Yeasted Bread Doughs

¹New Zealand Institute for Crop & Food Research Limited, Private Bag 4704, Christchurch, New Zealand. ²Corresponding author. E-mail: newberrym@ crop.cri.nz. Phone: 64.3.325.6400. Fax: 64.3.325.2074. ³Institute for High Performance Computing, National University of Singapore, Singapore 118261. ⁴School of Aeronautical, Mechanical and Mechatronic Engineering, The University of Sydney, NSW 2006, Australia. ⁵CSIRO Plant Industry, GPO Box 1600, Canberra, ACT 2601, Australia. ⁶Quality Wheat Cooperative Research Centre Limited, Locked Bag 1345, North Ryde, NSW 1670, Australia.

The rheology of yeasted bread doughs is a little-studied field despite yeast's importance in developing bread structure. A method of thermally inactivating the yeast within mixed bread doughs was developed to overcome the difficulty of yeast fermenting during rheological measurements. Sample stabilization by preshearing of dough samples at a stress amplitude of 1 Pa at 1 Hz for 10 sec improved the reliability of small amplitude oscillatory shear measurements, and resting 20 min within the rheometer was sufficient to produce reliable and consistent observations. Small amplitude oscillatory shear measurements were unable to detect any differences between yeasted and nonyeasted doughs nor any changes in linear viscoelastic properties due to fermentation. However, large strain uniaxial elongation measurements of yeasted doughs revealed a significant progressive decrease in elongational viscosities with fermentation. Size-exclusion HPLC analysis of yeasted doughs showed an increase in unextractable polymeric dough proteins, which were interpreted as evidence of cross-linking and therefore a potential improvement in dough properties. The apparent contradictions between uniaxial elongation and SE-HPLC studies of fermenting yeasted doughs can be attributed to gas bubbles within the dough interrupting the increasingly cross-linked protein network, resulting in the rheological weakness observed for fermenting yeasted doughs.