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Ultrasonic investigation of dough mixing and proofing. H. M. ELMEHDI (1), J. H. Page (1), M. G.
Scanlon (2), and M. J. W. Povey (3). (1) Dept. of Physics and Astronomy, University of Manitoba,
Winnipeg, MB, Canada R3T 2N2; (2) Dept. of Food Science, University of Manitoba, Winnipeg, MB,
Canada R3T 2N2; (3) Procter Dept. of Food Science, University of Leeds, Leeds, LS2 9TJ, UK.
In this presentation we show how ultrasonic techniques can be used in
the non-destructive evaluation of the mechanical properties of dough. This approach is based on measuring
the velocity and attenuation of longitudinal ultrasonic waves as they propagate through the dough, giving
information on both viscoelastic and structural properties of the dough. The most striking behaviour is the
strong influence of the gas cells or voids on both the ultrasonic velocity and attenuation. We investigate this
effect quantitatively in two sets of well-controlled experiments performed at an ultrasonic frequency of 45
kHz. In the first set of experiments, we vary the concentration of the gas cells in unyeasted dough by
changing the mixing pressure, allowing the volume fraction of voids, phi, to be varied from about
0.01 to 0.08. As phi is increased, there is a large decrease in the velocity and a substantially linear
increase in the attenuation, allowing the gas cell concentration to be directly measured. In the second set of
experiments, we extended our measurements to investigate yeast activity in the dough, so that we can use
our ultrasonic experiments to monitor the increase in the gas cell size due to CO(2) production and retention
during fermentation. We find a large decrease in the velocity and an increase in the attenuation as the gas
cells grow in size. These results demonstrate the potential for using ultrasound as a non-destructive, cheap
and accurate tool for determining the volume fraction of gas cells in dough.
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