0960–3085/03/$23.50+0.00 # Institution of Chemical Engineers www.ingentaselect.com =titles =09603085.htm Trans IChemE, Vol 81, Part C, September 2003 MONITORING DOUGH FERMENTATION USING ACOUSTIC WAVES H. M. ELMEHDI 1,2, * , J. H. PAGE 1 and M. G. SCANLON 2 1 Department of Physics and Astronomy, University of Manitoba, Winnipeg, Canada 2 Department of Food Science, University of Manitoba, Winnipeg, Canada F ermentation of the sugars in bread dough produces carbon dioxide which diffuses through the dough matrix into the gas cell nuclei formed during dough mixing. As a result, the void fraction of the dough increases and dough density decreases. It is shown in this paper that low intensity ultrasound can be used to monitor changes in the void fraction of this opaque material, thus providing real-time information on changes in the structure of the dough during fermentation. Doughs were mixed under two different mixer headspace conditions, and the ultrasonic velocity and attenuation measured as a function of fermentation time. The results of the ultrasonic experiments were compared with changes in dough density (measured independently but under the same experimental conditions). As fermentation time increased (and gas cells expanded), the ultrasonic velocity decreased and the attenuation increased. At early fermentation times, a substantial drop in velocity was observed before the density changed appreciably, indicating that yeast activity has two independent effects on dough properties: modifying the elasticity of the dough matrix and expanding the gas cells. Ultrasound therefore has the potential to provide novel information on technological issues of critical importance to the cereals’ processing industry. Keywords: ultrasound; bread dough; fermentation; density; structure. INTRODUCTION Measurements of ultrasonic velocity and attenuation have been used to characterize the physical properties of many food systems (Ghaedian et al. , 1998; Gunasekaran and Ay, 1996; McClements et al., 1993; Mizrach et al. , 1989). Because ultrasonic techniques have the advantage of acquir- ing measurements rapidly, the measurement of ultrasonic properties can in some cases be performed on-line (Forrest, 1996; Saggin and Coupland, 2001). The ultrasonic velocity and attenuation coefcient can then be related to various physical properties of the foods being tested, or they can be used to control the process conditions of a particular unit operation. Ultrasonic evaluations of the properties of dough-based products are not as widespread as they are in other sectors of the food and chemical processing industries. Part of the reason appears to be the strong attenuation of ultrasound in dough (Le ´tang et al., 2001; Moorjani, 1984). Therefore, much use is made in breadmaking processes of empirical measurements of the mechanical properties of dough using instruments such as the farinograph, the alveograph and the mixograph (Bloksma and Bushuk, 1988) although large strain (Charalambides et al., 2002; Safari-Ardi and Phan- Thien, 1998) and small strain (Edwards et al., 2002; Safari- Ardi and Phan-Thien, 1998) measurements of fundamental mechanical properties of dough and dough-based products are receiving greater emphasis. One ingredient that affects the mechanical properties of dough is its gas content (Charalambides et al. , 2002). Indeed, it has been stated that the various operations of breadmaking ‘may be viewed as a series of aeration stages’ (Campbell et al., 1998). Therefore, a technique such as ultrasound, which is very sensitive to the numbers and sizes of gas inclusions within a solid or liquid matrix (Leighton, 1997), appears to have great potential for process monitor- ing of dough properties, either at-line or on-line. The objective of this paper is to show how low-frequency ultrasound (50 kHz) can be used to study the dynamics of dough fermentation. By monitoring the changes in ultra- sonic velocity and attenuation that occur during fermenta- tion, information on the effect of fermentation on both dough matrix properties and the expansion of the gas cells within the dough matrix is obtained. METHODS AND MATERIALS Dough samples were prepared from our milled from Canadian Western Red Spring wheat (CWRS, grade no. 1), with a our protein content of 12.4%. All wheat was milled in the Canadian International Grains Institute (CIGI) pilot mill (Winnipeg, Manitoba, Canada). Dough was prepared 217 *Present address: Agriculture and Agri-Food Canada, Cereal Research Centre, 195 Dafoe Road, Winnipeg, Manitoba, Canada R3T 2M9.