Ultrasonic Investigation of the Effect of Mixing Under Reduced Pressure on the Mechanical Properties of Bread Dough

Abstract

Mixing is critical to attainment of a desirable gas cell distribution in dough. By varying mixer headspace pressure, changes in the mechanical properties of dough were investigated as a function of the dough's void concentration using low frequency (50 kHz) ultrasonic techniques. For the mixer used, this allowed the volume fraction of voids (Φ) to be varied from ≈0.01 to 0.08. The ultrasonic attenuation of longitudinal waves increased linearly with increases in Φ. If, as reported, pressure reductions during mixing decrease the number density of the voids but do not affect void size, the change in attenuation is proportional to the number of voids. By contrast, the velocity of longitudinal ultrasonic waves decreased dramatically with increasing Φ in the range 0.012 < Φ < 0.03, dropping from a value near that of water to values well below the velocity of sound in air. At higher Φ, the velocity decrease was less rapid. The longitudinal elastic modulus determined from these ultrasonic results shows that the mechanical properties of the dough are sensitive to the presence of gas bubbles. At low void fractions, the elastic behavior of dough is also influenced by changes in dough matrix properties.

Identification of Baking Expansion Phases of Leavened Dough Using an Experimental Approach

“…The calculated values of the density ρ for the experimental combinations ranged from 1.217 g cm −3 , for cultivar Bombona, to 1.229 g cm − 3 , for cultivar Finezja. They corresponded well with those ones measured experimentally by Chin and Campbell (2005) and Elmehdi et al (2004).…”

The bubble size distribution in wheat flour dough

“…A further reason for studying bubbles in dough is that dough exhibits extremely complex rheological properties (Bagley, Dintzis, & Chakrabarti, 1998), and bubble numbers and sizes will affect dough rheology (Bloksma, 1981(Bloksma, , 1990Carlson & Bohlin, 1978). For example, the rate of disproportionation of air bubbles in the dough is influenced by bubble sizes and by the separation between them (van Vliet, 1999), while the number density of bubbles has a remarkable effect on the rheological properties of the dough (Chin, Martin, & Campbell, 2005;Elmehdi, Page, & Scanlon, 2004). Despite the technological and scientific importance of acquiring quantitative data on the bubble size distribution in dough, dough's opacity and fragility have contributed to difficulty in acquiring these data.…”

“…Despite the usefulness of these studies for examining how mixing conditions potentially affect crumb cell structure (Campbell, 1991;Carlson & Bohlin, 1978), and for modelling the rheological behaviour of dough (Elmehdi et al, 2004), the validity of these bubble data is questionable since freezing and serial sectioning, or squashing of the dough, invariably affect the integrity of the sample. In addition, reconstruction of bubble size distributions from two-dimensional sections is methodologically difficult (Campbell, Rielly, Fryer, & Sadd, 1999;Martin et al, 2004;Underwood, 1970).…”

Probing thermal transitions and structural properties of gluten proteins using ultrasound

“…The full picture is very complex but the corollary is that the ultrasonic response is sensitive to many of the key structural and mechanical properties. Therefore, there is considerable interest in using ultrasound in the food industry to monitor food properties, provided that the samples are otherwise well characterized [11][12][13][17][18][19]. A longitudinal ultrasonic pressure wave, propagating through a fluid medium in the x-direction with a pressure field, w, is described by [20,21],…”

“…One ''new'' technique that has been developed and has shown great potential for evaluating the structural properties of viscoelastic materials is low-intensity ultrasound [11][12][13]. By subjecting the sample to low-intensity longitudinal ultrasonic waves, information about the mechanical and structural properties of the sample may be readily extracted.…”