Ultrasonic Investigation of the Effect of Vegetable Shortening and Mixing Time on the Mechanical Properties of Bread Dough

Abstract

Mixing is a critical stage in breadmaking since it controls gluten development and nucleation of gas bubbles in the dough. Bubbles affect the rheology of the dough and largely govern the quality of the final product. This study used ultrasound (at a frequency where it is sensitive to the presence of bubbles) to nondestructively examine dough properties as a function of mixing time in doughs prepared from strong red spring wheat flour with various amounts of shortening (0%, 2%, 4%, 8% flour weight basis). The doughs were mixed for various times at atmospheric pressure or under vacuum (to minimize bubble nucleation). Ultrasonic velocity and attenuation (nominally at 50 kHz) were measured in the dough, and dough density was measured independently from specific gravity determinations. Ultrasonic velocity decreased substantially as mixing time increased (and more bubbles were entrained) for all doughs mixed in air; for example, in doughs made without shortening, velocity decreased from 165 to 105 ms(-1), although superimposed on this overall decrease was a peak in velocity at optimum mixing time. Changes in attenuation coefficient due to the addition of shortening were evident in both air-mixed and vacuum-mixed doughs, suggesting that ultrasound was sensitive to changes in the properties of the dough matrix during dough development and to plasticization of the gluten polymers by the shortening. Due to its ability to probe the effect of mixing times and ingredients on dough properties, ultrasound has the potential to be deployed as an online quality control tool in the baking industry.

Effects of composition on dough development and air entrainment in doughs made from gluten-starch blends

“…The sub-sample was placed in a 25 ml specific gravity bottle (Kimble Glass Inc., Vineland, NJ, USA) previously filled with distilled water. The density of the dough sub-sample was calculated from the weight of water displaced (Mehta et al, 2009). Five subsamples were used for density determination of each dough sample.…”

“…If differences in composition alter the extent of binding between starch and gluten, then one may also expect that the development of a good gas-holding film will be affected so that the volume fraction of air entrained into the dough will be altered. One way to determine the amount of air occluded during mixing is to measure dough density (Campbell et al, 1993;Elmehdi et al, 2004;Mehta et al, 2009). However, in wheat flour doughs, density not only varies with dough consistency (Peighambardoust et al, 2010), but is strongly dependent on time of mixing (Baker and Mize, 1937;Hoseney, 1985;Mehta et al, 2009).…”

“…In the breadmaking process three important tasks are performed during dough mixing: (1) blending and hydrating ingredients (absorption of water by various flour components), (2) developing the gluten polymers in the dough to create a good gas retaining film structure, and (3) occluding gas bubbles into the dough and subdividing them (Baker and Mize, 1941;Campbell et al, 1998;Mehta et al, 2009). It is thought that these tasks interact during the mixing process (Hoseney, 1985;Chin and Campbell, 2005a) and the extent to which interactions do occur is likely to alter the properties of the mixed dough.…”

“…Although torque recording mixers will provide good information on ingredient hydration and gluten film development, the nature of air occlusion during mixing has to be characterized by measuring the air volume fraction and the bubble size distribution in the dough after mixing (Campbell et al, 1998). The amount of air entrained and its subdivision into a particular bubble size distribution depends on mixer type (Whitworth and Alava, 1999;Peighambardoust et al, 2010), headspace pressure in the mixer (Elmehdi et al, 2004;Chin and Campbell, 2005a), moisture content (Chin et al, 2005;Peighambardoust et al, 2010), mixing time (Campbell et al, 1998;Mehta et al, 2009) and ingredients (Chin et al, 2005;Mehta et al, 2009). Unravelling the various mechanisms operating during mixing, in order to understand how ingredients and mixing process parameters affect the resulting dough properties, is not a trivial task.…”

Effects of fat replacement on properties of whole wheat bread

“…While lipids lubricate (Ghotra, Dyal, Narine, 2002) and plasticize the dough, in particular the gluten polymers (Mehta et al, 2009), fat should be restricted or reduced in the diet because it is the most important obesity factor (Valenzuela, Sanhueza, 2008) and non-communicable chronic disease factor (Brasil, 2005a).…”