36D-2

            Mixing is a critical stage in breadmaking since it controls gluten development and gas cell nucleation in dough. Gas cells are important since they affect both the rheology of the dough and the quality of the final product. One tool capable of probing the effect of mixing on dough properties in a non-destructive manner is low-intensity ultrasound.

            The objective of this study was to use ultrasound to examine gas cell entrainment as a function of mixing time in doughs prepared with different levels of shortening.

            Doughs were made from red spring wheat flour with various amounts of shortening (0, 2, 4, 8 % w/w).  The doughs were mixed at atmospheric pressure or under vacuum (0.04 atm) for various times.  Ultrasonic velocity and attenuation (at 50 kHz) were measured in the doughs, as was dough density (from specific gravity measurements).

            As mixing time increased at atmospheric pressure, velocity and density decreased while attenuation increased.  For example, in control doughs, velocity decreased from 165 to 105 m.s^-1 and density from 1200 to 1050 kg.m^-3, while attenuation increased from 1800 to 2700 m^-1.  Superimposed on the overall decrease in velocity was a discernible peak in velocity at optimum mixing time.  Similar trends were observed for doughs prepared with shortening, but velocities and densities at a given mixing time were progressively lower as shortening levels increased. In doughs mixed under vacuum, little variation in velocity and density was observed with mixing time. However, changes in attenuation coefficient (from 600 to 1540 m^-1) suggested that ultrasound was sensitive to the changes in the properties of the dough matrix during dough development.

            This study showed the potential of ultrasound for probing the effect of mixing times and ingredients on dough properties, and thus the possibility of on-line ultrasonic quality control in the baking industry.