Ultrasonic investigation of the effects of composition on the volume fraction of bubbles and changes in their relative sizes in non-yeasted gluten-starch blend doughs

Interactions between water, gluten and starch during dough mixing alter the aeration properties of dough. Effects of composition on dough gas volume fraction and relative changes in bubble sizes of non-yeasted gluten-starch (G-S) blend doughs were investigated using density measurements and an ultrasonic transmission technique, respectively. At fixed water content, greater gluten content increased the air volume fraction, while frequency-dependent ultrasonic attenuation coefficient and phase velocity measurements indicated that the bubble sizes in the G-S doughs were larger. The latter outcome may be due to mixing to optimal conditions such that shorter mixing times for doughs of high gluten content lessened the number of bubble subdivision events during mixing. The effect of increased water content on the attenuation coefficient implied a decrease in mean bubble radius as elucidated using an ultrasonic model. Time evolutions of attenuation coefficient and phase velocity for G-S blend doughs had a similar trend to those of non-yeasted wheat flour doughs. However, the shifts in the frequency of the peaks observed in the ultrasonic parameters were noticeably slower for G-S blend doughs, implying that G-S blend doughs were more stable against disproportionation.