DETERMINATION OF ULTRASONIC‐BASED RHEOLOGICAL PROPERTIES OF DOUGH DURING FERMENTATION1

Abstract

ABSTRACT An ultrasonic technique was used to study the changes of the rheological properties of dough during fermentation at 37C and compared with the extensional properties of fermented dough obtained from tensile tests carried out in a Universal Testing Maching. The velocity and attenuation of a longitudinal wave (P‐wave) propagated through the dough samples were measured and analyzed to obtain the viscoelastic moduli of the dough; the storage modulus M' and the loss modulus M''. These moduli include both the bulk and the shear moduli. A wavelet analysis also was used to determine the effect of frequency on the ultrasonic‐based viscoelastic moduli and the effect of the fermentation process on the ultrasonic velocity dispersion. A decrease in ultrasonic velocity was observed with increasing fermentation times. Ultrasonic waves were strongly attenuated in the dough subjected to long fermentation times and fermentation had a large influence on the viscoelastic moduli of the dough. The ultrasonic velocity increased with increasing frequency, clearly showing the viscoelastic nature of the fermented dough. The analysis also showed significant ultrasonic velocity dispersion upon fermentation. Ultrasonic measurements yielded results that agreed with those obtained from conventional rheology commonly used to characterize the extensional properties of dough. Both tests clearly showed the loss of elasticity by the dough samples upon fermentation.