A recently developed technique, based on ultrasonic wave propagation, was applied to study the effect of storage time on the retrogradation process of wheat starch extrudates during storage at room temperature. A specifically designed experimental setup enabled to propagate in situ ultrasonic waves continuously for several days at constant water content and storage temperature (similar to 34% water and 25 degrees C). The velocity and the attenuation of the ultrasonic waves changed as a result of the recrystallisation process of amylopectin molecules of wheat starch samples during storage. The propagation of ultrasonic waves, acting as a dynamic mechanical deformation at high frequency (10 MHz), gave access to the complex longitudinal modulus that, compared to the Complex Young modulus obtained from low frequency DMA, enabled a better insight of the changes in viscoelastic behaviour of starch extrudates during retrogradation. The results of the ultrasonic monitoring of starch retrogradation were correlated with those obtained from X-ray diffraction and differential scanning calorimetry. The present study demonstrated the potential of the ultrasonic technique in detecting the changes in physical properties of concentrated starch systems. (c) 2005 Elsevier Ltd. All rights reserved.