High frequency ultrasonic techniques dedicated to food physical properties assessment

Usually, viscoleastic properties of materials (complex shear moduli and viscosity) are evaluated with rheometers which can give G', G'' for instance, on wide bandwidths thanks to the Time Temperature Superposition principle. It is clear that the knowledge of such properties is very interesting on a fundamental point of view because infonnation on material microstructure can be deduced from master curves. On a more practical point of view, it can be used to improve fabrication processes, to perform quality controls, especially in food industry and engineering. This powerful method can fail to give large bandwidth information in several cases: phase transition of the material with temperature, volume to be analyzed too small, bad morphology of the sample. In order to overcome such a difficulty, it is possible to use ultrasonic waves. This paper, dedicated to high frequency methods (from a few kHz to many MHz) presents a review of existing methods and improvements developed in our labs. Several applications in the domain of food engineering will be given in order to prove the huge interest of high frequency approaches which are sometimes neglected compared to classical low frequency rheology. (Résumé d'auteur