Shear viscosity investigation on mango juice with high frequency longitudinal ultrasonic waves and rotational viscosimetry

Ultrasonic velocity and attenuation measurements were performed on mango juices at 25 MHz in order to estimate longitudinal viscosity. Juices were extracted from fruits, removed periodically from fruit batches undergoing ripening for 3 weeks under controlled conditions. The correlation between longitudinal viscosity and apparent dynamic shear viscosity, obtained from flow tests, showed that up to 12-13 wt.% of Soluble Solids Content (SSC), the juices presented a Newtonian behavior. In this case the relation between longitudinal viscosity measured by ultrasound and shear viscosity measured by flow tests was very simple leading to the conclusion that ultrasound could replace rotating viscosimeters for specific applications. Over this limit, the results were also clearly correlated but the correlation depended on the shear rate because of the shear thinning behavior of the juices certainly due to soluble pectins. The use of longitudinal ultrasonic waves as a tool for viscosity determination on large batches of samples is discussed at the end of this communication. (Résumé d'auteur