Modification of cell structure and mass transfer in potato tissue by contact ultrasound

The application of contact ultrasound in food drying processes can increase drying rates of fruit and vegetable products. In order to get a deeper understanding of the mechanisms involved this study dealt with the analysis of changes in tissue structure and mass transfer in potato (cultivar Belana) during a contact ultrasound treatment. Individual potato cylinders were sonicated on a stainless steel screen that served as sample supporting and sound transmitting surface. Cell injury and water content were analyzed in different tissue layers in dependence of sonication time and intensity. Although ultrasound related cell disruption was limited to a thin tissue layer in direct vicinity to the sonicated surface, mass transfer was influenced throughout the complete sample cylinder with a height of 1 cm. The improved water removal from the product could thus be attributed to ultrasound effects affecting mass transfer at tissue level, e.g. microstirring, reduction of boundary layers, sponge effect, absorption heating and structural changes. Ultrasound effects observed at ambient conditions could be transferred to convective drying of potato cylinders at 70 °C.

► Mechanisms of action of contact ultrasound applied in food drying are analyzed. ► Potato cylinders are treated on a screen used as sample supporting and sound transmitting surface. ► Contact ultrasound effects on water content and cell injury are evaluated. ► Ultrasound related cell disruption is limited to a thin tissue layer at the sonicated surface. ► Results show that contact ultrasound affects mass transfer at tissue rather than cellular level.