Ultrasound Effects on the Mass Transfer Processes during Drying Kinetic of Olive Leaves (<i>Olea Europea</i>, var. Serrana)

Abstract

The large amount of materials derived from olive trees pruning may constitute a source of compounds with antioxidant activity. The air drying of raw matter is a previous stage before extraction preserving the raw matter and avoiding the interference of water on the process but it constitutes a slow and high energy demanding process. In this sense, the application of high intensity ultrasound could affect the mass transfer rate. In order to address the influence of ultrasound on the drying process of olive leaves, air drying experiments were carried out (40°C and1 m/s) without (0 W) and with ultrasound application (8, 16, 25 and 33 kW/m3). The different drying conditions were tested by triplicate. To model the experimental data, diffusional models considering or not the external resistance to mass transfer were used. The model without considering external resistance did not fit well to the experimental data. However, the model including external resistance achieved percentages of explained variance above 99.7%. The influence of ultrasound on diffusivity was not significant but a significant dependence was found for the mass transfer coefficient, proportional to the power density applied.