Accelerated drying of button mushrooms, Brussels sprouts and cauliflower by applying power ultrasound and its rehydration properties

The aim of this work was to use ultrasound as a pre-treatment method prior drying of mushrooms, Brussels sprouts and cauliflower in order to achieve reduction in drying time and to understand the effect of the ultrasound in mass transfer process, where diffusivity is the limiting step in the process. Pre-treatment with 20 kHz probe and 40 kHz bath for 3 and 10 min have been compared with blanched (80 °C/3 min) and untreated samples. The procedures used were either freeze drying or conventional drying at a temperature of 60 °C and air velocity (v = 0.3 m/s) for sonicated, blanched and untreated samples. The effect of ultrasound and blanching pre-treatments on weight and moisture loss/gain, upon drying and rehydration were investigated. The drying time after ultrasound treatment was shortened for all samples, as compared to untreated. The rehydration properties (weight gain, %) were found to be the best for freeze-dried samples which showed weight gains for mushrooms (45.3%), Brussels sprouts (21.4%) and cauliflower (51%). The rehydration properties for ultrasound treated samples were higher than those for untreated samples.