Drying of ultrasound pretreated apple and its selected physical properties

The aim of this work was to investigate the utilization of ultrasound as a mass transfer enhancing method prior to drying of apples tissue. Ultrasound power was provided at a frequency of 35 kHz for 10, 20 and 30 min in the ultrasound bath. Apple cubes were dried using convection method in 70 degrees C and at air velocity of 1.5 m/s. The effects of ultrasound pre-treatment upon drying were investigated. The ultrasound treatment caused reduction of the drying time by 31% in comparison to untreated tissue. The ultrasound treated apples exhibited between 9% and 11% higher shrinkage, 6-20% lower density, and porosity of 9-14% higher than untreated samples. Considerable differences in the density and porosity of the dried apple with and without ultrasonic application were confirmed by scanning electron microscopy image analysis of the investigated tissue. Moreover, ultrasound application caused alteration of rehydration properties in comparison to untreated sample. (C) 2012 Elsevier Ltd. All rights reserved.