Use of ultrasound to increase mass transport rates during osmotic dehydration

Experiments on osmotic dehydration of 1 cm apple cubes in 70 degrees Brix sucrose solution using ultrasound treatment were carried out at 40, 50, 60 and 70 degrees C. Acoustic pressure and frequency was measured to characterize the ultrasonic bath. Mass transfer was described by Fick's unsteady state diffusion equation. Art important influence of the solution temperature on water transport was obtained. Measured wafer diffusivity coefficients (D-W) ranged from 2.6 x 10(-10) m(2) s(-1) at 40 degrees C to 6.8 x 10(-10) m(2) s(-1) at 70 degrees C. Similar sucrose gain was measured at different temperatures, with an average effective sucrose diffusivity coefficient (D-S) (7.9 +/- 0.2) x 10(-11) m(2) s(-1). Similar experiments were performed under dynamic agitation conditions. A significant decrease in water and solute transport rates was detected when agitation was applied instead of sonication. (C) 1998 Elsevier Science Limited. All rights reserved.