Mass transfer mechanisms occurring in osmotic dehydration of guava

Two osmotic dehydration modes were applied to guava segments immersed in a 65 °Brix sucrose solution at 30, 40 and 50 °C: under constant atmospheric pressure and using a pulsed vacuum (5 min under vacuum, then at atmospheric pressure). The effective diffusivity in the liquid phase, De and the kinetic constants of net mass transfer, K and K0, were determined by fitting the experimental data to mathematical models. The highest effective diffusivities were obtained with pulsed vacuum at 40 and 50 °C on account of the hydrodynamic mechanism, with solids diffusion overcoming dehydration at the beginning of the process, at 30 and 40 °C. The effect of temperature on mass transfer kinetics, predictable by the Arrhenius equation, is more relevant at atmospheric pressure, where the pseudo-diffusion mechanism exerts the controlling role.