Study of the pseudo-equilibrium during osmotic dehydration of apples and its effect on the estimation of water and sucrose effective diffusivity coefficients. http://dx.doi.org/10.1007/s11947-011-0621-8

Abstract

The study of the equilibrium is needed not only for modeling of the osmotic process as a unit operation but also for a better understanding of the mass transfer mechanisms involved in this kind of systems. A true equilibrium state usually takes very long time to achieve; therefore, a pseudo-equilibrium state is often employed.
Experimental pseudo-equilibrium states for water loss and solid gain during the osmotic dehydration of apple slices (5×50×50 mm3) at different osmotic syrup concentrations
(30%, 40%, 50%, and 60% (w/w) of sucrose) were evaluated. Four empirical mathematical methods (Slopes, Azuara, Zugarramurdi and Lupín, and Equal concentration) were used in order to calculate the pseudo-equilibrium values obtained and then to compare them against to the experimental ones. Additionally, the effective diffusion coefficients for water and sucrose were calculated by using those pseudo-equilibrium values. Experimental pseudoequilibrium values increased with concentration of the osmotic syrup, ranged between 24% and 56% for water loss and 11% and 28% for solid gain; the predicted seudoequilibrium values followed the same trend. The decreasing order of accuracy for pseudo-equilibrium values and effective diffusion coefficients, among the methodologies evaluated, was Equal concentration method > Azuara method > Slopes method > Zugarramurdi and Lupín
method. Although the Equal concentration method has no theoretical accuracy, it is independent of the kinetic data presenting a higher advantage over the other three
mathematical methods evaluated.