Anisotropic diffusion during osmotic dehydration of celery stalks in salt solution

• Experimental investigation of anisotropic mass transfer during osmotic dehydration of celery.
• Mathematical modeling of the process, considering two geometries: cubic and cylindrical.
• Estimation of equilibrium moisture loss and solid gain using a two parameter method.
• Estimation of moisture and salt effective diffusivities in x, y, z and r directions in the celery.
• Developing correlations for equilibrium moisture loss and solid gain and effective moisture and salt effective diffusivities in celery.

In this study, mass transfer during osmotic dehydration of bulk of celery stalks in NaCl salt solution was investigated. Experiments were carried out in the three initial solution concentrations of 10%, 18% and 25% (w/w) and at the three temperatures of 35 °C, 45 °C and 55 °C. The fruit to solution volume ratios were considered 1:3. Due to the asymmetric structure of the celery stalks, two different geometries of cylindrical and cubical were considered for mathematical modeling of the dehydration process. A two-parameter model was used to evaluate the equilibrium values of moisture loss and solute gain by the samples. Water and salt effective diffusivities were obtained using the first six terms of the series solution of analytical solution of Fick's second law in the cubical and cylindrical geometries. Two different groups of celery stalks were used for estimation of moisture and salt effective diffusivities in different directions. Predictions of the mathematical model in both geometries were in agreement with the experimental data. The water and salt effective diffusivities in z direction (ranged from 0.972 × 10−9 to 3.663 × 10−9 (m2/s)), were always much higher than those in x, y and r directions (ranged from 1.031 × 10−10 to 6.919 × 10−10 (m2/s)). The values of water and salt effective diffusivities in z direction were close to each other in both geometries. The water and salt effective diffusivities were increased with increasing the initial solution concentrations and temperatures.