Modeling of kinetics, equilibrium and distribution data of osmotically dehydrated carambola (Averrhoa carambola L.) in sugar solutions

Osmotic dehydration (OD) of carambola slices in sucrose, fructose and glucose solutions has been carried out to evaluate water and solute diffusivities, as well as the final impregnation–dehydration levels of the fruit. OD kinetics was performed in sugar solutions (50 g/100 g) at 45, 60 and 75 °C during 10 h using a syrup-to-fruit mass ratio of 15:1. An analytical solution for unsteady-state mass transfer based on Fick’s second law of diffusion was used for the mathematical description of water loss and solute gain kinetics. By following a central composite design, additional OD tests were conducted to evaluate the effect of solute concentration (35.9–64.1 g solute/100 g solution) and process temperature (38.8–81.2 °C) on the equilibrium and distribution data for both solutes and water. Under the described experimental conditions, effective water diffusivity was in the range of 1.00–3.74 × 10−9 m2/s, whereas values for sucrose, fructose and glucose diffusivities were between 0.58–1.79 × 10−9, 0.56–1.34 × 10−9 and 0.56–1.88 × 10−9 m2/s, respectively. Results demonstrated that sucrose can be considered a better osmotic agent than fructose and glucose for OD of carambola, favoring greater water loss-to-solute gain ratios at comparable mass transfer rates.