Diffusion mechanisms during the osmotic dehydration of Granny Smith apples subjected to a moderate electric field

Abstract

Osmotic dehydration is a process wherein foods are partially dehydrated by immersion in an aqueous hypertonic solution. Osmotic dehydration reduces the water activity of the food, thereby minimizing the potential growth of microorganisms and extending the shelf life of food products. A major disadvantage of the osmotic dehydration process is the long time required to reduce the water activity, which makes its industrial implementation impractical.The aim of this research is to determine the diffusion mechanisms in Granny Smith apples exposed to different electric fields varying from 0 to 17V/cm.Osmotic dehydration was performed at 40°C for both the conventional treatment and for the MEF treatment. The fruit/solution ratio used was 1:11 w/w to prevent and minimize the change in concentration of the solution during the experiment. The osmotic solution was exposed to electric fields of 0, 9, 13 or 17V/cm, respectively. To determine the diffusion mechanisms two phenomenological models were tested: Fick’s second law and Anomalous diffusion model.Sucrose diffusion in Granny Smith apples is highly influenced by the application of a MEF, meaning that as the application of the electric field increases, the higher the effective diffusion coefficient (Deff) becomes. The exponential decay from the Fick law, in the tail of the diffusion profile, does not represent the shape of the data. However, as the application of the electric field increases the fit of Fick’s model improves, and specifically for an electric field of 17V/cm it is observed that the behavior of the experimental data resembles the behavior predicted by Fick’s second law. The empirical parameter α for the anomalous diffusion model was always greater than one, but as the MEF increased, α was monotonically tending to one.