Blanching of Strawberries by Ohmic Heating: Effects on the Kinetics of Mass Transfer during Osmotic Dehydration

The effect of blanching by ohmic heating (OH) on the kinetics of osmotic dehydration of strawberries was studied. Ohmic heating parameters obtained at two temperatures (65 and 85 °C). The osmotic dehydration (OD) parameters are the temperature (26 and 37 °C) and the sucrose in osmotic solution (30–70 °B). An approximate solution of Fick’s law for unsteady state mass transfer in spherical configuration has been used to calculate the effective diffusion coefficients of water and sucrose. Results show that ohmic heating increases drastically the mass transfer and the effective diffusion rates. After 4 h of OD (without OH) in a sucrose solution (at 37 °C and 70 °B), the dry matter of the untreated strawberry halves was 20.3%; while it reached 68% when OD was combined with blanching by OH at 85 °C for 3-min. Ohmic blanching permits the effective damage of cells by combination of electrical and thermal effects. That result has an important enhancement of water and sugar transfers during osmotic dehydration of strawberries.