Osmotic dehydration of apples —effects of agitation and raw material characteristics

Abstract

The effects of agitation and structural differences on osmotic dehydration were investigated. Osmotic dehydration was performed in an agitated vessel at 20 °C using a 50% sucrose solution as the osmotic medium. The impeller's Reynolds number was used for agitation quantification. Samples were separated into inner and outer apple parenchymatic tissue, the intercellular space interconnectivity and aspect ratio (length to width ratio) being higher in inner than outer tissue. Structural differentiation revealed a strong effect on process responses. Solid gain (kg/kg i.m.) was higher in inner than in outer apple parenchymatic tissue independently of agitation level. Water loss (kg/kg i.m.) was lower in inner than outer apple parenchyma at the same Reynolds number. Water loss was higher in the turbulent flow region than in the laminar flow region. Thereby, external mass transfer limitations were verified for our experimental conditions. Solid gain did not show significant differences between laminar and turbulent flow regions. The data indicate that free convection is the mechanism used by the solution in pore penetration, although lack of understanding of this phenomenon at the cell level prevented conclusions from being drawn. Attempts to explain experimental variations revealed indications suggesting the influence of initial bulk density and initial water content on water loss and solid gain.