OSMOTIC DEHYDRATION OF APPLES - EFFECTS OF AGITATION AND RAW-MATERIALCHARACTERISTICS

The effects of agitation and structural differences on osmotic dehydra tion were investigated. Osmotic dehydration was performed bt an agitat ed vessel at 20 degrees C using a 50% sucrose solution as the osmotic medium. The impeller's Reynolds number was used for agitation quantifi cation. Samples were separated into inner and outer apple parenchymati c tissue, the intercellular space interconnectivity and aspect ratio ( length to width ratio) being higher in inner than outer tissue. Struct ural differentiation revealed a strong effect on process responses. So lid gain (kg/kg i.m.) was higher in inner than in outer apple parenchy matic tissue independently of agitation level. Water loss (kg/kg i.m.) was lower in inner tl?an 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 sig nificant differences between laminar and turbulent flow? regions. The data indicate that free convection is the mechanism used by, the solut ion in pore penetration, although lack of understanding of this phenom enon at the cell level prevented conclusions fr om being drawn. Attemp ts to explain experimental variations revealed indications suggesting the influence of initial bulk density and initial wafer content on wat er loss and solid gain. (C) 1998 Elsevier Science Limited. All rights reserved.