Impact of process conditions and coatings on the dehydration efficiency and cellular structure of apple tissue during osmotic dehydration

The combined treatment of coating and osmotic dehydration to apples was carried out by using dextrose and sucrose as osmotic agents. Prior to osmotic dehydration, apple cubes were coated using two hydrophilic coating materials, sodium alginate and low methoxyl pectinate (LMP). The effect of process variables, including the concentration and temperature of the osmotic medium, on the performance ratio and dehydration efficiency index was studied. Higher performance ratio was found in the coated apples at high temperature of 55 degrees C. Better performance was obtained when sucrose was the osmotic agent as compared to dextrose. Better dehydration efficiency was found in the coated samples at higher temperatures than at low temperature. Among the two osmotic agents, sucrose, with larger molecular size, could provide higher dehydration efficiency compared to dextrose. SEM results revealed that the cellular structure of the coated apples was better maintained than that of the non-coated samples, when osmotically dehydrated by sucrose solution at 55 degrees C. This may be due to the fact that the coating materials could well prevent the solute uptake and maintain the cell wall structure of the apples. In addition, the coated apples osmotically dehydrated by dextrose solution showed collapse of the cell structure. (c) 2006 Elsevier Ltd. All rights reserved.