The effect of osmo-convective dehydration on drying behavior and product quality of persimmon fruits

The aims of this study were to determine the mechanism of the osmotic dehydration in sucrose, glucose and maltose solutions and the effects of some factors including concentration and composition of solutions, temperature and agitation during osmotic dehydration of astringent persimmon. Besides, the effects of osmo-convective dehydration on drying behavior, sorption and quality features were investigated. According to the results obtained;The soluble solid content of the persimmons were increased due to temperature and osmosis time. The higher total dry matter contents were found high in the samples osmotically dried in sucrose solutions. After osmotic dehydration, the aw value of the samples were quite high to keep them from deterioration. Thus, the products were preserving by any conservation process after osmotic dehydration. Total phenolic matter contents of the samples were decreased in the ratio of 48.6% and 96% respectively, at the end of the osmotic process and convective dehydration. There were no differences between control and osmo-convective samples. The L*, a* and b* values of persimmons were changed significantly during osmo-convective dehydration. The bulk and real density of the osmosed samples were higher than the fresh persimmon. Porosity of the samples dehydrated in glucose solution following by convective drying was found higher. The conditions of osmotic process were not effective on shrinkage of persimmons. Rehydration capacity of osmo-convective dehydrated samples was found to be lower than the control samples.The water loss, weight reduction and solid gain were higher in the samples dehydrated at sucrose solution. Azuara et al. (1992) model was fitted best with the data in static conditions for water loss and agitated medium for solid gain.The sorption isotherms of all dehydrated persimmons were showed characteristics of type III isotherm. This type isotherm was observed for high sugar foods. The experimental data for all dehydrated persimmons were fitted well with GAB, Henderson and Halsey models. Osmotic dehydration processes were found to increase the isosteric heats of sorption according to control samples.