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  • Author or Editor: A.M.M.B. Morais x
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Effects of the osmotic pre-treatment (OD) with sucrose or sorbitol solutions and different drying methods on the rehydration kinetics of apple cubes were studied. Samples were dried by hot air (HAD) at 70 ºC, by microwave (MWD) at 500 W, and by freeze-drying (FD). The rehydration of dried samples was performed in water at 80 ºC and at a mass ratio of sample to water of 1:100. The first order kinetic model was found to provide the best fit of the rehydration data. The pre-treatment and the drying method did not affect the rehydration kinetics, but the rehydration capacity after 12 min of rehydration was higher in the control samples than in the osmotically dehydrated ones, for all three drying methods. The rehydration rate and the rehydration capacity of the apple cubes dried by HAD, MWD, or FD were not affected by the solute used in the pre-treatment, sucrose and sorbitol.

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Apple cubes were osmotically dehydrated with 40 °Bx sucrose and sorbitol solutions. Light microscopy was used to observe the microstructure of fresh and osmotically dehydrated samples. Peleg’s model could fit the experimental data and describe the mass transfer kinetics of water loss (WL) and solid gain (SG). The use the sorbitol as osmotic agent, the increase of temperature and concentration of the solution increased the WL during the osmotic dehydration. The average cellular parameters, area and perimeter (size), and circularity, elongation, roundness, and compactness (shape) of fresh samples were 14.28±6.65×103 μm2 and 0.486 mm, and 0.73, 1.56, 0.70, 0.83, respectively. The osmotically dehydrated samples presented a decrease in area, circularity, roundness and compactness and an increase in the elongation of the cells, and these changes were higher in samples treated with sorbitol.

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