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Microwave-osmotic dehydration (MWOD) under continuous medium flow is a new technique with good potential for quality optimization. It combines microwave heating with osmotic dehydration for enhancing moisture transfer rate in the osmotic dehydration process and product quality. This study was carried out to investigate the effects of continuous medium-flow MWOD of apple (Red Gala) cylinders in immersion (MWODI) and spray (MWODS) modes, as well as with conventional osmotic drying (COD) under similar continuous medium-flow (immersion, CODI, and spray CODS) modes. Two temperature-sugar concentration conditions with different contact times were employed to create 24 different test conditions for each of the four methods to test the differences between them. The process was monitored based on changes in moisture content, weight reduction, and solids gain. The results showed, in general, that the continuous medium-flow microwave-osmotic dehydration under spray mode (MWODS) considerably enhanced the moisture transfer rate from the fruit, leading to a significant increase of moisture loss. For example, at 50°C/50°Brix for 2 h, the moisture loss with MWODS was 34-94% higher than in other methods, whereas the solids gain was 16-46% lower than with the other methods. Overall, MWODS was far more effective than similar techniques in enhancing moisture loss and simultaneously restricting the solids gain. [ABSTRACT FROM AUTHOR]

Azuara and diffusion models were evaluated for describing the mass transfer kinetics of apple (Red Gala) cylinders during microwave-osmotic dehydration under continuous-flow medium-immersion (MWODI) and medium-spray (MWODS) conditions as well as immersion (CODI) and spray (CODS) conditions without the microwave heating. Two different sets of experiments were carried out with all four methods. In the first set, osmotic treatments were given at 50°C/50°Brix and 40°C/40°Brix with a solution flow rate of 2800 mL/min and fruit-to-solution ratio of 1:30. The treatment times ranged from 0 to 120 min. In the second set, the MWODS was extended to other conditions (40°C-50°Brix and 50°C-40°Brix). The equilibrium moisture loss and equilibrium solid gains required for the diffusion model were predicted using the Azuara model. Both models well fitted the experimental data for mass transfer kinetics (R2 > 0.92). Higher equilibrium moisture loss and lower solid gain were observed in samples treated with MWODS compared with other methods. The equilibrium moisture loss and solid gain under MWODS were related to solution concentration and solution temperature. The diffusion coefficients representing moisture loss (Dm) and solid gain (Ds) were computed from the diffusion model. The Dm values for were higher and Ds values were lower with MWODS as compared to the other methods. Dm and Ds were dependent on temperature and concentration of the osmotic solution. Half-drying time for moisture loss and solids gain were also computed to compare the different methods. These were inversely related to diffusivity values. Overall, the highest moisture loss and the lowest solids gain were observed in MWODS. [ABSTRACT FROM AUTHOR]