58-4 |
Continuous flow microwave-osmotic combination drying of apple slices |
H. LI and H. S. RAMASWAMY. Dept. of Food Science & Agricultural Chemistry, McGill Univ., Macdonald Campus, 21111 Lakeshore Rd., Sainte-Anne-de-Bellevue, QC H9X 3V9, Canada Osmotic dehydration is a water removal process by immersion of a water-containing cellular solid in an aqueous solution (syrup or brine). Osmotic dehydration of foods has potential advantages for the food-processing industry. However, osmotic dehydration is relatively slow. Therefore, acceleration of mass transfer would be advantageous. It is hypothesized that microwave heating combined with osmotic dehydration will increase moisture loss and reduce solids gain and treatment time. The objective of this study was to demonstrating the usefulness of the combined microwave-osmotic drying of fruits to improve moisture loss, reduce solids gain, to improve overall drying rate. Mass transfer was quantitatively investigated during microwave assisted osmotic dehydration of apple variety Idared over a range of temperature (34-66C), microwave power (heating strength to cause 5-25C temperature difference) and concentration (34-63Brix) of osmotic solution. Effective diffusion coefficients of water as well as sucrose were estimated using Fick's unsteady state diffusion model. Results showed that moisture loss under microwave heating process was always higher than normal osmotic dehydration, while the solids gain was maintained stable at same time. Experimentally determined diffusivity values, based on Fickian model, increased two-fold for moisture loss and no change for solids gain. Multilinear analysis of the estimated effective diffusion coefficients of water and solute revealed that these values depend upon temperature, concentration of osmotic solution and microwave heating strength as well as the combined effect of temperature and concentration. The increase was attribute to the pumping effect of microwave heating, which facilitated the transport of water. These results suggested that the moisture transfer rate of osmotic dehydration was enhanced by microwave treatment. This technique can easily be adapted for both batch and continuous flow systems for enhancing osmotic dehydration process.
Session 58, Food Engineering: Transport processes and kinetics
|