14A-7

G. MAZZANTI¹, C. Fernandez², and M. Le Maguer². (1) School of Engineering, University of Guelph, Guelph, ON N1G 2W1, Canada, (2) Department of Food Science

Treatment of fruits and vegetables by osmotic dehydration has been modeled in a number of microscopic and macroscopic ways. The kinetics of water loss and solids gain results from a complex interaction between the mass transfer process and the nature of the plant material. Research is needed to provide models that integrate the internal and external observations.

The objective of the study was to develop a model for the kinetics of osmotic dehydration of apples. The model should be based not only on the internal structural parameters of the tissue but also on the diffusion characteristics of the osmotic solution.

Samples of apple rings were subjected to osmotic treatment using 60% (w/w) sucrose solution. Samples were taken at different treatment times from 5 to 90 minutes. Cylindrical samples were taken from the rings and sliced at a certain thickness. These were used in assaying moisture and sucrose to determine the advance of the penetration front. Water loss was determined from moisture content measurements. Solids gain was calculated from sucrose content measured using high-performance liquid chromatography. The initial molecular weight of soluble solids was determined by osmometry. A conceptual and mathematical model was developed to relate the penetration and shrinkage with the water loss and solids gain evolution. The model was also tested against literature data.

The parameters for diffusional porosity, tortuosity, and average concentration were estimated by fitting the model to the data. As expected, a nonlinear relationship was found between these parameters and the shrinkage ratio.

This attempt to correlate internal and external data from osmotic dehydration processes pointed out specific experimental and conceptual needs for future research. These include data on the mechanical properties of the tissue; dimensional evaluations; initial properties of the material; and on the relationship between solutes and water fluxes.