Mass transfer kinetics and optimisation of osmotic dehydration (OD) of fruits and vegetables with diverse structures were studied. Different concentrations of sucrose (20-60°Brix) and process times (0-24 h) were used. Magee's model was appropriate for predicting water loss (WL), while Azuara's model fitted well solids gain (SG) data and represented more accurately the evolution of the complete process close to equilibrium. Polynomial equations for each kinetic variable [WL, SG and weight reduction (WR) -for pumpkin, kiwi and pear] using multiple linear regression were fitted for a selected range of experimental data (30-240 min, 20-60°Brix). A complete solution algorithm for desirability function was coded in Matlab Ò 7.2 (Mathworks, Natick, MA, USA) with the aim to optimise osmotic dehydration process in terms of WL, SG and WR; optimal conditions were found for each fruit. Besides, an optimal common zone was identified for OD corresponding to process time from 114 to 240 min and sucrose concentration from 54 to 60°Brix.

The influence of vacuum time and solution concentration on mass transfer and mechanical properties of osmodehydrated melon cubes has been studied. Pulsed vacuum osmotic dehydration (PVOD) was carried out at 30°C for 4 h, using sucrose solutions (40, 50 or 60°Brix) and applying a vacuum pulse (100 mbar for 5, 10 or 15 min). Kinetics of water loss, solid gain and stress at rupture were analysed, as well as effective diffusivities using the hydrodynamic model. The increase in solution concentration favoured water removal, but no significant effect of vacuum time was observed. The use of less concentrated solutions coupled to the action of vacuum pulse resulted in greater solid uptake. Samples subjected to PVOD using 60°Brix sucrose solution presented greater water loss, lower sugar uptake and better maintenance of fresh fruit texture throughout the process. Diffusion coefficients estimated by the hydrodynamic model showed a good fit to the experimental data.

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The heat and mass transfer during the combined process of osmotic-microwave drying (OD-MWD) of fruits was studied theoretically and experimentally through modeling and numerical simulation. With the aim of describing the transport phenomena involved in the combined dehydration process, the mass and energy microscopic balances were set out. For the first step (OD), two models with different levels of complexity were proposed, an osmotic-diffusive and a countercurrent flow diffusive model. For MWD, the energy and mass balances were solved, using moistureand temperature-dependent properties; inner heat generation due to transformation of the electromagnetic energy was accounted for by using the approximation of Lambert's law. The numerical solution obtained from OD was incorporated as initial values for the simulation of MWD. The model validation was satisfactorily carried out in pears, both fresh and osmodehydrated for 2 h in sucrose solutions and then irradiated in a microwave oven at 500 W. From the results it was observed that a higher dehydration rate was reached during microwave drying when the fruits were pretreated with 40 and 60 Brix sucrose solution.

The influence of particle size (PZ) and processing temperature (PT) on quality attributes and processing time of pumpkin cubes packaged in glass jars were evaluated during their pasteurization. Secondorder polynomial models were developed for the following responses: texture retention (TR), total colour change (TCC) and heating time (HT), using multiple linear regression for a range of operating conditions (20-30 mm and 85-100°C for PZ and PT, respectively). A combination of the polynomial models with the methodology of desirability function was used for optimization of the pumpkin pasteurization process. The obtained optimal conditions were 20 mm and 100°C for PZ and PT, respectively; in order to obtain TR of 82.21%, TCC of 7.54 and HT of 44.97 min. However, these optimal conditions change to 100°C and 21 mm and the responses obtained are TR of 73.60%, TCC of 7.52 and HT of 39.66 min, when the processing time is prioritized.

Abstract. The mass and energy transfer during osmotic microwave drying (OD-MWD) process was studied theoretically by modeling and numerical simulation. With the aim to describe the transport phenomena that occurs during the combined dehydration process, the mass and energy microscopic balances were solved. An osmotic-diffusional model was used for osmotic dehydration (OD). On the other hand, the microwave drying (MWD) was modeled solving the mass and heat balances, using properties as function of temperature, moisture and soluble solids content. The obtained balances form highly coupled non-linear differential equations that were solved applying numerical methods. For osmotic dehydration, the mass balances formed coupled ordinary differential equations that were solved using the Fourth-order Runge Kutta method. In the case of microwave drying, the balances constituted partial differential equations, which were solved through Crank-Nicolson implicit finite differences method. The numerical methods were coded in Matlab 7.2 (Mathworks, Natick, MA). The developed mathematical model allows predict the temperature and moisture evolution through the combined dehydration process.Mathematical subject classification: Primary: 06B10; Secondary: 06D05.

The objective of this work was to analyze the relevant process conditions on osmotic dehydration of plums and to determine the diffusion coefficients related to this process. The influence of solution (type and concentration of solute, temperature, fruit/solution ratio) and process time on water loss, water content and solutes gain were studied. Process analysis was performed experimentally by means of a set of 16 duplicate tests and numerically by mathematical modeling of the unsteady-state mass transfer phenomena. Experiments were carried out with glucose and sorbitol solutions (40–60 % w/w), dehydrating plum pieces during 2 h at temperatures of 25 and 40ºC, with fruit/solution ratios of 1/4 and 1/10. For calculating effective diffusion coefficients, a novelty inverse-method was applied, the approximate shape of food-pieces was considered using Finite Elements Method. Calculated diffusion coefficients ranged from 1.13 × 10−09to 4.71 × 10−09m2s−1and 0.44 × 10−09to 3.46 × 10−09m2s−1, for water and solutes, respectively.