Abstract
Partially dehydrated tomato gels are innovative food products of extended shelf life for using in snack preparations. Flexible, sheet-shaped product was obtained by a pectic gelation mechanism induced by dehydration, starting from a formulation based on tomato puree. The drying kinetics of this product was studied in a bench-scale tray dryer operating between 40 and 80 °C at an air velocity of 2m/s. The `in-dryer' weighings of the trays allowed accurate experimental data to be recorded. The observed drying curves were modeled in two stages: for high moisture contents, with a constant drying rate model while at lower moistures, with an analytical-diffusive model, solved for the average sheet thickness. The mass-transfer Biot number in the diffusive model was found to be 1.1, indicating that external and internal resistances to mass-transfer are comparable. An Arrhenius model correctly described the temperature dependence of the water diffusion coefficient in the tomato pectic gel, represented by an activation energy of 22.0 kJ/mol. The model can be used to estimate minimum drying times and can be incorporated in tray dryer simulators for computer prototyping of new designs, and optimization of existing drying facilities.
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