AIR-DRYING OF FRESH AND OSMOTICALLY PRE-TREATED PINEAPPLE SLICES: FIXED AIR TEMPERATURE VERSUS FIXED SLICE TEMPERATURE DRYING KINETICS

Abstract

In this investigation, the air drying characteristics of fresh and osmotically pre-treated pineapple slices in a tray dryer were studied under different operating conditions. The air velocity varied from 1.5 to 2.5 m/s and the air temperature from 40 to 70°C. The analytical solution of the second Fick's law for an infinite slab was used to calculate effective diffusion coefficients and their temperature dependence could be well represented by an Arrhenius-type equation. Comparison of the results showed that the diffusion coefficients were lower for the pre-treated fruit. By means of automatic control, it was possible to obtain drying curves under conditions of constant product temperature, which showed to be an alternative to reduce the drying time of pineapple slices.

Keywords:

• Activation energy
• Automatic control
• Drying rates
• Effective diffusivity

ACKNOWLEDGMENTS

Authors acknowledge the financial support received from FAPESP (São Paulo State Research Fund), Procs. 98/05130-8 and 99/01255-3, and CNPq (Brazilian National Council for Research and Development), Proc. 300956/97-5, and the technical assistance received from SMAR Equipamentos Industriais Ltda.