Convective drying of cherry tomato: Study of skin effect

A whole single cherry tomato is dried in a forced convective micro-dryer. The experiments are carried out under temperatures of 50, 60, 70 °C and a constant air flow and humidity. In order to study the effect of the skin two sets of experiments were performed using original tomatoes or after skin was handly removed. The drying kinetics show the existence of two main phases, which are: adaptation phase and falling drying rate phase with an increase of the drying rate with the temperature increase. The observation of the product behavior shows that shrinkage effect is largely happening during the process. It is possible to follow this effect represented by variation of the product volume with its moisture content using X-ray microtomography. This non destructive imaging technique has been proved to find interesting applications in the drying field.
In a second part, mathematical modeling using diffusion equation based on Fick’s law is studied. Consequently and using the analytical solutions proposed by Crank (1975), the diffusion coefficient is determined and written as function of the drying air temperature under Arrhenius form permitting by this way the calculus of the activation energy. The skin effect is clearly determined as the calculated diffusion coefficient of an original tomato with skin is largely smaller than the one without skin.