EFFECT OF SHRINKAGE ON PREDICTION ACCURACY OF THE WATER DIFFUSION MODEL FOR PINEAPPLE DRYING

Drying kinetics of pineapple slabs was analyzed. Fruits were cut into 6-mm-thick slices and dried in a convective cross flow dryer at constant air velocity (1.5 m/s) and temperature (45, 60 or 75C). Two simple diffusional models were applied for modeling the mass transfer during pineapple drying. In the first model, fruit shrinkage was ignored and the analytical solution was applied. In the second model, the premise of variable shrinkage with moisture content was assumed, and the mass transfer equations were solved through a finite differences scheme. In addition, an empirical model of drying rate was found. The average error of moisture estimation was lower for the model with shrinkage. Moisture diffusivity values increased with temperature and decreased when shrinkage was taken into account. Results also showed that fruit shrinkage can be represented by a linear function of moisture content and that volume variation was independent of drying temperature. PRACTICAL APPLICATIONS Pineapple is one of the most popular tropical fruits and is consumed mainly as canned, juice or fresh fruit; a lesser proportion is consumed as dried fruit. However, the drying makes it possible to extend the shelf life of pineapple by reducing water content and improves efficiency in transportation and storage. In this study, characteristics of drying kinetics of pineapple slices at different air temperatures were studied. Also, a simple model for the simulation of drying process, taking into account the fruit shrinkage, was proposed. The results of this study will be helpful in the technological application of hot air drying for pineapple preservation.