A Study of Kinetics and Some Resulting Physical Characteristics of Dates (Barhi variety) During Drying (Modeling and Experimental Validation)



Date palm (Phoenix dactylifera L.) with its delicious and nutritious bearing fruit (dates) is an important agricultural core in Iran. To extend the shelf life of date palm fruit, some such methods of preservation as drying are suggested and drying influences physicochemical and quality characteristics of products, thus modeling of drying kinetics is one of the tools for process control. In this research Barhi dates at khalal stage of maturity, after thawing, skinned and skinless, were dried in a laboratory scale hot-air dryer, under air flow of 1.5 m/s and air temperature of 60, 70 and 80 ?C. On the basis of these data, kinetics of the drying process were assessed and a characteristic drying curve established. The results showed that drying rate of skinless dates at 80 ?C is higher than that under other conditions. In plot of drying rate versus time, results indicated that drying took place in the falling rate period. The experimental data didn't show the dominating effect of temperature and being skin or not on the rehydration trend of this product. The influence of temperature and being skinned or not on the rehydration can thus be neglected. Results show that temperature and being skinned or not, have dominating effects on color index L,a and b Hunter Lab system. In order to estimate and select the appropriate drying kinetic model, the drying data as the moisture ratio (MR) versus drying time were fitted to a number 13 thin layer drying models. The comparison criteria employed were to evaluate goodness of fit, namely the coefficient of determination (R2), the root mean square error (RMSE) and the reduced chi-square (?2). The Wang model for drying of dates with skin and the Verma model for drying of skinless dates gave higher R2 vs. and lower RMSE and ?2 values than those in the other models.