Drying kinetics model and physical properties of herb Pandanus leaf

The objectives of this research were to study drying kinetic of Pandanus leaf for herbal tea by hot air (HA) convection, infrared (IR) radiation and combined HA and IR heat sources (HA+IR). The thin-layer drying kinetics equation of Pandanus leaf was mathematical simulated for all three drying strategies. Determination of physical quality and specific energy consumption (SEC) were carried on. The experiments were carried out under the conditions of infrared radiation power of 1,000 W and drying temperature ranges between 45 and 65°C. The hot air flow rate was fixed at 1.0-1.2 m/s. Initial moisture content of Pandanus leaf was range of 400 to 600% dry-basis and the final moisture content was between 8 and 12% dry-basis. The experimental results showed that the drying rate using combined HA+IR was faster than drying using HA and IR, respectively. The simulated data using empirical Logarithmic model for all heating methods had a good relation to the experimental data. According to the liquid diffusion following Fick's law, the effective diffusion coefficient was depended on drying temperature and drying method. Evaluation of SEC showed that SEC of IR drying was lower than drying with HA and combined HA+IR, respectively. The SEC with all three heat sources was in ranges of 8.33-17.70 MJ/kg.H₂O evaporated. The SEC is decreased with increase of drying temperature. For product quality analysis, percentage of rehydration and the colorness value (CIE lab) of dried using HA, IR and combined HA+IR are significantly different (p≤0.05).