Abstract:

This research was performed to study the drying characteristics of ginger slices. Hot air drying was conducted
with different combinations of hot air temperature (60, 70 and 80 ℃), slice thickness (2, 4 and 6 mm) and air velocity (0.4, 0.8
and 1.2 m/s). Then moisture ratio (MR) and drying rate were compared under different drying conditions and modeled. The
results showed that the drying process was described as a rate-falling model. The MR of ginger slices declined faster with
increasing hot air temperature and velocity, but slower with an increase in slice thickness. The fitting of mathematical models
was conducted based on eight different thin layer models. It was found that the modified Page model was superior to other
models with an average R2 of 0.997 9, minimum χ2 of 0.000 4, and minimum RMSE of 0.012 2. The model was expressed
as MR = exp[－(kt)n], k = - 0.023 85 + 0.000 505T + 0.023 38V - 0.004 993L, n = 1.318 307 + 0.003 016 5T - 0.204 05V -
0.002 859L, where T is air temperature, V is air velocity, and L is slice thickness, showing excellent goodness-of-fit as
validated using experimental data. Effective moisture diffusion coefficient (Deff) of ginger slices varied from 1.763 × 10-8 to
1.054 × 10-7 m2/s, which was positively related to drying temperature, slice thickness and air velocity, and activation energy
was 35.23 kJ/mol (R2=0.948 0). At last, the color changes of ginger slices at different air temperatures were examined.

Key words: ginger slices, hot air drying, mathematical model, color aberration