Abstract: In order to obtain high drying rates and high-quality dried products, a heat pump dryer with cold air was applied
to dry fresh Toona sinensis, and the drying characteristics under different drying conditions were investigated. The drying
data were fitted to the Weibull distribution function and the drying process was analyzed by investigating the parameters
of the Weibull distribution function. The weighted comprehensive evaluation of Toona sinensis under different drying
conditions was carried out based on drying time, energy consumption, chlorophyll content, VC content and rehydration
ratio. The quality of cold air dried products obtained under the optimum drying conditions was evaluated by comparing with
hot air drying and freeze drying. Results showed that increased drying temperature and inlet velocity and reduced loading
thickness significantly (P < 0.05) reduced the cold air drying time of Toona sinensis, and the effect of different drying
conditions on drying time was in the decreasing order of temperature > inlet velocity > loading thickness. The Weibull
distribution function could accurately describe the change in water content of Toona sinensis during cold air drying (R2 > 0.9)
with a shape parameter less than 1. The whole drying process was falling-rate drying, and was mainly controlled by internal
moisture diffusion. The effective moisture diffusivity of Toona sinensis was in the range of (6.272–9.637) × 10－9 m2/s, and it
was influenced most significantly by drying temperature. The highest comprehensive score of cold air dried Toona sinensis
was obtained under the conditions: drying temperature of 20 ℃, loading thickness of 3.0 mm and inlet velocity of 2 m/s.
Compared with hot air drying, the quality of cold air dried products was closer to that of vacuum freeze dried products.

Key words: Toona sinensis, cold air drying, model, quality