The Deff value was increased gradually to the maximum value
and then declined as the decrease of moisture content (db) at all the
drying conditions (Fig. 4). In the initial period of drying, water
molecule inside of jujube was transferred to the evaporation front
which was on the surface of material. Hence, liquid diffusion of moisture was the main mechanism of moisture transport
(Thuwapanichayanan et al. 2011). With the extension of drying
time, the evaporation front was shifted into inside, vapor diffusion
was the dominant mode of moisture diffusion, thus, the values of
Deff increased. At the final stage, the moisture content was lower
and lower, the vapor amount became less and less, Deff value
decreased correspondingly. The results also showed great agreement with the previous study in the literatures (Fang, Wang,
Hu, 2009; Karathanos et al. 1990).