## 3 Results and Discussion
### Convective and Infrared Drying  
#### 3.1.1 Kinetics and Drying Time of Terebinth  
Figure 1 shows the results for various dryers (CV at temperature 50-70 \({}^{\circ}\)C and IR with infrared power of 250, 500, and 750 W) as well as different pretreatments (US, MW, and BL) on drying treebinth. The longest drying time (345 min) was obtained for the convective dryer working at a temperature of 50 \({}^{\circ}\)C in the case of control samples, while for IR dryer operating at 250 W for controls was 275 min. At the beginning of the drying, a sharp descending kinetics slope in the initial drying steps was observed, which got milder in the next stages. The reason could be high moisture diffusion in the initial steps of the drying. As time passed, the moisture content of the product was declined and the moisture diffusion was decremented which reduced the drying rate in the treebinth layers, hence prolonging the drying time which can be observed in the final stages of the drying [6]. A comparison of Figure 1a,b shows that the drying time was declined by enhancing the temperature due to the increased movement of the water molecules in the product as a result of heat which accelerated the evaporation. Moreover, a rise in the temperature enhanced the moisture transfer rate to the surface, thus accelerating the evaporation. Therefore, the drying rate will be incremented at high temperatures [30]. Similar results were also reported by [PERSON] et al. [13], [PERSON] et al. [22], and [PERSON] et al. [5] for drying pear slices, green pea, and lemon, respectively. It can also be observed that in the IR dryer, with increasing the power, the slope of the moisture ratio was incremented, thus reducing the drying time. A rise in the IR power increased the dryer temperature. On the other hand, it enhanced the moisture absorption capacity of the air due to the increase in temperature difference between the air and the product which accelerated the product heating resulting in better water evaporation and shortening the drying time [31]. The results can be compared with the findings of [PERSON] et al. [32] in drying eggplant slices and [PERSON] et al. [4] in drying strawberries. According to Figure 1a-c, the use of pretreatment (in both dryers) reduced the drying time in the range of 3.6 to 51.4% in comparison to samples without pretreatments. In pre-treated samples, the change in the rate of moisture transfer from the center of the sample to the surface increased. By examining the effect of different pretreatments at various temperatures for CV drying and powers for IR drying, it can be found that MW pretreatment can reduce drying time more than the other two pretreatments (US and BL). MV pretreatment reduced the drying time in the range of 33.3-51.4% for CV drying and 41.8-50% for IR drying when compared to the samples dried without pretreatment at various temperatures and powers, while for BL and US applied before CV drying the reduction was in the range of 13.0-16.7% and 5.4-11.1%, respectively. For IR drying the BL and US treatment resulted in a decrease of drying in the range of 7.3-21.3% and 3.6-14.3%, respectively. This may be because the microwave pretreatment destroyed the surface of the treebinth making its pores larger, hence, the humidity can quickly leave the surface. Similar results have been reported in drying turnips [33]. Comparison of the results indicated that the blanching pretreatment shortened the drying time more than US pretreatment. Blanching treatment inactivates the enzymes and removes oxygen from the intercellular spaces, and as a result, the mass transfer occurred faster in these samples [34]. Similar