## 3 Results and Discussion
### Properties of Convective and Infrared Dried Terephthal  
#### 3.2.1 Effect of Pretreatments (US, BL, MW)  
Applied before Convective and Infrared Drying on Color of Terephthal  
Color is one of the key factors, which is important for consumers [27; 40]. Figure 2 shows the effect of temperature in CV drying, IR power in IR drying, and pretreatment method on the total color difference (\(\Delta\)E). The highest \(\Delta\)E (26.26) is related to the power of 250 W in the control sample. The IR method with MW pretreatment (compared to other pretreatments) exhibited the highest amount and rate of color changes. In this method, although the samples are placed in the dryer for a short time, the drying temperature used is so high that the non-enzymatic browning reaction is performed at high intensity resulting in the color changes [38]. The speed and intensity of color changes are much higher in drying with MW pretreatment. As microwave heating is non-uniform, the samples may burn during the process, leading to higher color changes in this pretreatment compared to the others. [PERSON] et al. [41] investigated the effect of microwave power and ultrasound on red beetroot drying and they indicated that high volume heating by the microwave cause high internal pressure inside the samples, which enhanced the color changes. In all of the studied methods, the total color difference of the samples altered over time, although in some methods, the intensity of the changes was very high. The \(\Delta\)E higher than 5 means the noticeable color change for the non-trained observer [27]. Thus the best case was when the \(\Delta\)E was very low. The type of drying and pre-treatment can strongly affect the total color difference. According to Figure 2, the lowest color change (14.25), but still higher than 5, is related to CV drying at a temperature of 60 \({}^{\circ}\)C and the use of US pretreatment. This is because the process temperature is lower in these methods compared to the infrared methods, resulting in a lower Millard reaction intensity. Therefore, the samples dried by these methods had much better quality in terms of the color [42]. These results were consistent with the reports of [PERSON] et al. [31]. The total color difference decreased with increasing air temperature from 50 to 60 \({}^{\circ}\)C and infrared power from 250 to 500 W. One of the reasons is that low temperatures affect the properties of nutrients due to prolonging the drying time, hence, increasing the color changes of terephthal at low temperatures. Furthermore, with increasing temperature from 60 to 70 \({}^{\circ}\)C and infrared power from 500 to 750 W, because of the high temperature decomposes the pigment and enzymatic reactions are inhibited, while non-enzymatic browning reactions increment the color changes [43]. 2.2 Effect of Pretreatments (US, BL, MW) Applied before Convective and Infrared Drying on Rehydration Rate (RR) of Terebinth  
The rehydration properties of the dried material are very important [26]. Based on Table 2, the final rehydration rate of the samples dried by CV and IR with various pretreatments was statistically significant at 5%. According to Figure 3, the highest rehydration rate (3.17) was for the samples dried using a CV dryer at a temperature of 60 \({}^{\circ}\)C upon using US pretreatment. In this method, the water capacity was significantly higher at 60 \({}^{\circ}\)C when compared with 50 and 70 \({}^{\circ}\)C. This implies that the structural changes that destroyed the hydrophilic character of the samples were higher at 50 and 70 \({}^{\circ}\)C. These results are in line with the works of [PERSON] et al. [44] on pomegranate. Figure 3: Effect of different pretreatments (Untr: control, US: ultrasonic, BL: blanching, MW: microwave) and different conditions of drying methods temperature (50, 60, and 70 \({}^{\circ}\)C) for CV drying and infrared power (250, 500, and 750 W) on rehydration rate (RR) of dried tereinth.