## 3 Results and Discussion
### Color
PEF could also  
Figure 3: Values of the L* color parameter of dried apples depending on the various process parameters (distance between the infrared lamps and the apple slices during infrared–convective drying, IR-CD: 10, 20, and 30 cm; specific energy input during pulsed electric fields pretreatment, PEF: 0, 1, 3.5, and 6 kJ/kg); the uppercase letter (A) represent homogeneous group in terms of distance, but the lowercase letters (a–c) indicate homogeneous groups in terms of specific energy input (\(\alpha\) = 0.05). promote enzymatic browning of treated apples due to potentially boosting polyphenol oxidase or peroxidase activity [7; 19; 25; 34; 35]. Moreover, milder-processed apples (1 kJ/kg) were significantly redder after drying than apples with the highest specific energy input (6 kJ/kg). The last coordinate in the CIELab color space is b*, which indicates yellow (positive) and blue (negative) opponents [36]. For fresh apples, b* took a value of 17.7 \(\pm\) 1.9, while for all dried samples, values of that color parameter were in the range of 21.1-25.5. The b* color parameter was significantly dependent only on the distance between the infrared lamps and the apple slices (\(\eta^{2}\) = 0.137). As can be seen in Figure 5, the shortest distance between the apple slices and the infrared lamps during drying (10 cm) resulted in products with significantly higher yellowness (in relation to the distances of 20 and 30 cm). Similarly to the previous color parameter in the CIELab color space (a*), the increase in the yellowness of the material exposed to elevated temperature could be related to the Maillard reaction and caramelization process [27; 32; 33]. It is worth mentioning that the application of the pulsed electric fields did not have a negative impact on the color of dried apples in terms of their yellowness. Similar conclusions were drawn by other authors in studies conducted on hot-air-dried carrots [37] and purple potatoes [38]. Moreover, apples supplied with 3.5 kJ/kg energy before IR-CD exhibited significantly lower values of the b* color parameter after drying than the untreated ones. Based on the obtained values of L*, a*, and b* color parameters, the total color difference (\(\Delta\)E) was calculated with reference to the fresh apple. This parameter allows for the assessing of the color deviation of a given material (in this case dried apples) from a particular standard (fresh apple) [39]. For all dried samples, it took values in the range of 7.8-20.5. It means that the differences in color between raw material and final dried products were clearly visible [40]. \(\Delta\)E was significantly influenced not only by the distance between the infrared lamps and the apple slices (\(\eta^{2}\) = 0.146) and the specific energy input (\(\eta^{2}\) = 0.637) but also by the interaction of these two independent variables (\(\eta^{2}\) = 0.249). As can be seen from Figure 6, IR-CD carried out at the shortest distance between the material and the infrared lamps (10 cm) resulted in obtaining dried apples with the highest total  
Figure 4: Values of the a* color parameter of dried apples depending on the various process parameters (distance between the infrared lamps and the apple slices during infrared–convective drying, IR-CD: 10, 20, and 30 cm; specific energy input during pulsed electric fields pretreatment, PEF: 0, 1, 3.5, and 6 kJ/kg); the uppercase letters (A–B) represent homogeneous groups in terms of distance, but the lowercase letters (a–c) indicate homogeneous groups in terms of specific energy input (\(\alpha\) = 0.05). color difference (in relation to processes performed at the distance of 20 and 30 cm). As mentioned above, a shorter distance from the heat source means higher heating of the apple's surface, which could promote browning reactions [27; 32; 33]. Application of PEF as a pretreatment before IR-CD resulted in obtaining dried products with a higher total color difference from the raw material than untreated samples.