# Effect of PEF Treatment on Chosen Properties of Raw and Hot Air- and Freeze-Dried Poultry Meat
## 3 Results and Discussion  
The influence of pretreatment on the kinetics of the hot air- (HA) and freeze-drying (FD) processes of poultry meat was studied. Figure 1 shows the drying curves recorded within the time of the hot air- and freeze-drying of the poultry meat that was and was not subjected to the PEF pretreatment. Additionally, Figure 2 presents the drying time of intact and PEF-treated poultry meat dried with hot air and freeze-drying to moisture ratio (MR) equal 0.20 and MR = 0.04. Presented curves on Figure 1 demonstrate that both processes were the most intense in the beginning and progressively slowed down as the moisture ratio decreased. The PEF pretreatment affected the course of the water removal in opposite ways regarding different drying methods. In the case of the traditional drying at 60 \({}^{\circ}\)C, the application of the PEF slowed down the dynamics of dehydration compared to the untreated sample. That observation was unexpected, considering that in meat processing, the PEF is used as a factor that loosens the structure of the material to make it softer and more tender, thus usually improving mass transfer [42]. Nevertheless, the results obtained in this research suggest that the broken structure of the material could have collapsed and trapped contained moisture inside the sample, reducing its mobility. Another possible explanation may be related to the PEF improving the gelling properties of meat-origin protein [43], which could cause water holding and crust formation that led to slower moisture release. Additionally, elevated water-holding properties were also observed during thawing of the meat subjected to the PEF treatment, which resulted in significantly reduced leakage [44]. On the other hand, the freeze-drying process was improved after the PEF application in the process efficiency and lower equilibrium moisture ratio. Electroporation, which destroyed the cells building the dried tissue, followed by its preservation due to freezing, allowed the vapor to effectively migrate from the material without damaging its structure and shape [45]. Thanks to the low shrinkage and shape maintenance, freeze-dried materials are remarkably porous, and that increased porosity (see Figure 3) may be considered one of the crucial parameters enhancing mass transfer during drying, due to the open structure that is no longer a barrier. The improvement in the freeze-drying of samples subjected to a PEF may be also related to the formation of a large number of ice nucleation centres during freezing, resulting from the phenomena of electroporation and perforation of the cell membranes [46]. However, the pretreatment application notably changed the shape of the drying curves. Statistical analysis indicated that the PEF treatment did not affect the drying time needed to reach a moisture ratio at the level of 0.2 (Figure 2, on Figure 1 mark with red line). The reduction of the relative water content to a value of 0.2 or below is necessary for the production of meat snacks known as \"jerky\" [47]. Nevertheless, drying time measured until the material's moisture ratio decreased to 0.04 shows the impact of the PEF pretreatment. During hot air-drying, only the highest energy intake (30 kJ/kg) caused a significant prolongation of the drying time by 68%, while treatment with lower parameters did not influence the final drying time. In the case of freeze-drying, the time of the process was significantly shortened after the PEF treatment. The dehydration through sublimation was 50% faster in the PEF-treated poultry meat, regardless of the parameters applied to the intact sample. The results obtained for hot air-drying are not consistent with previous findings. For example, [PERSON] et al. [48] proved that the combination of HA at 60 \({}^{\circ}\)C with a PEF in chicken breast processing allows for a significant reduction in drying time and energy consumption of this type of processing.