# Physicochemical and Structural Properties of Freeze-Dried Lacto-Fermented Peach Snacks
## 3 Results and Discussion
### Microstructure and Texture of Freeze-Dried Peaches  
According to [PERSON] and [PERSON] [34], consumers prioritize color and structure-texture properties when evaluating foods. Structure-texture porosity is an important and characteristic feature of freeze-dried food, closely related to its physicochemical changes [35]. A comprehensive evaluation of the internal structure and texture of freeze-dried peach samples was carried out using light microscopy (LM), scanning electron microscopy (SEM), and X-ray microtomography (uCT). The imaging techniques allowed visualization of the structural changes induced by lactic acid fermentation and the subsequent freeze-drying process. As shown in Figure 1 (light microscope--LM), the peach freeze-dried sample (P), which had not undergone fermentation, showed a relatively compact and homogeneous structure on both light microscopy and SEM. The tissue appeared dense, with minimal damage to the crumb cells and a limited number of pores. In contrast, samples fermented with _Lactiplantibacillus plantarum_ (P_LP) and _Fructilactobacillus fractivonans_ (P_FF) showed significant structural loosening. SEM images revealed intense cellular damage and the presence of larger, irregular voids. uCT scanning further confirmed these changes, showing increased porosity and more heterogeneous internal structure in the fermented samples. In a study by [PERSON] et al. [36] and fermented chili peppers, it was noted that after fermentation, the tissue of the peppers loosened significantly, and the texture softened. The quantitative data from the microtomographic analysis confirmed a notable increase in porosity and a significant reduction in Euler number following fermentation (Table 2). Compared with the control sample (67.7%), porosity increased by approximately 5.3% in the P_LP sample and by 7.4% in the P_FF sample. At the same time, the Euler number decreased markedly, indicating a more complex and interconnected pore structure. Specifically, the Euler number dropped by 51.7% in P_LP (from \(-\)411,032 to \(-\)623,697) and by 102.5% in P_FF (to \(-\)832,126), demonstrating the strong impact of fermentation on internal microstructural connectivity. [PERSON] et al. [37] described changes occurring in the cell wall morphology and mechanical properties of purfing dried peach slices. They showed that the process of treating the fruit caused uneven distribution of pores in the cells, which simultaneously led to changes in \begin{table}
\begin{tabular}{c c c c} \hline
**Sample Code** & **P** & **P\_LP** & **P\_FF** \\ \hline Porosity (\%) & 67.74 \(\pm\) 3.48 a & 71.36 \(\pm\) 2.48 b & 72.77 \(\pm\) 1.93 b \\ \hline Euler number (-) & \(-\)411,032 \(\pm\) 69,149 b & \(-\)623,697 \(\pm\) 37,049 ab & \(-\)832,126 \(\pm\) 86,835 a \\ \hline Hardness (N) & 50.1 \(\pm\) 15.2 b & 35.72 \(\pm\) 12.7 a & 28.2 \(\pm\) 10.1 a \\ \hline \end{tabular} a, b—results marked in rows with the same lowercase letters are not statistically significantly different at \(\alpha\) = 0.05.  
\end{table} 
Table 2: Structural and mechanical properties of peach samples. Figure 1: Internal morphology; LM—light microscope; SEM—scanning electron microscope (magnification \(\times\)150); \(\mu\)CT—micro-tomography; P—freeze-dried peach sample; P_LP—fermented with _Laciplanitiobacillus plantarum_ and freeze-dried peach samples; P_FF—fermented with _Fruticilatobacillus fructrotrans_ and freeze-dried peach sample. the mechanical properties of the products. The process carried out at high temperatures also caused cell wall destruction, formation of new pores, and cellulose degradation. [PERSON] et al. [38] obtained increased porosity of apples after blenching and freeze-drying processes. On the other hand, in a study by [PERSON] et al. [39], the microstructure of dried pear slices showed that it was the products obtained by freeze-drying that had the highest pore diameter and spongy texture. Plant products' texture strongly correlates with the integration of the cell wall of the raw tissue [40].