# Physicochemical and Structural Properties of Freeze-Dried Lacto-Fermented Peach Snacks
## 3 Results and Discussion
### Hygroscopicity and Water Sorption Isotherms  
The water absorption properties of dried products from their surroundings were a very important characteristic. It affected their physical, chemical, and microbiological stability [34; 51]. The ability of freeze-dried peach samples to absorb water from the environment was evaluated using hygroscopicity measurements and water sorption isotherm analysis. These tests provided significant information on the behavior of products during storage, especially under conditions of increased relative humidity. Moisture sorption isotherms describe the sorption behavior of material stored in an environment of varying humidity [34; 52]. As illustrated in Figure 3, the data analysis revealed that all examined samples exhibited a characteristic type II sorption isotherm, commonly found in plant materials rich in sugars and fiber. An increase in relative humidity correlated with a notable rise in moisture content across all samples. However, clear distinctions emerged between the control sample (P)--freeze-dried peach without fermentation--and the fermented samples (P_LP and P_FF), which underwent lactic acid fermentation prior to freeze-drying. Specifically, the fermented samples exhibited a significantly lower moisture content, particularly at relative humidity levels above 50%. This reduction in water vapor sorption capacity suggested that lactic acid fermentation altered the sorption properties of peach tissue. These changes were likely due to structural and chemical modifications induced by the fermentation process, including osmotic effects. The use of a low-salt brine during fermentation may have led to salt migrating into the fruit tissue while soluble compounds such as sugars and polyphenols were released into the surrounding medium. These alterations may diminish the availability of hydrophilic binding sites or modify the architecture of the cell wall, thereby restricting moisture uptake at elevated humidity levels [23]. This phenomenon can enhance the stability of freeze-dried fermented products in high humidity, reducing hygroscopicity and lowering the risk of moisture-related degradation. This helps extend shelf life and maintain product quality. The significant differences between the variants indicated that the fermentation process significantly affected the sorption properties. The fermented samples (P_LP and P_FF)  
Figure 3: Water vapor adsorption isotherms in freeze-dried and fermented peaches. P—freeze-dried peach sample; P_LP—fermented with _Lactiplantiobacillus plantarum_ and freeze-dried peach samples; P_FF—fermented with _Fructilactobacillus fructivorans_ and freeze-dried peach sample. showed higher water sorption capacity than the control sample (P). Specifically, the P_FF sample absorbed the highest amounts of water, which may be related to its more porous structure (Table 2) and higher pore connectivity, which facilitated water penetration and accumulation. This was also confirmed by the results of pore size distribution (Figure 2), which showed a higher proportion of large pores in fermented samples. The results of the hygroscopicity test (Figure 4) also showed significant differences between the samples. After 72 h of exposure in an atmosphere with constant relative humidity (RH = 75), all samples showed an increase in water content, with the dynamics of this process being highest in the first hours (1-8 h) and then slowing down, reaching a plateau after about 24 h. The highest moisture gain was recorded for the P_FF sample, slightly lower for P_LP, while the control sample absorbed the least water. This may be due to the compact structure and lower porosity of the control sample (67.74%). The increased hygroscopicity of fermented samples may be directly related to transformations occurring during fermentation, such as the breakdown of pectins and hemicelluloses or the synthesis of hydrophilic compounds (e.g., organic acids) that increase water-binding capacity [53].