## 3 Results and Discussion  
### Water Content and Water Activity of Snacks  
Water is an important component of food products inasmuch as the amount of water in food is crucial for its storage stability and physical properties. In fresh fruit and vegetables, water constitutes 77 to 96% of the total mass [20; 21]. In the case of the puree, which was the base of the snacks, the water content ranged from 84.9 \(\pm\) 0.1% to 88.6 \(\pm\) 0.1%, while the dry matter content ranged from 11.4 \(\pm\) 0.1% to 15.1 \(\pm\) 0.1%, depending on the puree formulation. The water contents of fresh formulations A, B, and C were 88.6 \(\pm\) 0.1, 85.5 \(\pm\) 0.1, and 84.9 \(\pm\) 0.1%, respectively.  
One of the parameters determining the state of water in food is water activity (a\({}_{w}\)). Water activity largely determines the course of biological, chemical, and physical processes; therefore, it is an important parameter when designing new products [22]. The oxidation of fats and fat-soluble substances takes place even at very low values of a\({}_{w}\), and the greatest slowdown of this reaction is observed at a\({}_{w}\) from 0.1 to 0.3. In turn, the rate of the oxidation of fat-soluble substances, such as chlorophylls, vitamin C, or anthocyanins, is proportional to the increase in water activity. The reactions of non-enzymatic browning, which cause unfavorable modifications of the color or smell and increase the hardness of the product, require a sufficiently high proportion of water in the environment. Their highest intensity is noted at a\({}_{w}\) from 0.3 to 0.7. In addition, it is assumed that food is the most stable in terms of physical changes (associated with unfavorable changes in texture) when its water activity corresponds to the share of water in the monolayer [23]. The water activity is also used to assess the microbiological safety of the product. It is assumed that most bacteria do not grow below a\({}_{w}\) of 0.9, yeast below a\({}_{w}\) = 0.8, and mold below a\({}_{w}\) = 0.7 [21].  
The water content and water activity of the differently formulated and prepared snacks are shown in Figures 2 and 3, respectively. In each of the snack flavor variants, significant differences were observed in the obtained water content (Figure 2) and water activity levels (Figure 3), depending on the drying method used.  
The hot-air-dried snacks were characterized by a higher water content as well as water activity, indicating that the selected drying method and parameters had a decisive influence on the degree of water removal from the fresh material [24]. For example, in formulation A of the snack with strawberry, fennel, and lemon juice, the water activity was 0.221 \(\pm\) 0.001 in the case of freeze drying, while when hot-air drying was used, this value was equal to 0.423 \(\pm\) 0.003. The measured water content of the variant A snack was 6.3 \(\pm\) 0.2% and 10.8 \(\pm\) 0.3% for the freeze-dried and hot-air snacks, respectively. In any case, both drying methods have led each of the obtained snacks to a water activity below 0.6, so it can be concluded that the drying process ensured their durability and microbiological stability [25].  
Figure 3: Water activity of snacks based on undersized kiwifruit for the formulations (A–C): FD, freeze-dried snack; HA, hot-air-dried snack. The same letters given for each column are homogenous groups and indicate no significant differences (\(\alpha\) = 0.05) between considered samples. Bars in the figure represent standard deviations.  
Figure 2: Water content of snacks based on undersized kiwifruit for the formulations (A–C): FD, freeze-dried snack; HA, hot-air-dried snack. The same letters given for each column are homogenous groups and indicate no significant differences (\(\alpha\) = 0.05) between considered samples. Bars in the figure represent standard deviations.