## 3 Results and Discussion
### Antioxidant Activity of Snacks Based on Undersized Kiwifruit  
The antioxidant capacity evaluates the potential of the food products to fight against reactive species, such as free radicals [43]. Many studies have reported a noticeable positive correlation between the presence of phenolic compounds (polyphenols and phenolic acids) and the antioxidant capacity of fruits and vegetables, which, if consumed in a daily diet, may reduce the risk of several societal diseases. The beneficial effect of phytochemical compounds on the body is determined not only by their quantity but also by the presence of other compounds with which they interact and their location within the cellular matrix [44]. The phenolic compounds contained in plants are trapped in membranes and cell walls, so using processing methods such as freezing or applying high temperatures can cause their release and better bioavailability [45]. Scientific studies on the effect of high temperature on the content of polyphenols have yielded different results--some of them report the increased degradation of these compounds, while others indicate the opposite effect due to the release of these compounds and their easier availability [46; 47].  
The antioxidant capacity of the snacks based on undersized kiwifruit was expressed in IC\({}_{50}\) values using the DPPH radical (Figure 8). A lower value of this parameter indicates the higher antioxidant capacity of the sample.  
Generally, in most cases of the A snacks (with the exception of the A_t snack containing strawberry, fennel, and lemon juice with trehalose) and B, no significant changes in antioxidant activity were observed. The lack of statistical changes in the freeze-dried and hot-air-dried snacks, as well as those indicating the greater antioxidant capacity of the hot-air-dried snacks and the lack of statistical differences in freeze-dried and hot-air-dried snacks, may also be related to the phenomenon observed by [PERSON] et al. [48], who studied dried slices of Granny Smith apples. The apples were dried at three temperatures, 40, 60, and 80 \({}^{\circ}\)C, respectively, at different airflow velocities, i.e., 0.5, 1.0, and 1.5 m/s. The antioxidant capacity did not show any significant differences for the samples dried at 40 and 80 \({}^{\circ}\)C although different values of phenolic compounds were observed in these samples; this behavior was explained by the progressive occurrence of Maillard reactions and at the same time transformations, leading to the accumulation of antioxidant compounds in the food matrix.  
Statistically significant differences in antioxidant activity were noted for snack C (with spinach and fennel) depending on the method of drying. In all of the C snacks, the IC\({}_{50}\) value was much higher in the hot-air-dried samples, which means that the freeze-dried snacks were characterized by higher antioxidant activity. It was particularly visible in the snack with the addition of trehalose, wherein the freeze-dried version was characterized by the IC\({}_{50}\) value at the level of 0.79 \(\pm\) 0.07 mg d.m./mL, and the hot air dried, which had much lower antioxidant activity because there was only 2.24 \(\pm\) 0.01 mg d.m./mL. In addition, the results obtained for the hot-air-dried snacks in snacks C with the addition of sucrose and trehalose were significantly higher than the other samples, which indicates their poor antioxidant capacity. However, it can also be related to the extraction process, where not only antioxidants but also antagonistic compounds are transferred from the sample to the solvent, which may falsify the final result [9]. [PERSON] et al. [49] reported a higher retention of the antioxidant activity measured by using the DPPH method for Asian pear drying with freeze-drying instead of hot air drying at 50 \({}^{\circ}\)C for 420 min; this could probably be ascribed to the decreased degradation of the antioxidant compounds.