## 4 Discussion  
Epidemiological studies clearly indicate that the diet plays a significant role in the prevention of many chronic diseases [41]. Fruit yogurts have become a popular product in the diet of many people, but their high content of added sugars is controversial. Excessive consumption of products with a high content of sugars not only increases the calorific value of the product, but may also contribute to the development of obesity and its complications [42]. An alternative could be the consumption of natural yogurt (without added sugars), although its flavor profile may make it less appealing to some consumers. Natural yogurt with the addition of fresh or thawed fruit may be a better alternative to commercial fruit yogurts. We decided to investigate whether the amount and type of relatively unprocessed fruit (frozen) has an impact on the antioxidant activity of yogurts. Natural yogurt with fruit without added sugar can be a much healthier option. These products contain only naturally occurring sugars from the fruit, which help preserve the desirable flavor without adding excessive calories [43]. Differences in antioxidant compounds, such as solubility, ability to form hydrogen bonds, and ionic conditions, can affect the results obtained from methods used to assess antioxidant activity [35]. Various methods, including ABTS and DPPH assays, can be used to determine the antioxidant activity of yogurts. It should be noted that the methods used differ in their conditions, such as sample incubation time and solution concentration [44]. When analyzing DPPH radical scavenging activity, all natural yogurts with the addition of different fruits showed higher antioxidant capacity compared to commercial yogurts, which was not always confirmed by the ABTS method (Table 4). Each method has its limitations; for example, the Folin-Ciocalteu assay, often applied to measure total phenolic content, can be influenced by the presence of some amino acids, vitamins and their derivatives (e.g., ascorbic acid), and inorganic reducing ions [45]. Although the majority of the recorded results are likely affected by the phenolic content, for clarity of message, in this study, we used the term \"total reducing capacity\". To avoid bias, we employed different methods. While none of these methods is perfect, we assumed that statistically significant differences between samples would allow us to identify, among fruit yogurts, those with higher nutritional value. An interesting phenomenon can be observed when comparing Table 3 with Table 4: yogurts with added strawberry (DS) generally showed lower values for ABTS, DPPH, and RP compared to the selected commercial natural yogurt. There are several possible explanations for this observation. \begin{table}
\begin{tabular}{c c c} \hline \hline  & \multicolumn{3}{c}{**Number of Bacteria [log CFU/g]**} \\ \hline
**Yogurt** & _Lactobacillus_ & _Streptococcus_ \\ \hline Cornelian cherry & 8.1  & 10.5  \\ Strawberry & 8.4  & 10.3  \\ Bilberry & 8.5  & 10.6  \\ Cherry & 8.6  & 10.7  \\ Natural & 9.0  & 10.3  \\ \hline \hline \end{tabular} a-b Values are means; means with different letters for the same bacteria strain are significantly different (\(p\leq 0.05\)).  
\end{table} 
Table 8: The number of _Lactobacillus_ and _Streptococcus thermophilus_ cells in yogurts with the addition of 10% of fruits. First, plant-based antioxidants (e.g., polyphenols, flavonoids) can form complexes with milk proteins (e.g., casein), which reduces their availability and reactivity in antioxidant tests such as DPPH and ABTS. For example, [PERSON] et al. [46] observed that the antioxidant capacity of several green and black tea components with \(\alpha\)-, \(\beta\)- and \(\kappa\)-casein or albumin is not additive; that is, part of the total antioxidant capacity is masked due to these interactions. This masking effect depends on both the protein and the flavonoid involved. Similarly, the study by [PERSON] et al.