## 3 Results
The highest values of the antioxidant parameters measured by the DPPH method and the reduction power (RP) were recorded for N, N4 and N6, with N6 also showing the highest ABTS value among them. Based on these results, yogurt N6 was selected for the preparation of fruit-enriched yogurts. Fruit contents ranging from 3% to 13% were selected to approximate the fruit levels found in commercial yogurts, while a 20% addition was included to create a strongly fruity yogurt and to assess how such a high fruit level influenced the antioxidant properties of the diet yogurts. As shown in Table 4, the values of DPPH, ABTS reduction power and phenolic compounds varied depending on the fruit content in the yogurts. The highest antiradical activities measured by the ABTS method were observed in diet yogurts containing 20% bilberries and comelian cherry, whereas the lowest values were recorded for most commercial strawberry yogurts (Table 4). The lowest ability to neutralize free radicals and the lowest reduction power were observed in yogurts with lower fruit content. On the other hand, the content of phenolic compounds was higher in commercial fruit yogurts (strawberry, bilberry, cherry) than in the corresponding diet yogurts. Analyzing the antioxidant activity of diet fruit yogurts, we note that TRC ranged from 0.66 mg GAE/mL (commercial strawberry yogurt) to 0.98 mg GAE/mL (commercial bilberry yogurt). Among the diet yogurts, the samples with 20% additions of comelian cherry and bilberries, DD (20) and DB (20), respectively, had the highest phenolic content. The antioxidant activity of yogurts with cornelian cherry, cherry, and strawberry, as measured by the DPPH method, did not differ significantly between samples. However, an increase in the addition of comelian cherry was associated with a consistent rise in antioxidant activity (as measured by ABTS), reduction power and phenolic content. Since the detailed analysis presented in Table 4 may be difficult to interpret unambiguously, several simplifications have been made for statistical purposes. Specifically, values for each level of fruit addition (Table 5) were calculated. The results showed that increasing the amount of fruit in diet yogurts significantly enhanced the antioxidant activity, as measured by both the DPPH and ABTS methods, as well as the reduction power and total phenolic content (\(p<0.05\)). However, it is worth noting that even a 7% fruit addition was sufficient to significantly improve the antioxidant activity. Further increases in fruit content generally did not lead to substantial additional improvements in these parameters. Notably, significantly higher RP and TRC values were observed only at the 20% fruit addition level. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **ABTS** & **DPPH** & **RP** \\  & **[\% RSA]** & **[\% RSA]** & **RP** \\ \hline N1 & 67.36 \(\pm\) 1.89 \({}^{\text{abc}}\) & 91.30 \(\pm\) 1.08 \({}^{\text{c}}\) & 0.24 \(\pm\) 0.02 \({}^{\text{a}}\) \\ N2 & 67.85 \(\pm\) 1.08 \({}^{\text{abc}}\) & 87.82 \(\pm\) 1.36 \({}^{\text{ab}}\) & 0.35 \(\pm\) 0.01 \({}^{\text{b}}\) \\ N3 & 65.47 \(\pm\) 2.42 \({}^{\text{a}}\) & 90.31 \(\pm\) 2.27 \({}^{\text{bc}}\) & 0.63 \(\pm\) 0.04 \({}^{\text{cd}}\) \\ N4 & 65.28 \(\pm\) 4.25 \({}^{\text{a}}\) & 91.97 \(\pm\) 1.44 \({}^{\text{c}}\) & 0.67 \(\pm\) 0.02 \({}^{\text{d}}\) \\ N5 & 66.29 \(\pm\) 1.15 \({}^{\text{ab}}\) & 86.28 \(\pm\) 3.72 \({}^{\text{a}}\) & 0.37 \(\pm\) 0.02 \({}^{\text{b}}\) \\ N6 & 70.85 \(\pm\) 2.36 \({}^{\text{c}}\) & 90.94 \(\pm\) 2.01 \({}^{\text{bc}}\) & 0.65 \(\pm\) 0.05 \({}^{\text{d}}\) \\ N7 & 69.56 \(\pm\) 1.38 \({}^{\text{bc}}\) & 90.49 \(\pm\) 2.13 \({}^{\text{bc}}\) & 0.58 \(\pm\) 0.02 \({}^{\text{c}}\) \\ \hline \hline \end{tabular} a-d Values are means; means with different letters for the same column are significantly different (\(p\leq 0.05\)); N1–N7—natural yogurts from different manufacturers.  
\end{table} 
Table 3: Antioxidant activity (ABTS, DPPH, RP) of extracts from commercial natural yogurts.