## 3 Results  
### The Amounts of Biologically Active Compounds  
Fermentation duration and conditions (aerobic or anaerobic) produced quantitative changes in vitamin C, chlorophylls, and sugars. The highest content of vitamin C was in unfermented willowerh be leaves (control), 678.35 mg 100 g\({}^{-1}\) DW. This can be clarified by the fact that vitamin C is very sensitive to rubbing, temperature changes, and drying. Analyzing the fermented leaves, the highest quantity of vitamin C was after 24 h aerobic SPF (404.32 mg 100 g\({}^{-1}\) DW) and after 24 h anaerobic SPF (357.16 mg per 100 g\({}^{-1}\) DW). The highest amounts of dehydrorosorbic acid were determined after 24 h aerobic SPF at 200.11 mg 100 g\({}^{-1}\) DW and after 24 h and 72 h anaerobic SPF at 189.69 mg 100 g\({}^{-1}\) DW and 193.39 mg 100 g\({}^{-1}\) DW, respectively. L-ascorbic acid was mainly found in the control (unfermented leaves) at a concentration of 496.44 mg 100 g\({}^{-1}\) DW, which is significantly higher compared to leaves fermented in all experiment variants (Table 1). The changes of the content of total chlorophyll, and two pigments of chlorophyll \(a\) and chlorophyll \(b\) in leaves during the fermentation process was estimated. The biggest amount of total chlorophyll in the leaves was determined after 72 h anaerobic SPF (610.03 mg 100 g\({}^{-1}\) DW) and the lowest after 24 h aerobic SPF (379.16 mg 100 g\({}^{-1}\) DW). The highest amount of chlorophyll \(a\) was determined in the leaves after 72 h anaerobic SPF (503.50 mg 100 g\({}^{-1}\) DW) and the lowest after 24 h aerobic SPF (164.49 mg 100 g\({}^{-1}\) DW), which corresponds to the trend of total chlorophyll content. The highest content of pigment of chlorophyll \(b\) was established in the control (unfermented leaves) (254.23 mg 100 g\({}^{-1}\) DW) and the lowest after 72 h fermentation under aerobic and anaerobic conditions, respectively: 106.49 mg 100 g\({}^{-1}\) DW and 106.53 mg 100 g\({}^{-1}\) DW. This is the opposite trend to chlorophyll \(a\) and total chlorophyll contents (Table 2). The highest content of total sugars in willowerb leaves was after 72 h of anaerobic SPF (8.06 mg 100 g\({}^{-1}\) DW) and the lowest after 72 h of aerobic SPF (2.79 mg 100 g\({}^{-1}\) DW). It was established that the highest amounts of fructose (2.66 mg 100 g\({}^{-1}\) DW) and glucose (3.58 mg 100 g\({}^{-1}\) DW) were identified after 72 h of anaerobic SPF and the lowest amounts after 48 h of aerobic fermentation (0.75 mg 100 g\({}^{-1}\) DW and 0.83 mg 100 g\({}^{-1}\) DW, respectively). The highest quantities of sucrose were found in unfermented leaves (2.62 mg 100 g\({}^{-1}\) DW) and the lowest quantities after 72 h aerobic fermentation (1.21 mg 100 g\({}^{-1}\) DW) (Table 3). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Fermentation Method**} & \multirow{2}{*}{**Fermentation Duration**} & **Vitamin C** & **Dehydroascorbic Acid** & **L-ascorbic Acid** \\ \cline{3-4}  & & & **mg 100 g\({}^{-1}\) DW** & \\ \hline Control (unfermented leaves) & 678.35 \(\pm\) 11.16 a 1 & 179.91 \(\pm\) 12.96 a & 496.44 \(\pm\) 21.61 a \\ Aerobic & 24 h & 404.32 \(\pm\) 30.07 b & 200.11 \(\pm\) 39.30 a & 204.20 \(\pm\) 2.32 b \\ Aerobic & 48 h & 268.47 \(\pm\) 9.55 de & 135.67 \(\pm\) 12.37 b & 132.80 \(\pm\) 19.38 d \\ Aerobic & 72 h & 241.35 \(\pm\) 5.91 e & 135.45 \(\pm\) 1.56 b & 105.89 \(\pm\) 4.53 e \\ Anaerobic & 24 h & 357.16 \(\pm\) 19.14 c & 189.69 \(\pm\) 7.52 a & 167.47 \(\pm\) 14.54 c \\ Anaerobic & 48 h & 287.18 \(\pm\) 22.80 d & 135.31 \(\pm\) 28.14 b & 151.87 \(\pm\) 5.72 cd \\ Anaerobic & 72 h & 342.80 \(\pm\) 5.33 c & 193.39 \(\pm\) 1.60 a & 149.41 \(\pm\) 4.97 cd \\ \hline \hline \end{tabular} \(p\)-values (fermentation method \(\times\) fermentation duration) & \(<\)0.0001 & \(<\)0.0039 & \(<\)0.0003 \\ \hline \hline \end{tabular}  
* The differences between the averages in columns marked by different small letters (a, b, c, d, e) are significant at \(p<\) 0.05.  
\end{table}