## 3 Results and Discussion
### Total Polyphenols Content (TPC)  
The total polyphenols content extracted from the bark of the walnut (_Juglans regia_ L.) ranged from 128.3 to 192.1 mg(GAE)/100 g (DM), varying according to the experimental conditions. Polyphenols contents as a function of extraction temperature, raw material fraction size and process time are presented in Figure 2. \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{3}{*}{**Set**} & \multicolumn{2}{c}{**Response 1**} & \multicolumn{2}{c}{**Response 2**} & \multicolumn{2}{c}{**Response 3**} & \multicolumn{2}{c}{**Response 4**} \\  & \multicolumn{2}{c}{**TPC 1**} & \multicolumn{2}{c}{**Flavonoids Content**} & \multicolumn{2}{c}{**Antioxidant Activity**} & \multicolumn{2}{c}{**Antioxidant Activity**} \\  & **mg(GAE)/100 g** & **mg(QE)/100 g** & **(DPPH 2) 10\({}^{-6}\) MTE/1 g** & **(FRAP 3) 10\({}^{-6}\) MTE/1 g** \\  & **(Dry Mass)** & **(Dry Mass)** & **(Dry Mass)** & **(Dry Mass)** \\ \hline
1 & 171.541 & 77.528 & 16.888 & 20.48 \\
2 & 178.222 & 80.142 & 17.252 & 21.39 \\
3 & 128.304 & 28.042 & 11.479 & 17.86 \\
4 & 143.484 & 34.470 & 12.407 & 16.87 \\
5 & 192.141 & 88.333 & 21.298 & 29.69 \\
6 & 175.907 & 80.600 & 18.444 & 24.66 \\
7 & 158.031 & 63.568 & 17.252 & 21.39 \\
8 & 164.791 & 71.959 & 16.184 & 18.64 \\
9 & 170.720 & 79.908 & 17.499 & 26.77 \\
10 & 180.000 & 74.832 & 16.881 & 20.75 \\
11 & 174.976 & 77.351 & 17.136 & 22.10 \\
12 & 162.455 & 48.381 & 14.548 & 22.95 \\
13 & 166.858 & 79.350 & 16.298 & 19.96 \\
14 & 172.055 & 73.850 & 15.645 & 18.69 \\
15 & 153.127 & 52.602 & 13.328 & 19.91 \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Results of chemical analysis. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{3}{*}{**Set**} & \multicolumn{2}{c}{**Factor 1**} & \multicolumn{2}{c}{**Factor 2**} & \multicolumn{2}{c}{**Factor 3**} & \multicolumn{2}{c}{**Extract**} & \multicolumn{1}{c}{**Extraction Yield**} \\  & **A: Temperature** & **B: Fraction Size** & **C: Process Time** & **(Dry Mass)** & **(Dry Mass)** \\  & [\({}^{\circ}\)**C**]** & **[mm]** & **[min]** & **[g]** & **[\%]** \\ \hline
1 & 110 & 1.4 & 10 & 1.533 & 16.8 \\
2 & 140 & 1.4 & 30 & 1.947 & 21.4 \\
3 & 170 & 1.4 & 50 & 2.907 & 31.8 \\
4 & 170 & 1.9 & 30 & 1.979 & 21.7 \\
5 & 140 & 0.9 & 10 & 1.605 & 17.6 \\
6 & 140 & 1.9 & 10 & 1.791 & 19.7 \\
7 & 140 & 1.9 & 50 & 1.906 & 20.9 \\
8 & 110 & 1.9 & 30 & 2.406 & 26.4 \\
9 & 140 & 1.4 & 30 & 2.786 & 30.4 \\
10 & 140 & 0.9 & 50 & 1.574 & 17.3 \\
11 & 110 & 1.4 & 50 & 2.687 & 29.5 \\
12 & 170 & 0.9 & 30 & 1.391 & 15.3 \\
13 & 110 & 0.9 & 30 & 1.891 & 20.7 \\
14 & 140 & 1.4 & 30 & 1.523 & 16.7 \\
15 & 170 & 1.4 & 10 & 1.960 & 21.5 \\ \hline \hline \end{tabular}
\end{table} 
Table 3: The extraction yield in relation to dry mass of raw material. Multivariable analysis of variance (ANOVA) performed with the use of the analytical results of total polyphenols content shows that the total polyphenols were influenced by: process temperature, raw material fraction size and process time. As mentioned above, the influence of the temperature can be represented by a second-order equation. The content of polyphenols increases with the increasing temperature value up to 131.6 \({}^{\circ}\)C and then decreases. The impact of the raw material fraction size and process time changes is linear. Details of ANOVA analysis are presented in Table 5.  
An F-value of 12.53 indicates that the model is significant. There is only a 0.07% chance that an F-value this large could occur due to noise. _p_-values less than 0.05 indicate the significance of the model terms. Significant model terms are A, B, C, A\({}^{2}\). The lack of fit F-value of 4.25 implies the lack of fit is not significant relative to the pure error. The predicted R\({}^{2}\) (0.5864) and adjusted R\({}^{2}\) (0.7672) are in reasonable agreement. The signal-to-noise ratio is referred as Adeq Precision. A ratio of 11.3318 indicates an adequate signal. The obtained model is statistically significant and can be used to navigate the analyzed space.