## 4 Conclusions  
This paper presents and discusses the antioxidant properties of extracts obtained from walnut husks as well as the influence of juglone on the properties. The obtained results indicate the following:  
* the examined extracts exhibit antioxidant properties, and their value depends not only on the technique used to obtain the extract, but also on the type of extracting solvent. In this context, the highest antioxidant properties demonstrate extracts obtained using PLE. In turn, methanol turned out to be the best solvent for the isolation of active compounds;
* juglone is characterized by very weak antioxidant properties;
* the antioxidant effect of the mixture containing walnut husks, methanolic extract and juglone solution is mostly additive. Antagonism is observed in the systems with high juglone content. In light of the results presented in this work, due to the rich content of phenols and strong antioxidant activity, walnut husks area good candidate for use by many industries, including the food, nutraceuticaltical, cosmetic and pharmaceutical industries. Moreover, in order to increase the ecological and economic values of the proposed waste disposal, the PLE technique, considered as a green extraction technique, should be used. The following supporting information can be downloaded at: [[https://www.mdpi.com/article/10.3390/app14072972/s1](https://www.mdpi.com/article/10.3390/app14072972/s1)]([https://www.mdpi.com/article/10.3390/app14072972/s1](https://www.mdpi.com/article/10.3390/app14072972/s1)), Figure S1: Exemplary chromatograms of juglone standard (green color) and methanolic extracts obtained in the Soxhlet apparatus before concentration (blue color) and after concentrations (red color). Table S1. Equations of Trolox calibration curves in the concentration range of 2.5-25 \(\mathrm{\SIUnitSymbolMicro g}\)/mL obtained using various methods for assessing antioxidant and solvents; Table S2. Equations of gallic acid calibration curves in the concentration range of 2.5-500 \(\mathrm{\SIUnitSymbolMicro g}\)/mL obtained using various solvents; Table S3. F values and \(p\) values obtained during variance analysis for the data concerning total phenolics amount, expressed in extraction in the Soxhlet apparatus, maceration and PLE using different extractants (chloroform, acetone, ethyl acetate and methanol). Data from Table 2 Bold values indicate systems where the results are statistically insignificant (F \(<\) Ftab, \(p\)\(>\) 0.05; Ftab = 7.71). \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Mixture** & **System** & **Figure** & **Volume** & **F-Values** & **\(p\)-Values** & **(Ie-Ic)-Values** & **Observed Effect** \\ \hline Soxhlet & 7 & & 20/80 & 32.39 & 0.0047 & negative & antagonism/additivism \\ extract/juglone & 8 & Figure 4A & 50/50 & 5.73 & 0.0748 & 0 & additivism \\ (0.06 mg/mL) & 9 & & 80/20 & 6.72 & 0.0606 & 0 & additivism \\ \hline Soxhlet & 7 & & 20/80 & 24.01 & 0.0081 & negative & antagonism \\ extract/juglone & 8 & Figure 4B & 50/50 & 1.65 & 0.2680 & 0 & additivism \\ (0.2 mg/mL) & 9 & & 80/20 & 5.47 & 0.0795 & 0 & additivism \\ \hline Macerate/juglone & 7 & & 20/80 & 84.19 & 0.0008 & negative & antagonism \\ (0.06 mg/mL) & 8 & Figure 4C & 50/50 & 7.26 & 0.0544 & 0 & additivism \\  & 9 & & 80/20 & 7.92 & 0.0481 & 0 & additivism \\ \hline Macerate/juglone & 7 & & 20/80 & 6.35 & 0.0652 & 0 & additivism \\ (0.2 mg/mL) & 8 & Figure 4D & 50/50 & 5.78 & 0.0741 & 0 & additivism \\  & 9 & & 80/20 & 6.33 & 0.0655 & 0 & additivism \\ \hline \hline \end{tabular}
\end{table} 
Table 3: Statistical significance (_F_ and \(p\) values) of the difference between the experimental inhibition percent (\(l_{c}\)) and calculated inhibition percent (\(l_{c}\)) for the binary mixtures of juglone and walnut husk methanolic extract at three different volume ratios and with the difference (\(l_{c}\)-\(l_{c}\)) and with the observed effect and (the resultant) antioxidant effect of the antioxidants in the mixture (_Fcrit = 7.71_).