## 3 Results and Discussion
### Antioxidant Properties of Extracts Obtained from Walnut Husks
They differ in the reaction environment (FRAP method pH = 3.6 and CUPRAC method pH = 7), which may result in a different oxidative response of the antioxidants present in the sample and thus may influence the reduction reaction. The copper reaction (CUPRAC method) is more specific for antioxidants [31]. Moreover, in FRAP, lower pH levels reduce the ionization potential, which drives electron transfer, while increasing the redox potential [29]. Regardless of the isolation method used and the method of testing antioxidant properties, the highest antioxidant properties are demonstrated by methanol extracts and the weakest by chloroform extracts. It should be clarified here that when assessing antioxidant properties, the solvent has two functions. On the one hand, as a reaction medium, it determines the effective isolation of compounds, and on the other hand, it participates in the neutralization reaction of reactive species. Taking the above into account, and additionally remembering that, according to the literature, walnut shells are a rich source of polyphenic compounds [8; 9; 32], in the next stage of the research, the total content of phenolic compounds was determined in each extract. These data are presented in Table 2.  
Data presented in Table 2 reveals that the most effective isolation technique of phenolics is PLE. This technique has repeatedly demonstrated its great separation potential resulting from short exposure of the sample to high temperature [28]. Among the solvents, the most effective in terms of isolating phenolic compounds was the most polar of the solvents used, methanol. Combining the data collected in Table 2 with the relationships presented in Figures 1 and 2, it is not surprising that methanolic PLE extracts, being the most abundant in polyphenols, have the highest antioxidant properties in each of the tested methods. According to the literature, the assessment of the antioxidant properties of compounds is influenced not only by their chemical structure, identified with the ability to donate hydrogen with electrons, chelation of metals and delocalization of an unpaired electron in the aromatic structure, but also the type of solvent in which the antioxidant properties are determined. Methods for measuring the antioxidant properties of substances are based on two main reaction mechanisms: the single electron transfer (SET) mechanism and the hydrogen transfer (HAT) mechanism [25; 31]. Both mechanisms may occur simultaneously, and the dominance of one of them is determined by, among others, type of antioxidant \begin{table}
\begin{tabular}{c c c c} \hline \hline  & \multicolumn{3}{c}{**Total Phenolics Amount in [\(\mu\)g/g]**} \\
**Extractant Type** & \multicolumn{3}{c}{**in Extracts Obtained Using the Following:**} \\ \cline{2-4}  & **Soxhlet** & **Maceration** & **PLE** \\ \hline chloroform & 588.18 \(\pm\) 16.74 \({}^{\text{a}}\) & 472.34 \(\pm\) 16.74 & 605.41 \(\pm\) 18.16 \({}^{\text{a}}\) \\ acetone & 2090.54 \(\pm\) 62.71 & 1428.31 \(\pm\) 42.85 & 3660.81 \(\pm\) 109.82 \\ ethyl acetate & 1191.89 \(\pm\) 35.75 \({}^{\text{b},c}\) & 1125.68 \(\pm\) 33.77 \({}^{\text{b},d}\) & 1239.19 \(\pm\) 37.17 \({}^{\text{c},d}\) \\ methanol & 5041.89 \(\pm\) 151.26 \({}^{\text{e}}\) & 4786.49 \(\pm\) 143.59 \({}^{\text{e}}\) & 8201.35 \(\pm\) 246.04 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: The total phenolics amount, expressed in \(\mu\)g per 1 g of dry plant material, in extracts obtained by extraction in the Soxhlet apparatus, maceration and PLE using different extractants (chloroform, acetone, ethyl acetate and methanol). Various superscripts in the row indicate data for which the difference in phenolics amounts is not statistically significantly (F\({}_{\text{cal}}\) < F\({}_{\text{tab}}\), \(p\) > 0.05, see Table S1). properties, partition coefficient and type of solvent.