## 3 Results and Discussion
### Effect on Volatile Compounds  
It is known that there are cases of wine-making in which stems are used to bestow the wine with green and vegetal aroma [6]. Therefore, grape stems can be used as a source to \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \begin{tabular}{c} **Solvent Used** \\ **before** \\ **Treatment** \\ \end{tabular} & \begin{tabular}{c} **PEF Treatment** \\ \end{tabular} & \begin{tabular}{c} **US Extraction** \\ **Reaker (AU)** \\ \end{tabular} & \
\begin{tabular}{c} **Extract from** \\ **the PEF** \\ \end{tabular} &
\begin{tabular}{c} **\% Increase in** \\ **TPC** \\ \end{tabular} \\ \hline only stems & **x** & \(\checkmark\) & 0.081 \(\pm\) 0.001 \({}^{\text{a}}\) & 0.084 \(\pm\) 0.002 \({}^{\text{a}}\) & 4 \\ \hline
50\% v/v & \(\checkmark\) & **x** & 0.053 \(\pm\) 0.001 \({}^{\text{a}}\) & 0.055 \(\pm\) 0.001 \({}^{\text{a}}\) & 4 \\ methanol:water & \(\checkmark\) & \(\checkmark\) & 0.086 \(\pm\) 0.006 \({}^{\text{a}}\) & 0.101 \(\pm\) 0.005 \({}^{\text{b}}\) & 17 \\ \hline water & \(\checkmark\) & **x** & 0.051 \(\pm\) 0.001 \({}^{\text{a}}\) & 0.053 \(\pm\) 0.001 \({}^{\text{a}}\) & 4 \\  & \(\checkmark\) & \(\checkmark\) & 0.085 \(\pm\) 0.005 \({}^{\text{a}}\) & 0.115 \(\pm\) 0.005 \({}^{\text{b}}\) & 35 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Absorption of samples, resulting from various treatments, using the Folin-Ciocalteu method. Statistically significant differences (\(p<0.05\)) are denoted with superscript letters; AU: Absorbance units. extract aroma compounds for further use in the food industry. In this context, we examined whether treating stems with PEF, prior to the US-assisted extraction of the volatile compounds, can also increase the yield of aroma compounds. Representative chromatograms of the extracts are provided in Figure 1 and the results in Table 2. In the samples extracted without PEF pretreatment, a total of six volatile compounds were identified, whose total content was 0.73 mg/Kg. Regarding the extracts obtained using PEF treatment, prior to the US-assisted extraction, a total of eight volatile compounds were identified, whose total content was 2.44 mg/Kg. The new compounds identified were 1,14-tetradecanediol and 1-methoxy-4-methyl-benzene. Therefore, PEF pretreatment increased the total volatile content of the extract by 234%. There are even more pronounced increases for some individual compounds, such as 4-dodecanol, whose content was increased by 2100%, and hexanediolic acid, bis(2-ethylhexyl) ester, whose content increased by 716%. In all cases (except for 14- and 16-heptadecenal), the content of each compound was found to be statistically significantly higher in PEF pretreated samples. Therefore, our results highlight the superiority of PEF for use as a pretreatment step. The composition of volatile components of the grape stems is an understudied area, resulting in a lack of data regarding this topic. [PERSON] et al. [29] examined the volatile components of grape stems of the Cabernet Sauvignon and Ch \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Compounds** & **Control (mg/Kg)** & **PEF (mg/Kg)** & **\% Increase** \\ \hline Phenylethyl Alcohol & 0.04 \(\pm\) 0.01 \({}^{\text{a}}\) & 0.10 \(\pm\) 0.02 \({}^{\text{b}}\) & 150 \\ Benzene, 1-methoxy-4-methyl- & ND & 0.07 \(\pm\) 0.02 \({}^{\text{b}}\) & - \\ n-Hexadecanoic acid & 0.10 \(\pm\) 0.03 \({}^{\text{a}}\) & 0.59 \(\pm\) 0.09 \({}^{\text{b}}\) & 490 \\
1,14-Tetadecenediol & ND & 0.39 \(\pm\) 0.14 \({}^{\text{a}}\) & - \\
4-Dodecanol & 0.01 \(\pm\) 0.01 \({}^{\text{a}}\) & 0.22 \(\pm\) 0.01 \({}^{\text{b}}\) & 2100 \\ Hexanedici acid, bis(2-ethylhexyl) ester & 0.06 \(\pm\) 0.01 \({}^{\text{a}}\) & 0.49 \(\pm\) 0.05 \({}^{\text{b}}\) & 716 \\
14-Heptadecenal & 0.13 \(\pm\) 0.02 \({}^{\text{a}}\) & 0.15 \(\pm\) 0.02 \({}^{\text{a}}\) & 15 \\
16-Heptadecenal & 0.39 \(\pm\) 0.09 \({}^{\text{a}}\) & 0.43 \(\pm\) 0.05 \({}^{\text{a}}\) & 10 \\ \hline \hline _Total volatile content_ & _0.73_ & _2.44_ & 234 \\ \hline \hline \end{tabular}
\end{table}