## 3 Discussion  
### Gas Chromatography  
[PERSON] et al. (2018) quantified nine phenolic acids by GC-MS after derivatization with BSTFA. In their work, gallic acid, protocatechuric acid, and _p_-coumaric acid were the main compounds with similar concentration levels (approx. 18 mg/L); however, the results of the quantitative analysis were not completely satisfactory due to the low recovery rates of extraction of phenolic acids. In our study, we performed GC-MS and GC-FID analysis without derivatization step; thus, we were not able to identify phenolic acids in the samples. Instead, we aimed at the overall profile of other phenolic volatile organic compounds. The presence of eugenol, 4-ethylphenol, 4-ethylguaiacol, 2,4-di-_tert_-butylphenol found in the samples corresponds to the published data ([PERSON] et al., 2016; [PERSON] et al., 2017; [PERSON] et al., 2018; [PERSON] et al., 2019; [PERSON] et al., 2019). In these articles ([PERSON] et al., 2017; [PERSON] et al., 2019; [PERSON] et al., 2019), several other phenolic compounds were identified: syringol, guaiacol, 4-methylphenol, phenol, tyrosol, and 4-acetyl-2-methylphenol, which were not identified in our samples. On the other hand, we identified some compounds that were not previously reported in the balsamic vinegar samples: methyl salicylate, isopseudocumenol, thymol, 4-vinylguaiacol, 1-hydroxy-3,4,5-trimethylbenzene, allyl cresol isomer, vanillin, _trans_-isoeugenol and 2,6-di-_tert_-butylmethylphenol. The presence of thymol at a high content level (2.41%), and other compounds found only in sample No. 3 may be related to the addition of thyme honey to the vinegar ([PERSON] et al., 2019), which the manufacturer declares (Table 1). Although the addition of thyme honey is not declared in sample No. 4, it is produced by the same manufacturer, and the results suggest that the certain amount of thyme honey can also be presented in this sample (3.05% of thymol). The addition of thymol can also be used as a flavoring agent ([PERSON] et al., 2019). A comparison of the overall aroma profile of individual samples is shown in Figure 4. \begin{table}
\begin{tabular}{c c c c} \hline \hline
**Sample** & **Trademark** & **Type** & \multicolumn{2}{c}{**Approximate Price (EUR/100 mL)**} \\ \hline
1 & Galaxy & White balsamic vinegar & 0.7 \\
2 & Galaxy & Balsamic vinegar & 0.6 \\
3 & Agia Triada & Balsamic vinegar & 2.0 \\
4 & Agia Triada & Balsamic vinegar & 1.5 \\
5 & San Fabio & BVM & 0.3 \\
6 & Italiano & BVM & 0.9 \\
7 & Italiano & BVM & 0.8 \\
8 & Deluxe & BVM & 1.4 \\
9 & [PERSON] & Silver medal BVM & 11.0 \\
10 & [PERSON] & 2 \(\times\) Gold medals BVM & 15.5 \\
11 & [PERSON] & 3 \(\times\) Gold medals BVM & 23.0 \\
12 & [PERSON] & 4 \(\times\) Gold medals BVM & 35.0 \\
13 & [PERSON] & 5 \(\times\) Gold medals BVM & 53.0 \\
14 & Acetaia Casanova & TBVM & 70.0 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Balsamic vinegar samples (1–4 Greek balsamic vinegas, 5–8 balsamic vinegas of Modena, 9–13 “premium” balsamic vinegas of Modena, 14 traditional balsamic vinegar of Modena). Figure 4: A comparison of the overall aroma profile of samples 1–14 obtained by GC-FID analysis. Blue box—Creek balsamic vinegr; red box—BVM; Green box—’premium’BVM; purple box—TBVM. Spots represent each peaks of the compounds in chromatogram; the size corresponds to peak area of volatile compounds in chromatogram. Samples No. 3 and No. 4 showed a significant \(D\)-carvone content compared to the other samples. This terpenoid is found in dill seeds, which are used to flavor, including vinegars [34]. Samples No. 1 and No. 2 contained \(\alpha\)-Cedrene, the source of which is cedar wood oil. Therefore, its presence in vinegars may be related to the maturation of vinegar in barrels made of cedar or juniper wood [35]. Although the aroma of cedar wood oils is typically used in the production of soaps, room sprays, and disinfectants, it can also be used as a flavoring agent [36].