## 3 Discussion
### Liquid Chromatography
\begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Compound** & **Greek** & **BVM** & **“Premium”** & **TBVM** & **[PERSON] et al.** & **[PERSON] et al.** & **[PERSON] et al.** [14]** \\  & **Vinegars** & **BVM** & **BVM** & **Byrn** & **[8]** & **[16]** & **[PERSON] et al.** [14]** \\ \hline Gallic acid & 6.97 \(\pm\) 4.03 & 11.61 \(\pm\) 9.43 & 33.53 \(\pm\) 9.33 & 21.42 \(\pm\) 0.16 & 12.4 \(\pm\) 11.8 & 64.50 \(\pm\) 10.20 & 12.56 \(\pm\) 0.86 \\ Protoctatheic acid & 1.69 \(\pm\) 0.23 & 3.48 \(\pm\) 1.00 & 12.06 \(\pm\) 1.73 & 5.09 \(\pm\) 1.42 & 6.11 \(\pm\) 7.14 & 13.40 \(\pm\) 29.94 & 3.29 \(\pm\) 0.05 \\ Caffeic acid & 0.86 \(\pm\) 0.43 & 1.52 \(\pm\) 1.32 & 10.22 \(\pm\) 3.21 & 1.61 \(\pm\) 0.10 & 3.14 \(\pm\) 3.17 & 28.70 \(\pm\) 12.40 & 3.58 \(\pm\) 0.14 \\ \(p\)-Cumaric acid & 0.47 \(\pm\) 0.37 & 1.00 \(\pm\) 1.02 & 7.09 \(\pm\) 4.09 & 4.707 \(\pm\) 0.69 & 2.45 \(\pm\) 2.52 & 22.40 \(\pm\) 33.00 & 1.97 \(\pm\) 0.05 \\ Salicylic acid & 0.26 \(\pm\) 0.01 & 0.63 \(\pm\) 0.13 & 1.21 \(\pm\) 0.45 & 1.51 \(\pm\) 0.05 & 0.29 \(\pm\) 0.26 & & \\ Syringic acid & n.d. & 1.90 \(\pm\) 1.81 & 2.71 \(\pm\) 0.57 & 8.14 \(\pm\) 1.04 & 1.05 \(\pm\) 1.11 & n.d. & \\ Pyrogallol & 0.80 \(\pm\) 0.03 & 0.80 \(\pm\) 0.23 & 1.06 \(\pm\) 0.26 & 1.12 \(\pm\) 0.003 & & & \\ Ethyl gallate & 1.13 \(\pm\) 0.41 & 0.96 \(\pm\) 0.63 & 3.44 \(\pm\) 1.47 & 2.63 \(\pm\) 0.04 & & & \\ Tyrosol & 0.99 \(\pm\) 0.19 & 1.88 \(\pm\) 1.52 & 1.85 \(\pm\) 1.16 & 2.906 \(\pm\) 0.08 & 0.27 \(\pm\) 0.36 & 109.40 \(\pm\) 60.10 & \\ Protocathetic & 0.32 \(\pm\) 0.08 & 0.92 \(\pm\) 1.07 & 2.10 \(\pm\) 1.44 & 4.62 \(\pm\) 0.07 & 6.41 \(\pm\) 8.35 & 15.70 \(\pm\) 2.40 & \\ aldehyde & & & & & & & \\ \hline \end{tabular} n.d.—not detected.  
\end{table} 
Table 2: Comparison of the content (mean; standard deviation; mg/L) of the major phenolic compounds from different studies. Our results are presented for each type of balsamic vinegar separately. Greek vinegars (\(n\) = 3; sample No. 1 was not included because a lack or different content of these compounds), BVM (\(n\) = 4), “premium” BVM (\(n\) = 5), TBVM (\(n\) = 1), [8] (\(n\) = 8), [16] (\(n\) = 6), [14] (\(n\) = 1). Average values from current study are calculated for samples containing the compounds in higher levels than limits of quantification (according to Table S6). Figure 6. Comparison of the phenolic profile of samples 1–14 obtained by HPLC analysis. Blue box—Greek balsamic vinegar; red box—BVM; green box—”premium”; BVM; purple box—TBWM. There are also differences within the categories. In Greek balsamic vinegas, sample No. 1 was the only white balsamic vinegar and shows a lower total concentration of phenolic compounds compared to other samples of the same category. In the category of Balsamic vinegar of Modena, samples No. 5 and No. 8 contained more than two times higher total concentrations of phenolic compounds than samples No. 6 and No. 7. The samples from the category of \"premium\" BVM show a good agreement of total concentrations that are even higher than in TBVM. The highest total concentration of phenolic compounds was not observed in TBVM, but in \"premium\" BVM (75.6 \(\pm\) 13.4 mg/L versus 56.7 mg/L, respectively), which can be attributed to the only one sample analyzed in the TBVM category in the study. There are, however, still some substances that are presented in significantly higher concentration in TBVM, than in any other sample analyzed. These compounds are 4-hydroxybenzaldehyde, syringealdehyde, 4-hydroxy-3-methoxycinnamaldehyde, and syringe acid. Therefore, these substances can be potential candidates for markers of the quality of balsamic vinegar samples.