## 3 Results and Discussion
### GC-MS Volatile Metabolome  
A total of 40 volatile compounds were identified by GC-MS analysis, including 9 terpenes, 8 C\({}_{13}\)-norisoprenoids, four alcohols, 4 fatty acids, 13 esters, and 2 compounds with an aromatic ring. Their concentrations are reported in Table 2. The majority of these compounds are commonly present in wine in medium to relatively high concentration; thus, the choice of one-dimensional GC-MS for their analysis was considered appropriate, since no major interferences with other, minor overlapping peaks was expected [5]. Some other compounds, present in lower concentration such as particular monoterepenes, volatile phenols, and especially C\({}_{13}\)-norisoprenoids, were included either because they were not identified by GC\(\times\)GC-TOF-MS, or because they were analyzed by both techniques for the purpose of comparison. The compounds in Table 2 were sorted by chemical class and by descending \(F\)-ratio obtained by one-way ANOVA within each class. The most abundant monoterepenes were the major monoterepnols, in descending order: ggeraniol, citronello, and linalool (Table 2). Monoterpenes contribute to wine aroma with odors reminiscent of flowers and fruits. Nuances provided by linalool and ggeraniol are  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**No. ** & **Volatile Compounds** & **tx** & **ID** & **LRI\({}_{\text{exp}}\)** & **LRI\({}_{\text{kin}}\)** & **F-Ratio** & & **Variety** \\ \hline \multicolumn{8}{c}{**(minusc)**} & \multicolumn{8}{c}{**PM**} & **TE**} \\ \hline \multicolumn{8}{c}{_Terpenes_} \\
1 & Limence & 15,39 & MS, LRI & 1191 & 1196 & 7.00 & 0.43 \(\pm\) 0.18 \({}^{\ast}\) & 0.26 \(\pm\) 0.02 \({}^{\text{\text{\text@underline{\text{\text{\text{\text{\text  
commonly compared to that of roses, whereas citronellol is a carrier of citrus odors. In the investigated wines they were present in sub-threshold concentrations, but relatively close to their odor perception thresholds of 30 \(\upmu\)g/L for geraniol [34], 18 \(\upmu\)g/L for citronellol [11; 35], and 15 \(\upmu\)g/L for linalool [34] (Table S2). It is known that the odors of monoterpends, as well as some other volatile compounds, can act synergistically even when present below their odor perception thresholds [11], so it is possible that the mentioned major monoterpends, despite having odor activity values (OAV) lower than 1, contributed to the aroma of the investigated Plavac mali and Teran wines in this way. Monoterpenes derive from grapes and are considered among the most useful indicators of wine varietal origin, however mostly in white wines [11]. Among the terpen identified in this study, a statistically significant difference was found only for limonene with higher concentration found in Plavac mali wines (Table 2). In our previous analogous study on white monovarietal wines, the one-dimensional GC-MS technique was successful in identifying a much larger number of terpen, among which many were found to discriminate the wines in question [5]. For example, monoterpends such as \(\upalpha\)-terpineol and linalool, as well as limonene and others, showed high potential for varietal differentiation, with \(F\)-values much higher than that determined in this study. C\({}_{13}\)-Norisoprenoids occur in grapes of the majority of varieties. They are formed by degradation of carotenoids, such as \(\upbeta\)-carotene, lutein and others, through a number of steps and with many intermediates. Their concentrations mostly depend on parameters during pre-fermentation grape processing, fermentation and aging, and less on variety [36; 37], but these compounds were nevertheless in some cases found useful for varietal differentiation [5]. In this study, no significant differences were found for C\({}_{13}\)-norisoprenoids analyzed by GC-MS (Table 2). Among them, \(\upbeta\)-ionone, and especially \(\upbeta\)-damascenone were found in concentrations higher than their very low odor perception thresholds determined in alcoholic solution of 0.09 \(\upmu\)g/L [38] and 0.05 \(\upmu\)g/L [34], respectively.