## 3 Results and Discussion
### GC\(\times\)GC-TOF-MS Volatile Metabolome
This, together with higher temperatures recorded, probably exhibited an influence on the dynamics of ripening and accumulation of sugars and had a consequential impact on the grape composition. As mentioned in Section 2.1, vine cultivation techniques between the two varieties mostly differed, which, among other factors, could have also contributed to the differences observed. Among the 11 identified norisoprenoids, 2 theaspirane isomers emerged as very potent differentiators according to variety, both of them having higher concentration in Teran than in Plavac mali wines (Table 3). At this point, the corresponding odor perception thresholds of these compounds in wine were unknown; therefore, the conclusions about their contribution to the aroma of Plavac mali and Teran wines could not be made. However, the possibility that they have an impact should not be a priory neglected. The other identified norisoprenoids also showed a tendency towards higher concentrations in Teran wines, although without statistical significance due to large intra-varietal variability. Due to its low odor perception threshold, \(\beta\)-damascenone is considered one of the impact odorants in wine in general [34]. The GC-MS analysis allowed a detection of a prevalent isomer, _trans_-\(\beta\)-damascenone, which is commonly reported in wine aroma studies. The utilization of GC\(\times\)GC-TOF-MS enabled the detection of the other isomer as well, that is _cis_-\(\beta\)-damascenone, found in a much lower concentration compared to _trans_-\(\beta\)-damascenone (Table 3). [PERSON] et al. [36] stated that the concentration of \(\beta\)-damascenone mostly depend on grape cultivation and winemaking conditions, whereas variety has a weaker influence, which could explain the absence of significant differences for \(\beta\)-damascenone isomers in this study. Among other C\({}_{13}\)-norisoprenoids, 1,1,6-trimethyl-1,2-dihydronaphthalene (TDN) and _trans_-1-(2,3,6-trimethylphenyl)l0 uta-1,3-diene (TPB) have often been found in wine at concentrations surpassing their odor perception thresholds [51], so there is a possibility they contributed to the aroma of the investigated wines as well. The sensory relevance of vistispiranes and actinidiols is still generally unknown. A very large number of benzenoids was identified by GC\(\times\)GC-TOF-MS. The average concentrations of several compounds from this group were found to be significantly different between the two investigated monovarietal wines, with higher concentrations found in Teran than in Plavac mali wines (Table 3). The highest _F_-ratio value was obtained for ethyl salicate. In our previous study with GC\(\times\)GC-TOF-MS applied for white wine varietal differentiation, many benzenoids have also been shown to be variety specific [5]. By comparing this and the mentioned previous study, it was observed that 2,3-dihydrobenzofuran and 4-ethylbenzaldehyde were statistically significant indicators of varietal origin in both cases, which implies that their potential should be further investigated. The sensory impact of the identified benzenoids has not been, to our knowledge, a subject of scientific research up to date; therefore, no conclusions could be drawn about it. Among the identified aldehydes and ketones, significant differences were determined only for 3-ethoxy-2-butanone and 3,4-dihydroxy-3-cyclobutene-1,2-dione, two ketones only tentatively identified by comparison of their mass spectra to those from commercial mass spectral libraries. Their concentrations were higher in Teran wines (Table 3). The opposite was found for alcohols, where the concentrations of a 2,3-butanediol isomer, 4-octanol, 1-octen-3-ol, and 4-hepten-1-ol were higher in Plavac mali wines, whereas only the concentration of tentatively identified 2-(1-ethoxyethoxy)-3-methyl-1,4-butanediol was higher in Teran wines. Among these compounds, only 1-octen-3-ol has often been reported among the volatiles relevant for wine aroma with its odor reminiscent of mushrooms due to relatively low odor perception threshold of 1 \(\mu\)g/L [52].