## 3 Results and Discussion
### Volatile Aroma Compounds
#### 3.2.7. Esters

Table 7: Concentrations (ug/L, if not otherwise indicated) of acids found in Malvazija istarska white wines produced using different yeasts determined by targeted one-dimensional gas chromatography/mass spectrometry (GC/MS) \(\ddagger\) and untargeted two-dimensional gas chromatography with time-of-flight mass spectrometry (GC\(\times\)GC/TOF-MS) sorted by decreasing Fisher’s \(F\)-ratio. higher in \(LEV\) than in \(SCE\) wine as a direct consequence of the higher concentration of lactic acid observed in the former wine (Table 1). Such an outcome was in line with previous studies on \(L\). _therntolerans_ co-fermentation [8; 19]. Ethyl lactate can have an influence on wine aroma with its buttery notes when present in high concentrations. The concentrations of important esters formed through the Ehrlich pathway from their amino acid precursors, such as ethyl 2- and 3-methylbutyrate, carriers of fruity notes, were higher in \(SCE\) than in \(LEV\) wine, suggesting a difference in their metabolism between the yeasts. This was in line with the higher concentration of isoamyl alcohol in \(SCE\) wine (Table 6) and with the fact that the mentioned esters and alcohol are formed from the same amino acid precursors, leucine and isoleucine. Concentrations of major linear medium-chain ethyl esters, such as ethyl hexanoate, octanoate, and decanoate formed from acetyl-CoA within the FAS complex, did not significantly differ between the two treatments, although a tendency towards a higher concentration of ethyl hexanoate in \(SCE\) and ethyl decanoate in \(LEV\) wine was observed. [PERSON] et al. [17] reported an increase in the total amount of ethyl esters after sequential fermentation with \(L\). _therntolerans_ in comparison with \(S\). _cerevisiae_ monoculture, while [PERSON] et al. [6] reported the opposite after monoculture fermentation with this yeast compared to \(S\). _cerevisiae_. [PERSON] et al. [8] observed inferior levels of linear medium-chain ethyl ester obtained after sequential inoculations with \(L\). _therntolerans_, although particular strains produced quantities comparable to those found in \(S\). _cerevisiae_ control wine. Such discrepancies confirm that these effects are strain-specific, although different conditions among the studies probably also had an influence. Important odoriferous acetates, such as ethyl, isobutyl, butyl, and especially isoamyl acetate, were found in higher concentration in \(LEV\) wine (Table 8). Contrary to ethyl esters, it was previously found that the production of acetates is more dependent on the expression of alcohol acetyltransferase genes than on precursor concentrations [46; 49]. A minor acetate, 3-methylheptyl acetate, also showed an elevated concentration in \(LEV\) wine. [PERSON] et al. [50] reported an increase in acetate ester levels after sequential fermentation with \(L\). _therntolerans_ in comparison with \(S\). _cerevisiae_ in monoculture, as well as variable results with some strains exceeding and some being comparable to the levels obtained by \(S\). _cerevisiae_ control [8]. [PERSON] et al. [6] reported a decrease in the concentration of acetates as a consequence of \(L\). _therntolerans_ activity. Control \(SCE\) wine contained higher concentrations of particular minor acetates and 2-phenethyl acetate, an important wine odorant (Table 8). Isoamyl lactate and ethyl phenyl lactate were strongly influenced by \(LEV\) fermentation, and their concentrations were significantly increased compared to those observed in \(SCE\) control wine, thus confirming the dependence of the formation of its esters on the availability of lactic acid. The result for isoamyl lactate was in agreement with that obtained by [PERSON] et al. [25], who reported an increase in its concentration achieved by different inoculation ratios for sequentially inoculated \(L\). _therntolerans_ followed by \(S\). _cerevisiae_. For ethyl phenyl lactate, which could also be considered a marker of \(L\).