## 3 Results and Discussion
### Volatile Composition of the Cabernet Sauvignon Wines
Given that lactic acid content in TA-SC was the lowest, formation of the intermediary amount of ethyl lactate may also be related to esterase activities under more acidic conditions [33]. As a result of greater yield of ethyl lactate, the LP wines displayed significantly higher concentrations of total ethyl esters than D-SC and TA-SC wines (Table 2). Nonetheless, concentration of ethyl lactate was detected well below the aroma threshold (146 mg/L [30]) in all wines, indicating that this compound was unlikely to contribute directly to enhance the aromas of LP wines. Some lesser abundant ethyl esters, e.g., ethyl butanoate, ethyl lexanoate, ethyl isobutyrate, and ethyl isovalerate, were also found to be impact odorants with concentrations surpassing their respective sensory thresholds. These fatty acid ethyl esters were described to contribute to fruity aromas [31], and were generally less in LP wines compared to the SC wines (Table 2). The only exception was observed for ethyl butanoate, which was significantly higher in PreAF-LP wines than SC wines (Table 2). Among the fatty acid ethyl esters, one noticeable effect was a 2-6-fold decrease in ethyl octanoate (pear, apricot aroma [31]) in LP wines than the D-SC wines (Table 2). A further comparison was made between the corresponding fatty acid precursors of the mentioned fatty acid ethyl esters. The LP wines were again notable due to their lower concentrations of octanoic, hexanoic, decanoic, isobutyric and isovaleric acids than those presented in SC wines (Table 2). Contrary to the current study, [PERSON] et al. [22], [PERSON] et al. [25], and [PERSON] et al. [45] reported several fatty acid ethyl esters and their medium-chain intermediates retained at a higher level in LP/SC mixed culture wines. Together, these findings were in agreement with [PERSON] et al. [46] that accumulation of fatty acids precursors boosted production of fatty acid ethyl esters. Whilst medium chain fatty acids can hardly be produced by bacteria, these are mainly biosynthesised during yeast lipid metabolism from acetyl-CoA through the fatty acid synthase complex [6]. Of particular interest were the PreAF-LP wines, constantly showing higher concentrations of fatty acids and fatty acid ethyl esters compared to S-LP wines (Table 2). These observations suggest that varied yeast-bacteria interaction patterns resulting from different inoculation regimes may modulate SC upon the release of medium-chain fatty acids available for esterification. Of the four quantified acetate esters, only isoamyl acetate with banana aroma [30] was found above its sensory perception threshold, and was presented with the highest concentration in D-SC wines followed by TA-SC, PreAF-LP and S-LP wines (Table 2). The D-SC wines were also abundant in isobutyl acetate (banana aroma [31]), hexyl acetate (fruity and floral aroma [30]), and 2-phenylethyl acetate (honey, floral and fruity aroma [31]). As a consequence, the greatest levels of total acetate esters were found in D-SC wines (Table 2). By contrast, the lowest levels of acetate esters were presented in S-LP wines, whilst those in Pre-LP and TA-SC were intermediary (Table 2). Besides ethyl and acetate esters, four other esters including methyl octanoate, isoamyl hexanoate, 3-methylbutyl octanoate and isoamyl lactate were also identified in Cabernet Sauvignon wines (Table 2). Among these esters, only isoamyl lactate (cream and nut aroma [32]) in LP wines were found exceeding the sensory threshold, and were 9 and 7 times higher in PreAF-LP and S-LP treatments than D-SC, respectively. Again, the trend in isoamyl lactate concentrations were also linked to variation in lactic acid in the tested wines. Another noticeable difference was seen for 3-methylbutyl octanoate (sweet and fruity aroma [30]), which were 2\(\sim\)6 times lower in LP wines compared to the SC wines, albeit present at concentrations below threshold (Table 2). All four batches of wines contained considerable amounts of higher alcohols, which can potentially mask fruity aromas in red wines [47].