# Development of Korean Indigenous Low-Temperature-Tolerant Yeast for Enhancing the Flavor of _Yakju_
## 3 Results and Discussion
### Volatile Aromatic Compounds  
Regarding the volatile aromatic compounds of _yakju_, six alcohols and fourteen esters were detected by headspace GC-MS, as shown in Table 2. Compared with the results obtained from the analysis of volatile aroma components of commercial _yakju_[40], a large concentration of higher alcohols and esters was produced. This high concentration was expected due to differences in fermentation processes (dilution) and conditions (temperature, fermentation time, etc.). In the single culture, _S. cerevisiae_ (W-3 and W153) produced more total higher alcohol content (507-556 mg/L) than non-_Saccharomyces_ strains (206-397 mg/L), whereas regarding esters, non-_Saccharomyces_ strains produced two to three times higher ester content. In the case of co-culture, the characteristics of the strains used for fermentation appeared similar, and the content of total volatile aromatic compounds increased. Some components showed higher values than those of single fermentation (isoamyl alcohol, 1-propanol, 2-phenethyl alcohol, and ethyl decanoate). Higher alcohols were quantitatively the most abundant group in _yakju_ and contributed to the aroma and essential characteristics [40]. However, excessive production of higher alcohols has a negative impact on the aroma, and an appropriate concentration can have a positive impact, such as a fruity flavor [41]. Isoamyl alcohol is a major volatile compound among higher alcohols, which boosts the aroma and flavor [42]. _S. cerevisiae_ W153 produced \(\sim\)1.5 times more isoamyl alcohol than the control strain (_S. cerevisiae_ W-3). One of the primary components of wine, 2,3-Butanediol, is produced from carbohydrates during the alcohol fermentation process and has a negative impact on liquor by causing bitter taste,  
\begin{table}
\begin{tabular}{l c c c c c c c c} \hline \hline \multicolumn{1}{c}{**Volatile Compounds**} & \multicolumn{1}{c}{**W-3**} & \multicolumn{1}{c}{**W153**} & \multicolumn{1}{c}{**N373**} & \multicolumn{1}{c}{**G818**} & \multicolumn{1}{c}{**A159**} & \multicolumn{1}{c}{**W153 + N373**} & \multicolumn{1}{c}{**W153 + G818**} & \multicolumn{1}{c}{**W153 + A159**} \\ \hline \multicolumn{1}{c}{1-Propanol} & 30.40 \(\pm\) 0.33 \({}^{\text{(10.5)}}\) & 6.82 \(\pm\) 0.19 s & 10.01 \(\pm\) 0.62 \({}^{\text{\,1}}\) & 21.41 \(\pm\) 0.31 \({}^{\text{\,4}}\) & 6.78 \(\pm\) 0.45 s & 28.38 \(\pm\) 1.13 \({}^{\text{\,4}}\) & 48.46 \(\pm\) 0.86 \({}^{\text{\,\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{\text{ \text{ \text{ \textvinegar odor, and yeast odor [43; 44]. _S. cerevisiae_ W153 could reduce the production of 2,3-butanediol by one-third. Ethyl acetate levels with higher quantities of 150 mg/L are a measure of non-_Saccharomyces_-dependent spoilage in the wine industry [45]. However, a large quantity of ethyl acetate is preferred for grain-based alcoholic beverages and spirits [46; 47]. During this study, _P. kudriavzevii_ N373 produced approximately nine times more ethyl acetate (237 mg/L) than the control. MCFA ethyl esters (ethyl hexanoate, ethyl octanoate, ethyl nonanoate, and ethyl decanoate) are fatty acid ethyl esters composed of 6-12 carbon atoms and have a low threshold, which can cause a large sensory change even in a small amount [48]. Particularly, ethyl hexanoate (ethyl caproate) is an important fragrance ingredient in products such as premium sake and exhibits a pleasant, fruity apple-like flavor [49]. Two _S. cerevisiae_ strains (W-3, W153) produced the highest amount of ethyl hexanoate (0.50-0.54 mg/L) [50], and co-culture increased the production compared to that with a non-_Saccharomyces_ single culture. In the case of ethyl nonanoate, _W. anomalous_ A159 showed the highest value of 11.54. The production of 2-phenylethyl acetate by yeast cells is responsible for a fruity, flowery flavor. _H. vineae_ G818, FPA biosynthesis-resistant-positive strain, produced \(\sim\)33.76 mg/L of 2-phenethyl acetate, which was \(\sim\)11 times higher than that of the control and co-culture with _S.