## 3 Results and Discussion  
Changes in Titatable Acidity and AAB Growth According to Fermentation Temperature, Alcohol Concentration, and Initial pH  
To evaluate the optimal conditions for the six AAB strains isolated from grain vinegars from various regions in Korea, the acid-producing ability and growth according to the fermentation period were investigated in a liquid medium containing 5% alcohol. Isolates fermented at 20, 30, and 40 \({}^{\circ}\)C for 15 days showed the highest acid-producing ability at 30 \({}^{\circ}\)C (Table 2). Acetic acid bacteria produce acetic acid by consuming ethanol while growing. Therefore, the result of not showing an increase in acidity and growth rate for 3 days after inoculation can be interpreted as an isolate undergoing an induction period in which it adapts to the environment for growth, and the titratable acidity increases from day 6 of fermentation. On day 15 of fermentation at 30 \({}^{\circ}\)C, the six isolates showed an average titratable acidity of 5.53 \(\pm\) 0.13%, and the GV-5, GV-12, GV-17, and GV-16 strains showed an especially high increase. When fermented at 20 \({}^{\circ}\)C and 40 \({}^{\circ}\)C, there was no increase in the titratable acidity; however, an insignificant increase was observed when GV-12 was fermented at 40 \({}^{\circ}\)C. In contrast, growth increased the most when fermented at 20 \({}^{\circ}\)C. When fermented at 30 \({}^{\circ}\)C, the growth on day 15 of fermentation increased approximately three times, whereas growth increased about 21 times when fermented at 20 \({}^{\circ}\)C, compared to the beginning of fermentation (day 0). AAB are known to grow by decomposing alcohol to produce acetic acid [39]; therefore, it is possible that the sample with no increase in titratable acidity fermented at 20 \({}^{\circ}\)C showed an increase in microorganisms other than AAB growth. However, since the initial medium before inoculation with AAB contained 5% ethanol and 1% acetic acid, the probability of bacterial growth contamination was considered to be low. In addition, when fermented at 40 \({}^{\circ}\)C, AAB did not grow, similar to the titratable acidity. Therefore, it was determined that the six isolates showed optimal acid production and growth at 30 \({}^{\circ}\)C. In general, industrial vinegar production is performed at 30 \({}^{\circ}\)C, and it is known that acetic acid bacteria lose their activity at temperatures above 35 \({}^{\circ}\)C [12]. Therefore, this can support the result that six isolates increase the titratable acidity at 30 \({}^{\circ}\)C.  
\begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**Temp. **} & \multirow{2}{*}{**Spains**} & \multicolumn{6}{c}{**Tractable Adibility Accessing to Permeation Period Chops**} & \multicolumn{6}{c}{**Cavein LODD**s**} & \multicolumn{6}{c}{**Cavein LODD**s**} & \multicolumn{6}{c}{**Cavein LODD**s**} \\ \cline{2-13}  & & **Spains** & **0** & **3** & **6** & **9** & **12** & **15** & **0** & **3**  
To evaluate the optimal alcohol concentration for the six isolates with high acid-producing ability, the isolates were fermented at 30 \({}^{\circ}\)C for 15 days in a liquid medium with an alcohol concentration of 5-14%; then, changes in tittatable acidity and growth were measured (Table 3). The isolates showed a high increase in tittatable acidity at 5% and 8% alcohol, and the growth increased similarly; however, they did not grow at 11% or higher alcohol concentrations. At 5 and 8% alcohol, the six isolates showed average tittatable acidities of about 5.53 \(\pm\) 0.13% and 6.30 \(\pm\) 0.79% after 15 days of fermentation, respectively, i.e., 4.35 and 4.85 times higher than those at the beginning of fermentation (day 0). In other words, the tittatable acidity of the 8% alcohol concentration was higher. On the other hand, the average fermentation efficiency of the isolates at 5% and 8% alcohol concentrations was 65.31% and 47.88%, respectively, exhibiting higher fermentation efficiency at 5% alcohol concentration (Table S1).