## 3 Results and Discussion
### Free Amino Acid Contents of Commercial Kimchi Manufactured in Korea, China, and the United States  
Amino acids are produced or converted into metabolites by microorganisms [36]. Table 5 shows the free amino acid content of kimchi manufactured in Korea, China, and the United States. Among the free amino acids, glutamic acid, alanine, and glycine contribute to umami (savory taste), while leucine, isoleucine, and arginine contribute to bitterness [32]. Glutamic acid, alanine, and glycine contents in Korean commercial kimchi were significantly higher than that in kimchi from China and the United States (\(p<0.05\)). In particular, the glutamic acid content was the highest in Korean commercial kimchi (1777 \(\pm\) 342 mg/kg), compared to the relatively low levels in kimchi from China and the United States (308 \(\pm\) 376 mg/kg and 357 \(\pm\) 176 mg/kg, respectively). In contrast, the leucine and isoleucine contents were the highest in commercial kimchi from China. The arginine content was the highest in Korean commercial kimchi. The citrline, ornithine, and 2-hydroxy isoc aproic acid (HICA) contents were the highest in Korean commercial kimchi. HICA is produced by LAB mainly during the early stage of fermentation, based on the LAB composition [37]. The difference in HICA contents indicates that the LAB composition differed among the samples from the different regions. Surprisingly, the highest levels of taurine and gamma-aminobutyric acid (GABA) were observed in the commercial kimchi from China. These differences could be attributed to the use of _joofgal_ \begin{table}
\begin{tabular}{c c c c} \hline \hline  & **Korea** & **China** & **United States** \\ \hline Lactic acid & 7215 \(\pm\) 1408 \({}^{\text{c}}\) & 15,266 \(\pm\) 1655 \({}^{\text{a}}\) & 11,820 \(\pm\) 4693 \({}^{\text{b}}\) \\ Acetic acid & 2998 \(\pm\) 677 \({}^{\text{b}}\) & 4330 \(\pm\) 793 \({}^{\text{a}}\) & 3690 \(\pm\) 649 \({}^{\text{ab}}\) \\ Citric acid & - & - & 43.1 \(\pm\) 71.9 \\ Fumaric acid & 16.33 \(\pm\) 15.76 & - & - \\ Et-OH & 2629 \(\pm\) 1449 \({}^{\text{b}}\) & 7750 \(\pm\) 4009 \({}^{\text{a}}\) & 4101 \(\pm\) 2440 \({}^{\text{b}}\) \\ \hline \hline \end{tabular} Data are expressed as the mean \(\pm\) SD. Lowercase letters indicate significant differences among groups (\(p<0.05\)).  
\end{table} 
Table 4: Organic acid contents of commercial kimchi manufactured in Korea, China, and the United States (mg/kg). \begin{table}
\begin{tabular}{c c c} \hline \hline  & **Korea** & **China** & **United States** \\ \hline Sucrose & 1031 \(\pm\) 1197 \({}^{\text{a}}\) & 216 \(\pm\) 241 \({}^{\text{b}}\) & 174 \(\pm\) 211 \({}^{\text{b}}\) \\ Glucose & 10,239 \(\pm\) 4934 \({}^{\text{NS}}\) & 5533 \(\pm\) 4108 & 5962 \(\pm\) 6321 \\ Fructose & 6733 \(\pm\) 6148 \({}^{\text{a}}\) & 2916 \(\pm\) 4333 \({}^{\text{ab}}\) & 1684 \(\pm\) 3001 \({}^{\text{b}}\) \\ Galactose & 280 \(\pm\) 88 \({}^{\text{a}}\) & 39 \(\pm\) 57 \({}^{\text{b}}\) & 71 \(\pm\) 107 \({}^{\text{b}}\) \\ Mannitol & 9329 \(\pm\) 3398 \({}^{\text{b}}\) & 13,100 \(\pm\) 2082 \({}^{\text{a}}\) & 12,158 \(\pm\) 3879 \({}^{\text{ab}}\) \\ Sorbitl & 3375 \(\pm\) 3454 \({}^{\text{a}}\) & 491 \(\pm\) 862 \({}^{\text{b}}\) & 67 \(\pm\) 25 \({}^{\text{b}}\) \\ \hline \hline \end{tabular} Data are expressed as the mean \(\pm\) SD. Lowercase letters indicate significant differences among groups (\(p<0.05\)).  
\({}^{\text{NS}}\); Not significant differences among groups.  
\end{table} 
Table 3: Free sugar contents of commercial kimchi manufactured in Korea, China, and the United States (mg/kg). (salted seafood) as a sub-ingredient. Korean commercial kimchi is relatively of high quality due to the high free amino acid content, which is closely related to umami. Volatile compound contents were measured using GC-MS. Table 6 shows 36 volatile compounds detected in kimchi manufactured in Korea, China, and the United States.