## 2 Results and Discussion
### Nonvolatile Compounds in Fermented Rice Samples  
The 37 identified nonvolatile compounds with their relative peak areas are listed in Table 2. They were comprised of 17 amino acids, seven organic acids, and 13 carbohydrates. Amino acids were most abundant in KR10 and least abundant in RTCL79. In particular, the amounts of phenylalanine and branched-chain amino acids such as valine, leucine, and isoleucine were much smaller in RTCL79 than in the other samples. Valine, isoleucine, leucine, and phenylalanine can be transformed into Strecker aldehydes, leading to 2-methylpropanal, 2-methylbutanal, 3-methylbutanal, and phenylacetaldehyde, respectively [38]. These Strecker aldehydes can form the alcohols 2-methylpropan-1-ol, 2-methylbutan-l-ol, 3-methylbutan-l-ol, and phenylethanolamine [38]. Phenylacetaldehyde is also the most effective precursor for the production of benzaldehyde [39]. The present study identified the presence of 2-methylbutanal, 3-methylbutanal, 3-methylbutan-l-ol, and benzaldehyde. \begin{table}
\begin{tabular}{c c c c c c c c c c c c c c c c} \hline \hline \multirow{2}{*}{**No. **} & \multirow{2}{*}{**Compounds**} & \multirow{2}{*}{**Methods**} & \multirow{2}{*}{**Methods**} & \multicolumn{2}{c}{**Relative Park Area**1 **} & \multicolumn{2}{c}{**ID*** **} & \multicolumn{2}{c}{**ID***2 **} & \multicolumn{2}{c}{**ID***3 **} & \multicolumn{2}{c}{**ID***4 **} & \multicolumn{2}{c}{**ID***5 **} & \multicolumn{2}{c}{**ID***6 **} & \multicolumn{2}{c}{**ID***7 **} & \multicolumn{2}{c}{**ID***8 **} & \multicolumn{2}{c}{**ID***9 [FOOTNOTE:9]Footnote  
Glutamic acid, which contributes to a savory and umami taste, was not detected in RTCL79 or RTJL4. Glutamic acid can be converted into \(\gamma\)-aminobutyric acid (GABA) by glutamate decarboxylase to regulate the internal pH in an acid environment [40]. GABA, which is a nonprotein amino acid, plays an important role in the sympathetic nervous system and cardiovascular function [41]. Ornithine was found in only six samples (RTCL3, RTCL31, KR7, KR10, RTCL16, and RTJL4), which constitute two _Pediococcus sp._, two _Lac. brevis sp._, _Lac. sakei sp._, and _Lac. hilgardii sp._ Ornithine is a central component of the urea cycle that facilitates the disposal of excess nitrogen and can be produced from arginine via the arginine deaminase pathway [42]. Many heterofractative LABs have the ability to produce energy by utilizing arginine in the formation of ornithine, NH\({}_{3}\), CO\({}_{2}\), and ATP [43]. The conversion of arginine via citruline into ornithine releases ammonia, which increases the pH of the medium and improves the survival of bacteria under acid stress conditions [43]. Previous studies have found that this is not only the case in obligatorily heterofractative LAB such as _Lac. sanfranciscensis_ and some strains of _Lactobacillus buchneri_, _Lac. hilgardii, Lac. reuteri_, and _Oenococcus oeni_, but also in the facultative heterofractative _Lac. plantarum_[43]. Lactic acid derived from pyruvate by lactate dehydrogenase was the predominant organic acid in the present study. Lactic acid not only improves the organoleptic properties of fermented foods [44] but also inhibits the growth of spoilage bacteria in food products. In the present study, lactic acid was much more abundant in KR7 than in rice samples fermented by other LAB. It was considered that KR7 can produce the largest amount of lactate dehydrogenase. Citric acid, succinic acid, fumaric acid, and malic acid play important roles in the TCA cycle. The metabolism of citric acid is initiated by citrate permease or citrate lyase. Citrate permease leads to the formation of succinic acid, whereas citrate lyase results in decarboxylation to pyruvate that can be converted into \(\alpha\)-acetolactone, which in turn is enzymatically reduced to 3-hydroxybutan-2-one or nonenzymatically transformed into butane-2,3-dione [45]. However, the citrate conversion to succinic acid appears to be more common in _Lactobacillus_ strains [16; 45].