## 2 Results and Discussion
### Multivariate Analyses of Metabolites in the Five Rice Varieties
#### 2.2.2 Variations in Metabolic VOCs between Aromatic and Non-Aromatic Rice  
The rice sample data were repetitive, and the PLS-DA model data were reliable (Figure 3). There was a significant difference between aromatic and non-aromatic rice. Three shared metabolites were significantly differentially abundant between the non-aromatic variety Huanghuazhan and all three aromatic varieties (Meixiangzhan 2, Daohuaxiang 2, and Yexiangyoulisi): _trans_-verbenyl caprate, 1,3-dimethoxybenzene and 2-hexenal (Table 3). The metabolites significantly differentially abundant between Meizhanxiang 2 and Huanghuazhan were mainly associated with propanoate metabolism and with carbohydrate digestion and absorption (Figure 4a), while the metabolites significantly differentially abundant between Daohuaxiang 2 and Huanghuazhan were mainly associated with aminobenzoate degradation, carbon metabolism, methane metabolism, and sulfur metabolism (Figure 4c). Finally, the metabolites significantly differentially abundant between Yexiangyoulisi and Huanghuazhan were mainly associated with the propanoate metabolism and aminobenzoate degradation pathways (Figure 4e). Therefore, the metabolites that were significantly differentially abundant between Huanghuazhan rice and aromatic varieties were mainly associated with aminobenzoate degradation and with carbohydrate digestion and absorption. Seven differentially abundant metabolites were significantly differentially abundant between the non-aromatic variety Yanfeng 47 and all three aromatic varieties (Meixiangzhan 2, Daohuaxiang 2, and Yexiangyoulisi): 2-isopropyl-5-methyl-9-methylenebicyclo[4.4.0]dec-1-ene, dodecamethylcyclohexasiloxane, 1-ethyl-5-methylcyclopentene, 1,2-dimethoxybenzene, 5-methyl-2-(1-methylethyl)-2-cyclohexen-1-one, 2-ethyl-2-(hydroxy-methyl)-1,3-propanediol and 5-ethyl-2-decen-4-one (Table 3). The primary pathway associated with the differentially abundant metabolites between Meizhanxiang 2 and Yanfeng 47 was the biosynthesis of secondary metabolites (Figure 4b); The primary pathway associated with the differentially abundant metabolites between Daohuaxiang 2 and Yanfeng 47 was the degradation of aro \begin{table}
\begin{tabular}{l c c c c c c} \hline \hline
**Different Metabolites** & **RT [min]** & **DAO** & **MEI** & **YE** & **HU** & **PU** \\ \hline _trans_-Verbenyl caprate & 14.35 & 808.04 & 808.21 & 2880.04 & 808.47 & 808.536 \\
1,3-Dimethoxybenzene & 24.79 & 10,925.11 & 10,925.54 & 10,925.39 & 228,638 & 10,925.27 \\ (\(E\))-2-Hexenal & 11.16 & 1,082,045 & 455,636.2 & 776,304.4 & 28,205.43 & 28,205.94 \\
2-Isopropyl-5-methyl-9- & & & & & & \\ methylenebicyclo[4.4.0]dec-1-ene & 21.42 & 222,991.9 & 53,964.66 & 75,151.33 & 37,707.41 & 38,170.74 \\ Dodecamethylcyclohexasiloxane & 15.16 & 3,377,694 & 2,973.434 & 2,735,523 & 2,927,507 & 1.2 \(\times\) 10\({}^{8}\) \\
1-Ethyl-5-methylcyclopentene & 4.59 & 561,031.6 & 717,270.5 & 107,995 & 126,177.6 & 15,334.66 \\
1,2-Dimethoxybenzene & 24.32 & 14,742.91 & 2068.13 & 9001.32 & 62,189.44 & 179,016.1 \\
5-Methyl-2-(1-methylethyl)-2-cyclohex-1-one, & & & & & & \\
2-Ethyl-2-(hydroxymethyl)-1,3-propanediol & 14.1 & 883,789.3 & 712,170 & 723,473.1 & 64,951.88 & 64,952.48 \\
5-Ethyl-2-decen-4-one & 23.49 & 193,215.2 & 213,350.9 & 129,560.4 & 33,279.31 & 15,463.01 \\ \hline \hline \end{tabular}  
* Dao stands for the variety of Daohuaxiang 2, Ye stands for the variety of Yexiangyoulisi, Mei stands for the variety of Meixiangzhan 2, Hu stands for the variety of Huanghuazhan, and Pu stands for the variety of Yanfeng 47.  
\end{table} 
Table 3: The significant different metabolites and their relative abundance between aromatic and non-aromatic rice varieties. matic compounds (Figure 4d); and the primary pathways associated with the differentially abundant metabolites between Yexiangyoulisi and Yanfeng 47 were the degradation of aromatic compounds and the biosynthesis of secondary metabolites (Figure 4f).