## 2 Results and Discussion
### Volatile Compounds from Indonesian Rice
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**No**} & \multirow{2}{*}{**Compounds**} & \multicolumn{2}{c}{**Retention Time (s)**} & \multirow{2}{*}{**Mass 3**} & \multirow{2}{*}{**References**} & \multirow{2}{*}{**Odour Strength 4**} & \multirow{2}{*}{**Odour Description 4**} \\ \cline{3-4}  & & **1D 1** & & **2D 2** & & & \\ \hline
105 & Lilyall & 1370 & 2.46 & 189 & [30] & Medium & Floral; muguet; watery; green; powdery; cumin \\
106 & 15,cis-calamenene & 1385 & 2.19 & 159 & [21] & & \\
107 & 2,3,6-Trimethyl-naphthalene & 1405 & 2.65 & 155 & [30] & & \\
108 & 2-Undecanone & 1515 & 2.18 & 58 & [20; 21; 22; 23] & & \\
109 & Methyl ester & 1535 & 2.14 & 74 & [21] & Medium & Oily; wine; fruity; floral \\
110 & 2,6- & 1555 & 2.42 & 197 & [21] & & \\
111 & Tetradecanoic acid & 1560 & 3.22 & 60 & [25] & Low, 10\% & \\
112 & 2-Ethylhexyl & 1610 & 2.39 & 120 & [30] & Low & Mild; orchid; sweet; balsam \\
113 & 6,10,14-Trimethyl-2-pentadecanone & 1630 & 2.16 & 58 & [22] & Low & Oily; herbal; jasmine; celery; woody \\
114 & 2-Pentadecanone & 1670 & 2.25 & 58 & [30] & Medium, 10\% & Fresh; jasmine; celery \\
115 & Methyl ester & 1690 & 2.22 & 74 & [21] & & \\  & hexadecanoic acid & & & & & \\
116 & Hexadecanoic acid & & & & & \\
117 & Hexadecanoic acid, ethyl ester & 1740 & 2.26 & 88 & [25] & Low & \\
118 & 1-Hexadecanol & 1920 & 2.26 & 97 & [24] & Low & \\
119 & Heptaçoane & 2215 & 2.45 & 71 & [22] & & \\ \hline \hline \end{tabular}  
* Reported for the first time in rice samples and the identification was confirmed by standard compounds. **Internal standard. 1 1D refers to one-dimensional gas chromatography (GC) separation (in the first column). 2 2D refers to two-dimensional gas chromatography (GC\(\times\)GC) separation (in the second column). 3 Unique mass spectra. The NIST Mass Spectral Database was used to identify volatile compounds from GC\(\times\)GC coupled with time-of-flight mass spectrometry (TOFM) analyses. 4 www.thegoodscentscompany.com. Cn Odour-active compounds for principal component analysis PCA (\(n\) = running number of selected compounds). Key-marker compounds are presented in bold letters.  
\end{table} 
Table 1: _Cont._The PCA 3D biplot accounted for 83.98% of the total variance, with principal component \(1\) (PC1), PC2, and PC3 explaining 48.07%, 24.09% and 11.82%, respectively. The six rice varieties were alienated revealing the probability of distinctive volatile compounds profiles (Figure 1). The group of non-aromatic rice varieties was plotted on the positive axis of PC3, while aromatic varieties were laid on the opposite coordinate along the PC3 axis. The scent of both aromatic and non-aromatic rice involved the combination of odour-active compounds [23; 31]. In aromatic rice, two compounds in negative PC3, 2-acetyl-1-pyrroline (C13) and 2,4-Nonadienal (C43), were considered remarkably essential. Particularly, 2-acetyl-1-pyrroline occurred in relatively lower concentration compared with other volatile compounds, but it is presented in aromatic rice varieties with different levels. Eucalypttol (C27), linalool (C37), and 1H-indole (C49) were much more dominant in non-aromatic than in aromatic cultivars (positive PC3). The relative content of linalool (C37) has been reported to be increased with drought stress [41] as a result of quality improvement for some non-aromatic cultivars. The compounds with a value near zero in PC3, such as 2-butylfuran (C10), guaiacol (C33), o-cymene (C38) and trans-2-nonenal (C39), did not produce clear distinctions between aromatic and non-aromatic rice varieties due to the similar levels of these compounds in the grains. Nonetheless, in regards to the PC2 axis, the non-aromatic rice varieties can be separated. IR64 (positive PC2) can be noticeably discriminated to the C4 varieties (negative PC2). The non-aromatic rice samples studied here were developed in a major advance in rice production, as it provided higher yield potential for their specific land assignments.