## 3 Results and Discussion
### Odor Profiles of Grain During the Ripening of Rice
\begin{table}
\begin{tabular}{l c c c c} \hline \hline \multicolumn{1}{c}{**Compounds**} & \multicolumn{4}{c}{**Log2 FC**} & \multicolumn{1}{c}{**Odor**} \\ \cline{2-5}  & **MX22 vs. YX430** & **YISM2 vs. YX430** & **YISM2 vs. MXZ2** & \\ \hline Heterocyclic compound & & & & \\ Platynecin & \(-1.22\) & ns & 1.05 & - \\
5-Aminotetrazole & \(-1.46\) & ns & 1.23 & - \\
2-Acetyl-1-pyrroline & ns & \(-3.68\) & \(-3.39\) & Popcorn, toasted, grain \\
1,5,6-trimenyl-azcyclohexylohexam-3-one & ns & ns & \(-1.68\) & - \\
6-Methyl-6-(5-methylfuran-2-y))heptan-2-one & \(-2.33\) & ns & \(2.03\) & - \\
4-Acetyl-pyrazol & ns & ns & \(-1.20\) & - \\
1,2,4,5-Tetrazin-3-Amine & ns & ns & \(-1.23\) & - \\ Ketone & & & & \\ Tetrahydrogenaryacetone & \(-1.60\) & ns & ns & Dry, musty \\
2-keto-1,1,10-trimethyl-A8-octalin & \(-1.65\) & ns & \(1.53\) & - \\ Dihydro-beta-ionone & \(-2.73\) & ns & \(2.58\) & Earthy, woody \\ Ester- & & & & \\
8-Decalactone & \(-1.82\) & ns & \(1.41\) & Creamy, coconut, fruity \\ Alcohol & & & & \\
1-Nonanol & ns & \(-1.60\) & \(-1.01\) & Fresh, floral, rose \\
2-Octanol & 1.01 & ns & \(-1.09\) & Fresh, herbal, earthy \\ Acid & & & & \\ Undecylenic acid & \(-1.63\) & ns & ns & Sweet, woody \\ \hline Compounds & & \multicolumn{4}{c}{Log2 FC} \\ \multicolumn{1}{c}{} & MX22 vs. YX430 & YISM2 vs. YX430 & YISM2 vs. MXZ2 & Odor \\ \hline Aldehyde & & & & \\ Heptanal & & ns & \(-2.55\) & \(-2.45\) & Fresh, fatty, green, \\ Cyclohexamecarboxaldehyde & ns & \(-1.07\) & ns & \\ \hline \hline \end{tabular}
\begin{tabular}{l c c c} \hline \hline \multicolumn{1}{c}{} & Log2 FC is the logarithmic value of the multiple of the change in content (\(\mu\)g/g) in the treatment group relative to the control group. MXZ2 vs. YX430, VOCs’ content difference in grains between treatment group MXZ2 and control group YX430; YISM2 vs. YX430, VOCs’ content difference in grains between treatment group YISM2 and control group YX430; YISM2 vs. MXZ2, VOCs’ content difference in grains between treatment group YISM2 and control group MXZ2. ns: There was no significant difference between groups; “-” means no finding. \\ \end{tabular}
\end{table} 
Table 1: _Cont._less than 100. However, p-cresyl acetate and n-butyl butanoate contributed very little to the overall flavor. The content of 2-AP increased with the ripening of rice grains, consistent with the finding that a previous publication reported [4]. (Z)-3-Hexen-1-ol, a green, grass-flavored compound found in many fresh fruits and vegetables, was present in rice [40]. Benzyl alcohol was more abundant in aromatic rice than in non-aromatic rice, contributing a slightly sweet flavor [41; 42]. Based on the ratio of content at 35 days to 10 days, exceeding 2, and the rOAV results (Table S7), the compounds (Z)-6-nonenal, (Z,Z)-3,6-nonadienal, 2-thiophenemethanethio, 5-methyl-2-furanmethanethiod, 2,2,6-trimethyl-cyclohexanone, and 3-octen-2-one were the most variable, and they contributed significantly to the flavor during rice-grain maturation. A rapid increase in the content of these six metabolites indicates grain maturity, making them potential markers for identifying ripening stages in rice grains. Combining the results of the differential metabolite analysis between aromatic and non-aromatic brown rice (Tables 1 and S7) identified three metabolites with an rOAV > 1: 2-AP, heptanal, and 1-nonanol. The levels of these compounds were higher in aromatic rice (YX430 and MXZ2) compared to non-aromatic rice (YSM2), contributing solely to the aroma of aromatic brown rice. Notably, 2-AP has long been recognized as a key marker for distinguishing between aromatic and non-aromatic rice. The 2-AP content and rOAV in ripening aromatic rice grains were the highest, but they made no significant contribution to the fragrance of non-aromatic rice. Heptanal significantly contributed to the aroma of aromatic rice in all four ripening stages, but it exhibited only a weak contribution to non-aromatic brown rice. Heptanal had higher content in cooked rice [17].