## 4 Conclusions  
This investigation has provided a detailed flavor-profile analysis of rice-grain samples from three varieties (the aromatic rice varieties YX430 and MXZ2, and the non-aromatic variety YISM2) at four critical ripening stages using HS-SPME-GC-MS, detecting a total of 417 VOCs. PCA and HCA demonstrated that VOC profiles from different stages were well separated and easily distinguishable. According to OPLS-DA and Venn analysis, 115 VOCs were identified as differential metabolites across the four ripening stages in the three cultivars. In addition, 20, 13, and 23 significantly different VOCs were identified between the MXZ2-vs.-YX430, YJSM2-vs.-YX430, and YJSM2-vs.-MXZ2 comparisons, respectively. Through an rOAV analysis, 65 VOCs were identified as key aromatic compounds contributing to the aroma of rice. Most aroma-active compounds showed an accumulation pattern during grain ripening, contributing to green, sweet, fruity, nutty, popcorn, roasted, fatty, and minty odors and thereby enhancing the aroma of rice grains. The accumulation of (Z)-6-nonnel, (Z,Z)-3,6-nonadien, 2-thiophenementhanethiol, 5-methyl-2-furanmethanethiol, 2,2,6-trimethyl-cyclohexanone, and 3-octen-2-one was indicative of rice-seed maturity. Additionally, 2-AP, heptanal, and 1-nonanol were identified as key-marker metabolites distinguishing aromatic from non-aromatic brown rice. These insights help improve the understanding of flavor dynamics in rice obtained from different ripening stages, and they provide a theoretical basis for the comprehensive improvement of aromatic rice varieties.  
The following supporting information can be downloaded at [[https://www.mdpi.com/article/10.3390/foods13233776/s1](https://www.mdpi.com/article/10.3390/foods13233776/s1)]([https://www.mdpi.com/article/10.3390/foods13233776/s1](https://www.mdpi.com/article/10.3390/foods13233776/s1)): Figure S1. Total ion diagram for mixed samples spectrum; Figure S2. The loading plot of the PCA; Table S1. 417 VOCs identified by HS-SPME-GC-MS; Table S2. 212 metabolic differentials were obtained from the metabolites of YX430 grains by limiting the conditions to VIP \(>\) 1 and \(p\) < 0.05; Table S3. 187 metabolic differentials were obtained from the metabolites of MXZ2 grains by limiting the conditions to VIP \(>\) 1 and \(p\) < 0.05; Table S4:148 metabolic differentials were obtained from the metabolites of YJSM2 grains by limiting the conditions to VIP \(>\) 1 and \(p\) < 0.05; Table S5. A total of 115 differential VOCs in the ripening of rice grains of YX430, MXZ2, and YJSM2; Table S6. A total of 39 differential VOCs in the ripening of rice grains of YX430 and MXZ2, but no difference in YJSM2; Table S7. The volatile compounds with OAV values above 1 in rice grains produced from YX430, MXZ2, and YJSM2.  
Conceptualization and visualization, L.Z.; writing--original draft, L.Z. and Z.P.; formal analysis and data curation, Z.P.; investigation J.H.; resources and visualization, S.W. and T.C.; investigation, W.L.; software, X.W. and T.C.; validation, H.W.; supervision, H.C.; data curation, writing--review and editing, Z.L. and X.H.; supervision, project administration, and funding acquisition, X.H. All authors have read and agreed to the published version of the manuscript.  
This research was funded by Guangdong Province key areas' research and development plan (2020B020209000), the Guangzhou Basic and Application Basic Project (202201010586, 202102080417), the Guangdong Province rural revitalization strategy special fund seed industry revitalization project (2022-NYP-00-001), and the Guangdong Key Laboratory of New Techniques in Rice Breeding (2023B1212060042).  
Not applicable.  
The original contributions presented in this study are included in the article/Supplementary Materials. Further inquiries can be directed to the corresponding author.  
The authors declare no conflicts of interest.