## 3 Results and Discussion
### Analysis of Volatile Compounds of Embryo Rice During Storage
#### 3.2.3 Analysis of ROAV of Embryo Rice During Storage  
As shown in Figure S2A, a clustering of 11 groups of volatile compounds can be observed. The group at 0 d was dissociated from other groups. The separation between the rice stored for 60-180 d and the embryo rice stored for 240-300 d at two temperatures was clear. The results indicated that the changes in the embryo rice during the late storage period were clear. Figure S2B shows the screening of VIP > 1 volatile compounds during the storage of embryo rice. A total of 45 volatile compounds with significant contributions were selected and combined with the PCA plot in Figure S2A to obtain the hyperbolic plot in Figure S2C. The first group at 0 d is mainly located in the lower right quadrant, such as 1-ethenyl-1h-indend, N-phenylphthalimide, and 3-ethylstyrene. The second group at 60-180 d is at both temperatures and is mainly located in the upper right quadrant, such as naphthalene, alpha-calacorene, and 2-Decyne. Two groups mainly revolve around hydrocarbons. The last group is the 240 to 300 d group, located in the upper and lower left quadrant, which may be some ketones and aldehydes, such as acetone and Z-3-phenylacrylamide.  
The aroma of a food sample cannot be simply accounted for by the content of a single compound. The proportional content of volatile odor compounds cannot directly indicate the impact of compounds on the overall odor of the sample. People's olfactory sensitivity to different compounds is very different, so it is necessary to combine the compound content with its odor threshold to evaluate the contribution of compounds to the overall odor [51]. Commonly, components that possess an ROAV equal to or higher than 1 are seen as the principal flavor compounds of the sample. By contrast, components with an ROAV falling within the range of 0.1 to 1 (not including 1) have significant impacts on adjusting the overall flavor of the sample [52]. According to VIP > 1 (Figure S2B), 45 main volatile compounds were screened. The threshold was determined by consulting the data, where the compounds for which the threshold cannot be determined were not analyzed. Table S3 reveals the ROAV values for 25 compounds. For ROAVs of aldehydes and hydrocarbons >1, the greatest contribution was made during the storage of embryo rice. Aldehydes have the largest ROAV values, possibly because aldehydes are relatively abundant during storage and the threshold is low. Thus, this will cause the ROAV to be over 100. 2-Pentylfuran, naphthalene, and styrene contribute most in the early stage. 2-Hexenal, nonanal, trans-2-nonanal, and ethanol contributed more in the later stage. The temperature of 25 \({}^{\circ}\)C had the greatest effect on most of the compounds, indicating that the higher the temperature, the more volatile the compounds are, resulting in a poor quality of the rice. A total of 25 compounds with an ROAV value mentioned above were selected for pairwise relevance analysis. As shown in Figure 4D, red and blue represent positive and negative correlations, respectively. Most volatile compounds were positively correlated, except for very few hydrocarbons. There was a significant positive correlation between aldehydes and acids. Styrene showed a significant negative correlation with other volatile compounds. Because styrene smells like balsamic flowers, the smell decreases with storage time. The change in 2-pentylfuran (fruity) was consistent with that of styrene. Indole has a fecal odor that appears in late storage and is negatively correlated with other aromatic volatile compounds. Thus, the production of one substance will affect the content of another substance in embryo rice during storage, which indicates that HS-SPME-GC-MS is a feasible and reliable method for detecting certain volatile compounds in embryo rice and determining the aroma quality of embryo rice during storage [53]. The interaction of the compounds had a certain impact on the aroma quality of embryo rice during storage.