## 3 Results
### Changes in Volatile Profiles Induced by Germination  
The volatile organic compounds (VOCs) generated by the BR and the GBR were extracted and determined via HS-SPME-GC-MS. According to the mass spectra data from the NIST 17 library and the Kovats retention index (RI), a total of 80 volatile compounds were identified, including 8 alkanes, 4 alkenes, 22 aldehydes, 9 furans, 12 ketones, 10 alcohols, 5 fatty acid methyl esters, and 10 compounds grouped as others (Table S2), and the concentrations of the identified VOCs in the BR and the GBR were expressed as 1-octanol (internal standard) equivalents. Similar compositions of the volatile profiles were also reported for the BR from other non-fragrant rice cultivars [14; 17]. Among the eight chemical classes of the detected VOCs, aldehydes were the most abundant volatiles ranging from 239.1 ug/kg to 280.1 ug/kg in the _Japonica_ BR (Figure 4A), in the same order of magnitude as the previously reported data [17; 18]. Compared with the contents of the aldehydes in the _Japonica_ BR, the remarkable reductions of up to 60.1% were observed for the _Japonica_ GBR after the germination process. Such drastic decreases in the contents of the VOCs were also observed for the other chemical classes such as alkanes, furans, ketones, and alcohols, with the exception of alkanes, which showed slightly increased levels in all the investigated _Japonica_ GBR upon germination treatment (Figure 4A). For the _Indica rice ZZ_, ZJZ, and LY, comparable reduction degrees in the amounts of alkenes (34.1-40.5%), aldehydes (44.5-64.1%), furans (37.7-58.1%), ketones (26.8-34.6%), and alcohols (38.4-45.4%) were observed in the GBR, respectively, when compared with those in the corresponding _Indica_ BR samples (Figure 4B). These results reveal that the germination process significantly decreases the VOC levels in the GBR, independent of the rice subspecies and cultivars, thus leading to the negative impact on the perception of the cooked whole-grain rice. To examine the aroma compounds whose contents were most significantly changed upon germination, an unsupervised PCA and a supervised OPLS-DA were conducted. The VIP score filtering was subsequently utilized to identify the volatile compounds contributing to the discrimination of the VOC profiles between the BR and the GBR (Figure 5). The top 15 discriminants consisted of 5 aldehydes (butanal, (_E,E_)-2,4-Decadienal, heptanal, pentanal, and hexanal), 3 alcohols (1-hexanol, 1-Octen-3-ol, and ethanol), 1 ketone (2-heptanone), 2 esters (methyl acetate and ethyl hexadecanoate), and 2-acetyl-1-pyrroline, one of the key compounds contributing to the typical aroma of rice [19]. Then, univariate statistical analyses were further conducted to compare the differences in the amounts of the selected individual VOCs between BR and GBR (Table 1). For the _Japonica_ cultivars NJ, LJ, and TH, the amount of myrcene exhibited the most pronounced reduction in GBR as compared with those in BR, ranging from 80.1% to 91.4%. Except for ethyl acetate, ethyl hexadecanoate, and ethanol showing increased levels, most of the listed differential VOCs presented remarkably lower levels in the GBR after germination (Table 1). Similarly,  
Figure 3: Simplified biosynthetic pathways of the metabolites responsible for the metabolic differentiations between the _Japonica_ (blue) and _Indica_ (green) cultivars of brown rice (upper cell) and germinated brown rice (lower cells). For each metabolite, different letters indicate statistically significant differences (\(p<0.05\)). significant decreases in the amounts of the discriminating VOCs were also observed for the _India_ GBR samples ZZ, ZJZ, and LY (Table 1). Figure 4: Stacked bar chart of the different chemical classes of the volatile organic compounds detected in brown rice (BR) and germinated brown rice (GBR) from the _Japonica_ (**A**) and _India_ (**B**) cultivars. Figure 5: (**A**) PCA score plot of the volatile profiling data of BR (open) and GBR (solid).