## 3 Results and Discussion
### Volatile Flavor Evaluation of Black Rice
#### 3.5.2 GC-Ms  
Twelve volatile compounds, including one aliphatic/alicyclic ketones, three aliphatic aldehydes, three aromatics, one aliphatic alcohols, and two alkanes, and two N-containing compounds were identified in cooked black rice by HS-SPME with GC-MS (Tables 5 and 6). Among them, cooked whole grain black rice (A) contained a significantly larger amount of hexanal, p-xylene, 2-pentyl-furan, and guaiacol than refined black rice (F). This indi  
Figure 4: Radar map of primary descriptive attributes (**a**) (smell, appearance, texture, taste, cold rice texture) and secondary attributes (**b**) of appearance (including color, gloss of rice, rice integrity) and texture (including adhesiveness, springiness, hardness) of black rice with different milling degrees; Radar map of response value of 17 sensors (**c**); Principal component score plot (**d**) and corresponding discriminant function score plot (**e**). cated these volatile compounds were mainly distributed in the bran and easily removed by milling. The aldehydes, products derived predominantly via lipid oxidation and decomposition, had a low odor threshold. Aliphatic aldehydes (including hexanal, nonanal, decanal) have been identified and are considered as odor-active compounds in various ratios of cooked black and white rice [39; 49; 52; 53; 54]. Hexanal and 1-octen-3-ol are reported to contribute greatly to the aroma attribute of cooked rice [39; 49]. 1-Octen-3-ol and 2-amino-5-methylbenzoic acid are identified as volatile odors of raw and processed black rice [55]. Guaiacol and p-xylene are representative volatile compounds of black rice [52]. Guaiacol is responsible for a smoky flavor, a characteristic volatile flavor of black rice with a low odor threshold (3 ppb) [56]. The present study found that the guaiacol released from black rice showed an increasing (14.54-19.39 ng/g) and then decreasing (19.39-5.51 ng/g) trend with increasing degree of milling, indicating that moderate milling favors the release of guaiacol aroma substances, while excessive milling decreases the content of guaiacol. The increased trend of guaiacol by moderate milling may due to the fact that the fragmentation occurring in this process facilitates the release of typical rice-related aroma components [57]. 2-Pentyl-furan is an oxidation product of linoleic acid and linoleic acid and contributes floral and fruit odor with a 6 ppb threshold value [27; 48; 49; 58]. The content of 2-pentyl-furan decreased with increasing milling degree (54.84-12.72 ng/g), consistent with trends in previous reports [56]. The odor activity value (OAV) refers to the ratio of the volatile concentration in the aroma system to its odor threshold. OAV is an indicator of the sensory impact of aroma compound on the overall aroma [59]. A higher OAV value suggests a greater contribution of the component to the overall aroma. Generally, aroma components with OAV \(>\) 1 are considered as modified aroma components, while aroma components with OAV \(>\) 10 are named key aroma components [60]. Hexanal, nonanal, decanal, and 1-octen-3-ol were  
\begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Volatile Compound** & **CAS No.