## 3 Results and Discussion
### Volatile Flavor Evaluation of Black Rice
#### 3.5.1 Electronic Noses  
The aroma of rice is one of most important factors in determining quality. The electronic nose (E-nose) is a system designed to mimic human olfaction, relying on an array of sensors and appropriate pattern recognition methods [45]. This instrument is capable of detecting subtle changes in sample composition and is primarily used for rice classification and predicting the degree of difference between test samples [45]. Response values of the electronic nose towards the black rice with different milling degrees are listed in Table 4 and Figure 4c. The response values of the sensors (T30/1, T70/2, PA/2, P30/1, P40/2, and T40/2) decreased as the milling degree increased. The response value of the sensors (P10/1, P40/1, P30/2, T40/1, and TA/2) showed a trend of decreasing, increasing, and then decreasing with increased milling degree. The aroma attributes of cooked rice were reported to greatly correlate with certain volatile compounds, such as aldehydes and hete  
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Samples**} & **Smell** & **Appearance 1** & **Texture 2** & **Taste** & **Cold Rice** & **Score for All Sensory** \\  & _/20_ & _/20_ & _/30_ & _/25_ & **texture/5** & **Attributes 3/100** \\ \hline A & 16.50 \(\pm\) 1.93 ** & 17.62 \(\pm\) 1.49  & 16.64 \(\pm\) 4.04 [FOOTNOTE:4]Footnote 4: The difference between the two measures is a measure of the relative importance of the different  
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rocycles, and volatile flavor compounds varied with milling degree [41; 43]. As shown in Table 4, PA/2, P30/1, P30/2, and TA/2 are sensitive to organic compounds; P40/1, P40/2, T40/2, and T40/1 are sensitive to gases with high oxidizing power; T30/1 is sensitive to polar compounds; P10/1 is sensitive to nonpolar compounds (including hydrocarbon, ammonia, chlorine); and T70/2 is sensitive to aromatic compounds (such as toluene and xylene) [50; 51]. The difference response values of sensors indicated that varied volatile flavor compounds exist in cooked black rice with different milling degrees [39]. The PCA analysis, displayed in Figure 4d, showed that the importance of principal component 1 (PC1) and component 2 (PC2) were 79.6% and 16.5%, respectively. The cumulative importance of PC1 and PC2 was 96.1%, indicating the effectiveness of PCA in reflecting most of the original sample's odor data. The difference between whole black rice and milled black rice samples gradually increased with the increase in milling degree. The confidence ellipses of whole black rice (A) and refined black rice (E and F) did not overlap, indicating significant difference in the odor characteristics. Discriminant factor analysis (DFA) was applied to further provide precise discrimination between groups. In DFA analysis, the importance of discriminant factor 1 (DF1) and factor 2 (DF2) were 58.6% and 30.1%, respectively. A cumulative importance of DF1 and DF2 was 88.7%. DFA results (Figure 4e) showed A, E and F were grouped in lower left, upper right, lower right quadrants, respectively. The milled samples (B, C, and D) overlapped in the upper left quadrant, indicating that these samples may have similar volatile profiles in the headspace emitted. These results showed that both PCA and DFA can be effectively used to separate/discriminate odor characteristics of black rice samples, with DFA exhibiting more effective discriminating results. \begin{table}