## 3 Results
### Changes in Aroma Profile  
The changes in the aroma profile of the R-B mixed juice before and after fermentation with _L. plantarum_ TUST-232 are shown in Figure 5. The response values of the 10 sensors are reflected on a radar plot to show the changes in the aroma profile of the R-B mixed juice before and after fermentation (Figure 5A). The sensor response values of R1, R6, and R8 increased after fermentation, indicating that more aromatic compounds and alcohols were formed in the R-B mixed juice fermented by _L. plantarum_ TUST-232. The decrease in R2 sensor response value indicated that nitrogen oxide was reduced after fermentation. Principal component analysis (PCA) revealed that the first two principal components (PC1, 97.22%; PC2, 2.05%) accounted for 99.27% of the total variance (Figure 5B,C). In Figure 5B, the aroma profile of the R-B mixed juice before and after fermentation was seen to be clearly distributed along PC1 and PC2, indicating an obvious difference in the aroma profile before and after fermentation. Figure 5C shows the PCA results regarding the contribution of the sensors to aroma profile identification in the R-B mixed juice before and after fermentation. The R-B mixed juice had a higher methane content before fermentation, making the S6 sensor more capable of identifying the odor before fermentation. Changes of Antioxidant Activity and the Contents of Total Phenolic, Total Flavonoid, and Dietary Fibers  
Compared with the unfurmented R-B mixed juice, the fermented R-B mixed juice showed a significant improvement in total antioxidant capacity, iron ion-reducing ability, hydroxyl radical-scavenging activity, and superoxide anion-scavenging ability (Table 3). Specifically, after fermentation, the total antioxidant capacity increased by 12.30% and reached 94.743 umol Fe\({}^{2+}\) equivalents/100 mL; the absorbance of iron ion-reducing ability reached 0.315 versus the absorbance value of 0.297 for Trolox (0.04 mM); the hydroxyl radical-scavenging activity increased from 4.045% to 9.833% versus the scavenging activity of 16.667% for 0.075 mg/mL ascorbic acid; the superoxide anion-scavenging ability showed an increase of 59.80% and reached 7.629 U/100 mL. Additionally, the R-B mixed juice fermented with _L. plantarum_ TUST-232 showed a significant increase of 11.09% in total phenolic content and reached 32.918 mg/L after fermentation (Table 3), in contrast to no significant change in total flavonoid content. Figure 5: Radar plot (**A**), PCA score plot (**B**), and loading plot (**C**) of the aromatic compounds in the R–B mixed juice before and after fermentation detected by electronic nose. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Parameter** & **Before** & **After** \\ \hline Total antioxidant capacity & 84.369 \(\pm\) 1.891 & 94.743 \(\pm\) 1.698 * \\ (umol Fe\({}^{2+}\) equivalents/100 mL) & Iron ion-reducing ability (absorbance) & 0.261 \(\pm\) 0.009 & 0.315 \(\pm\) 0.156 * \\ Hydroxyl radical-scavenging activity (\%) & 4.045 \(\pm\) 0.639 & 9.833 \(\pm\) 1.165 * \\ Superoxide anion-scavenging ability (U/100 mL) & 4.774 \(\pm\) 0.177 & 7.629 \(\pm\) 0.292 * \\ Total phenolic (mg/L) & 29.633 \(\pm\) 1.075 & 32.918 \(\pm\) 1.193 * \\ Total flavonoid (mg/L) & 85.016 \(\pm\) 4.321 & 95.810 \(\pm\) 9.295 \\ Total dietary fiber (g/100 g) & 0.536 \(\pm\) 0.024 & 0.570 \(\pm\) 0.020 \\ Insoluble dietary fiber (g/100 g) & 0.472 \(\pm\) 0.019 & 0.492 \(\pm\) 0.021 \\ Soluble dietary fiber (g/100 g) & 0.059 \(\pm\) 0.043 & 0.078 \(\pm\) 0.017 \\ \hline \hline \end{tabular} The error bars indicate means \(\pm\) SD (\(n=3\)); the differences between groups were analyzed by a two-tailed paired Student’s _t_-test; *_p_ \(<\) 0.05.  
\end{table} 
Table 3: Changes in antioxidant activity and the contents of total phenolic, total flavonoid, and dietary fibers in the R–B mixed juice before and after fermentation with _L. plantarum_ TUST-232. Meanwhile, despite no significant changes in the contents of dietary fibers (Table 3), the R-B mixed juice fermented with _L.