## 3 Results and Discussion
### Total Phenolic Content and Total Flavonoid Content  
Figure 2A shows the TPC of the water extracts of NNGB, FNGB, NGB, and FGB, which were 21.79 \(\pm\) 0.22, 13.88 \(\pm\) 0.61, 30.83 \(\pm\) 0.24, and 27.82 \(\pm\) 0.59 mg GAE/g, respectively. These results indicate a significant decline in the TPC of the water extracts after fermentation of both nongermination black soy milk and germination black soy milk (\(p\) < 0.05). In addition, the TPC of the ethanol extracts of NNGB and FNGB were 35.01 \(\pm\) 1.73 mg GAE/g and 42.66 \(\pm\) 1.65 mg GAE/g, respectively. The TPC of the ethanol extracts of black soy milk increased significantly by 21.85% after fermentation (\(p\) < 0.05; Figure 2B). The TPC of the ethanol extracts of NGB and FGB were 47.48 \(\pm\) 0.15 mg GAE/g and 45.78 \(\pm\) 0.88 mg GAE/g, respectively, with no significant inter-group differences (\(p\) > 0.05). In summary, the ethanol extracts of NGB and FGB contained the highest TPC.  
Figure 2: Total phenolic contents (**A**,**B**) and total flavonoid contents (**C**,**D**) in the water (**A**,**C**) and ethanol (**B**,**D**) extracts of nonfermented-nongermination black soy milk, fermented-nongermination black soy milk, nonfermented-germination black soy milk, and fermented-germination black soy milk. Data are presented as means \(\pm\) SD (\(n\) = 3). Values with different uppercase letters were significantly different based on [PERSON]’s multiple range test (\(p\) < 0.05). NNGB, nonfermented-nongermination black soy milk; FNGB, fermented-nongermination black soy milk; NGB, nonfermented-germination black soy milk; FGB, fermented-germination black soy milk; GAE, gallic acid equivalent; QE, quercetin equivalent.  
Further measurements were carried out on the TFC of different samples, and the results are shown in Figure 2C,D. The TFC of the water extracts of NNGB, FNGB, NGB, and FGB were 1.88 \(\pm\) 0.15 mg quercetin equivalent (QE)/g, 0.45 \(\pm\) 0.11 mg QE/g, 3.80 \(\pm\) 0.76 mg QE/g, and 1.65 \(\pm\) 0.25 mg QE/g, respectively (Figure 2C). This indicates that the TFC of the water extracts decreased significantly after fermentation with TWK10 (\(p\) < 0.05), which was similar to the previous phenolic content results. In addition, compared with the ethanol extract of NNGB (3.19 \(\pm\) 0.60 mg QE/g), the TFC of FNGB ethanol extract (5.43 \(\pm\) 0.54 mg QE/g) increased by 70.22% (\(p\) < 0.05; Figure 2D). Among the ethanol extract groups of germination black soy milk, FGB (1.79 \(\pm\) 0.08 mg QE/g) contained a higher level of total flavonoids compared with the NGB ethanol extract (1.40 \(\pm\) 0.03 mg QE/g). According to the above results, the TFC in the ethanol extracts of nongermination and germination black soy milk increased after fermentation with TWK10.  
During soy milk fermentation with _lactobacillus_, \(\beta\)-glucosidase hydrolyzes aglycone-containing isoflav, such as daidzin and genistin, into the deglycosylated isoflav and daizein and genistein [40]. In terms of solubility, daizdin, genistin, and glycitin had a higher hydrophilicity and are more easily soluble in water [41; 42], while aglycone-containing compounds such as genistein had a higher affinity for ethanol [43]. Therefore, it could be speculated that the significant decrease in the TPC and TFC in the water extracts of NNGB, FNGB, NGB, and FGB after fermentation (\(p\) < 0.05) was caused by glucoside hydrolysis into aglycone-containing compounds.