## 3 Results and Discussion
### Improving Growth of Probiotics  
_Lactobacillus bulgarcius_ and _Bifidobacterium adolescentis_ are two classical kinds of probiotics in human intestinal tract, so effect of GE on the growth of the two probiotics was studied. Results showed that the OD\({}_{600}\) (\(X\)) of the culture medium was linearly correlated with the strain biomass (Y), and the regression equation was  
\[\mathrm{Y}=17.24X-0.04 \tag{7}\]  
The correlation coefficient \(\mathrm{R}^{2}\) was 0.9947 for _Lactobacillus bulgarcius_. The strain biomass (\(N\), OD\({}_{600}\)) and culture time (t, h) were nonlinear fitted by Logistic Model, whose equation was  
\[\mathrm{Y}=\mathrm{A}/\{1+\exp[4\mu_{\mathrm{max}}(\lambda-t)/\mathrm{A}+2]\} \tag{8}\]  
Y was log \(N_{t}/N_{0}\), in which \(N_{t}\) was real-time strain biomass (OD\({}_{600}\)), and \(N_{0}\) was initial strain biomass (OD\({}_{600}\)). A, the relative maximum concentration of strain, was log \(N_{max}/N_{0}\), in which \begin{table}
\begin{tabular}{c c c c c c c c c c} \hline \hline \multirow{2}{*}{**pH**} & \multicolumn{4}{c}{**DH of GE Acted with \(\alpha\)-Amylase (\%)**} & \multicolumn{4}{c}{**DH of GE Acted with SGA (\%)**} \\ \cline{2-10}  & **t = 0 h** & **t = 2 h** & **t = 4 h** & **t = 6 h** & **t = 0 h** & **t = 2 h** & **t = 4 h** & **t = 6 h** \\ \hline
4 & 0 & 0 & 0 & 0 & 1 & 0 & 4.05 \(\pm\) 0.24 & 4.95 \(\pm\) 0.26 & 4.95 \(\pm\) 0.34 \\
5 & 0 & 0.12 \(\pm\) 0.02 & 0.12 \(\pm\) 0.03 & 0.12 \(\pm\) 0.01 & 2 & 0 & 2.21 \(\pm\) 0.17 & 2.72 \(\pm\) 0.07 & 2.72 \(\pm\) 0.15 \\
6 & 0 & 0.74 \(\pm\) 0.04 & 0.82 \(\pm\) 0.06 & 0.82 \(\pm\) 0.07 & 3 & 0 & 0.74 \(\pm\) 0.05 & 0.82 \(\pm\) 0.05 & 0.82 \(\pm\) 0.09 \\
7 & 0 & 2.21 \(\pm\) 0.12 & 2.72 \(\pm\) 0.12 & 2.72 \(\pm\) 0.14 & 4 & 0 & 0.31 \(\pm\) 0.02 & 0.31 \(\pm\) 0.03 & 0.31 \(\pm\) 0.04 \\
8 & 0 & 1.51 \(\pm\) 0.08 & 1.75 \(\pm\) 0.14 & 1.75 \(\pm\) 0.09 & 5 & 0 & 0 & 0 & 0 \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Hydrolysis of GE under the addition of \(\alpha\)-amylase and simulated gastric acid (SGA), respectively. was the maximum strain biomass (OD\({}_{600}\)). \(\mu_{\rm max}\) (h\({}^{-1}\)) is the specific growth rate of strain, and \(\lambda\) is the hysteresis period. Meanwhile, the equation was  
\[\rm Y=35.73X-3.47 \tag{9}\]  
R\({}^{2}\) was 0.9944 for _Bifidobacterium adolescents_. Specifically, the effects of the addition of GE with different concentrations of 0-2.0 mg/mL on the growth of _Lactobacillus bulgaricus_ and _Bifidobacterium adolescents_ are shown in Figure 2A,B. The strains biomass and growth rate of the two probiotics increased with GE concentration. When the culture time reached 22 h, the OD\({}_{600}\) with adding 1.6 mg/mL GE to _Lactobacillus bulgaricus_ was 1.370 \(\pm\) 0.017, while the OD\({}_{600}\) without adding any GE was only 1.141 \(\pm\) 0.026 (\(p\) < 0.05). Similarly, the OD\({}_{600}\) with adding 1.6 mg/mL GE to _Bifidobacterium adolescents_ was 1.718 \(\pm\) 0.028, while the OD\({}_{600}\) without the addition of GE was only 1.506 \(\pm\) 0.019 (\(p\) < 0.05). Hence, the addition of GE could effectively boost the strains biomass of _Lactobacillus bulgaricus_ and _Bifidobacterium adolescents_ at the same time. Through non-linear fitting of a logistic equation, the initial strain biomass (\(N_{0}\)), the maximum strain biomass (\(N_{max}\)), the maximum specific growth rate (\(\mu_{\rm max}\)) and the arrival time (\(t_{max}\)) under different GE concentrations were calculated and listed in Table 3. Both the \(N_{max}\) and \(\mu_{\rm max}\) of _Lactobacillus bulgaricus_ grew overall but \(t_{max}\) declined with the increase of GE concentration. As GE concentration increased from 0 mg/mL to 1.6 mg/mL, the \(N_{max}\) and \(\mu_{\rm max}\) climbed up from 1.196 \(\pm\) 0.059 (OD\({}_{600}\)) to 1.391 \(\pm\) 0.029 (OD\({}_{600}\)), and 0.098 \(\pm\) 0.005 h\({}^{-1}\) to 0.118 \(\pm\) 0.007 h\({}^{-1}\), respectively. A further increase of GE concentration made the \(N_{max}\) and \(\mu_{\rm max}\) keep steady.