## 3 Results and Discussion
### Optimization of the Extraction by RSM  
The individual and combined effects of these factors on the efficiency of the isolation procedure can be estimated by statistical methods such as RSM [38]. According to the results of the single-factor experiments, three major parameters, including the microwave power, extraction time and liquid/solid ratio were further optimized by CCD combined with RSM. The center points were set as 500 W (microwave power), 15 min (extraction time), and 20 mL/g (liquid/solid ratio), and the results are shown in Table 1. Regression analyses were conducted to fit the models of the experimental data form Table 1. A second-order polynomial model was used to express the yields of the polysaccharides and essential oil, and two equations with the three independent variables are as follows:  
\[ \begin{split} Y_{1}\,=&-3.25\,+\,1.22\times 10^{-2}X_{1 }\,+\,0.25X_{2}\,+\,0.33X_{3}\,+\,4.75\times 10^{-5}X_{1}X_{2}\,+\,2.75 \times 10^{-5}X_{1}X_{3}\\ &-8.50\times 10^{-5}X_{2}X_{3}-2.50\times 10^{-6}X_{1}^{2}-1.20 \times 10^{-3}X_{2}^{2}-3.50\times 10^{-4}X_{3}^{2}\end{split}  \tag{4}\]  
\[ \begin{split} Y_{2}\,=&-0.88\,+\,2.39\times 10^{-3}X_{ 1}\,+\,4.25\times 10^{-2}X_{2}\,+\,1.59\times 10^{-2}X_{3}\\ &+\,2.50\times 10^{-6}X_{1}X_{2}\,+\,2.50\times 10^{-6}X_{1}X_{3}\,+ \,5.00\times 10^{-5}X_{2}X_{3}\\ &-1.15\times 10^{-5}X_{1}^{2}-7.45\times 10^{-3}X_{2}^{2}-7.52 \times 10^{-3}X_{3}^{2}\end{split}  \tag{5}\]  
where \(Y_{1}\) and \(Y_{2}\) are the yields of the polysaccharide and essential oil (%), respectively; \(X_{1}\) is the microwave power (W); \(X_{2}\) is the extraction time (min); and \(X_{3}\) is the liquid/solid ratio (mL/g). The significance of each coefficient was determined based on the results of an \(F\) test and the corresponding \(p\)-values, as well as the results of variance analysis (ANOVA) for the quadratic model, as shown in Tables 2 and 3. A large \(F\)-value with a small \(p\)-value indicated that the corresponding term in the model was more likely to be significant. The coefficient (\(r^{2}\)) obtained from the calculated model was 0.9836 for the polysaccharides and the lack-of-fit (\(p>0.05\)) was not found to be significant. The coefficient (\(r^{2}\)) obtained from the calculated model was 0.9941 for the essential oil and the lack-of-fit (\(p>0.05\)) was not found to be significant. As shown in Table 2, the model terms with significant effects on the polysaccharide yields (\(p<0.01\)) were determined to be the linear terms of \(X_{1}\), \(X_{2}\), and \(X_{3}\), and the quadratic terms of \(X_{1}\)\({}^{2}\), \(X_{2}\)\({}^{2}\), and \(X_{3}\)\({}^{2}\), while the interaction terms (\(X_{1}X_{2}\), \(X_{1}X_{3}\), and \(X_{2}X_{3}\)) were not significant (\(p>0.05\)). As shown in Table 3, the model terms with significant effects on the yield of the essential oil (\(p<0.01\)) were determined to be the linear terms of \(X_{2}\) and \(X_{3}\), and the quadratic terms of \(X_{1}\)\({}^{2}\), \(X_{2}\)\({}^{2}\) and \(X_{3}\)\({}^{2}\), while the interaction terms (\(X_{1}X_{2}\), \(X_{1}X_{3}\), and \(X_{2}X_{3}\)) and the linear term of \(X_{1}\) were not significant (\(p>0.05\)). Three dimensional response surfaces show the effects of the mutual interactions between the independent variables. The yields of the polysaccharides and essential oil were predicted for the