## 3 Results and Discussion
### Rheological Properties of Fractional RBPs  
The flow curves of 2.0% (\(w/v\)) aqueous solutions of the six fractional RBPs are shown in Figure 1. At the same shear rate, the shear stress of fractional RBP solution increased with increasing extraction temperature. Newtonian behavior of fractional RBP solutions (RBP30, RBP40, RBP50, and RBP60) extracted under low temperature (30-60 \({}^{\circ}\)C) was observed. Non-Newtonian or shear-thinning behavior occurred at high extraction temperatures (70-80 \({}^{\circ}\)C), which has been described as typical behavior of many polysaccharides in water dispersion [17]. The RBP70 and RBP80 power regression results fitted by the Ostwald-de Waele model (Equation (3)) (R\({}^{2}\)\(\geq\) 0.999) are presented as \(k\) values of 114 and 264.363 and \(n\) values of 0.944 and 0.853. The \(n\) value (flow behavior index) for 2.0% RBP70 and RBP80 solutions was lower than 1, which also suggests that the two fractional RBPs are pseudoplastic. The pseudoplastic nature of RBP70 and RBP80 reveals the intermolecular interactions between polymer chains. At low shear rate, molecular chains of RBP70 and RBP80 aqueous solution had random helical conformation with relatively high apparent viscosity, but the induced continuous increase in force may lead to molecular deformation, rod breakage, and consequently a decrease in apparent viscosity [18]. \begin{table}
\begin{tabular}{c c c} \hline \hline
**Sample Code** & **GM Content (\%)** & **RBP Yield (\%)** \\ \hline RBF & 60.77 \(\pm\) 0.02 & – \\ RBP30 & 93.82 \(\pm\) 0.82 1  & 47.47 \(\pm\) 0.42 \\ RBP40 & 93.29 \(\pm\) 0.43 1  & 49.31 \(\pm\) 0.95 \\ RBP50 & 92.88 \(\pm\) 0.38 1  & 50.28 \(\pm\) 0.58 2  \\ RBP60 & 93.10 \(\pm\) 0.84 1  & 51.31 \(\pm\) 0.95 2 \\ RBP70 & 94.67 \(\pm\) 1.29 1  & 53.20 \(\pm\) 0.68 2  \\ RBP80 & 94.58 \(\pm\) 0.80 1  & 54.35 \(\pm\) 0.72 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Glucomannan (GM) content and yield of RBPs. Apparent viscosity levels were affected by molecular weight [19]. Changes in apparent viscosity can be used to monitor the interaction between polysaccharide or conformational changes of components in aqueous solutions [20]. Temperature has a greater influence on the apparent viscosity of fractional RBPs. Figure 2 shows a relationship between the apparent viscosity of 2.0% aqueous solution of the six fractional RBPs at a shear rate of 10 s\({}^{-1}\) and the extraction temperature. It was clear that the apparent viscosity followed an increasing trend as temperature increased. RBP70 and RBP80 had far higher apparent viscosity than RBP30, RBP40, RBP50, and RBP60. As shown in Table 1, although the GM content of both RBP30 and RBP80 was 94%, the apparent viscosity of 2.0% (\(w/v\)) aqueous solution of RBP30 and RBP80 differed. RBP80 had the highest viscosity increment, about eight times that of RBP30. This phenomenon can be explained by the fact that high extraction temperature facilitates the diffusion of high-molecular-weight RBP out of the cells, which results in increased entanglement density of high-molecular-weight polysaccharides. The results agree well with the GPC results. It is very important to develop a good model description of the effects of extraction temperature on the apparent viscosity of fractional RBP solutions to accurately predict the performance of the temperature (T)-apparent viscosity (AV) process. The apparent viscosity of fractional RBP solutions was used at a shear rate of 10 s\({}^{-1}\). The obtained results are plotted in Figure 2. The apparent viscosity  
Figure 1: (**A**) Shear stress and (**B**) apparent viscosity of 2.0% (\(w/v\)) aqueous solutions of six fractional bletillae rhizome polysaccharides (RBPs) as a function of shear rate at 25 \({}^{\circ}\)C.  
Figure 2: Dependence of extraction temperature of apparent viscosity of RBPs at 10 s\({}^{-1}\), \(C_{RBP}\), was 2.0 wt%. of fractional RBPs extracted over 70 \({}^{\circ}\)C was greatly improved.