## 3 Results and Discussion  
### Characterization and Rehydration of Stink Beans Dehydrated by Different Methods  
The comparison of moisture contents in Table 1 highlights the advantage of freeze drying with negligible water left after 72 h. By using convective drying, the dehydration time can be substantially reduced and the moisture content is lower than 5% within 6 h. Microwave drying at 35 \({}^{\circ}\)C for 10 h leaves the moisture over 13% in the stink beans. Interestingly, an increase in the temperature from 35 to 40 \({}^{\circ}\)C in drying decreases dehydration time, and a moisture content of 12% is obtained after microwave drying for 6 h. The relatively high moisture in products by microwave drying can be explained based on the classification of water into free, multilayer, and monolayer states. The free water is weakly bound and therefore conveniently evaporated by every method. Prolonged heating removes the water in multilayer and monolayer states. Compared to other methods, microwave drying tends to leave more hydration monolayer at cell walls [27]. However, a lower temperature of microwave drying generally results in high-quality dried products, such as preserving higher phenolic compounds [65]. The specific energy consumptions of microwave and convective drying are shown in Table 1. The values over 100 MJ/kg are rather high for microwave drying but comparable to a previous report on shiitake mushroom drying [43]. In contrast to the comparison from carrot drying by [PERSON] et al. [14], the specific energy consumptions by microwave dehydration are higher than those by the convective drying of stink beans in this report. Such a difference is related to the much larger size of this convective oven. The oven is capable of dehydrating more than 1 kg of stink beans, whereas the loading for the microwave oven is only around 200 g. A combination of microwave with hot air drying was recommended to increase the dehydration efficiency [23]. The initial convective drying followed by microwave heating reduces the drying time, while the quality of dried products is maintained. Table 2 shows the external appearance of dehydrated stink beans. All products slightly change their shape and colors. The green color becomes distinctly darker in the case of stink beans from microwave drying. Corresponding to the highest moisture content, the product from microwave drying at 35 \({}^{\circ}\)C is closest to the fresh stink beans. Freeze drying results in a very brittle product with the smallest deformation. The deformation after microwave drying is a slightly more than that caused by freeze drying, but significantly lower than convective drying. These findings are consistent with the report from other fruits and vegetables [23]. \begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Drying Methods** & **Dehydration Time** & **Starting Weight** & **Specific Energy Consumption** & **Moisture Content** \\  & **(h)** & **(g)** & **(MJ/kg)** & **w.b. (\%)** \\ \hline Convective Dryingat 60 \({}^{\circ}\)C & 6 & 1185 & 75 \(\pm\) 6 & 4.23 \(\pm\) 0.21 \\ Freeze Drying at \(-\)70 \({}^{\circ}\)C & 72 & 400 & N/A & 0 \\ Microwave Dryingat 35 \({}^{\circ}\)C & 10 & 200 & 146 \(\pm\) 9 & 13.6 \(\pm\) 0.7 \\ Microwave Dryingat 40 \({}^{\circ}\)C & 6 & 200 & 102 \(\pm\) 8 & 11.6 \(\pm\) 0.6 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Drying characteristics of dehydrated stink beans from different drying processes. Surface morphologies of dehydrated stalk beans are compared by FESEM images. The freeze-dried product tends to lose texture elasticity and exhibits some small pores on the surface in Figure 2b. Freeze drying is known to preserve the structure of dried products. However, greater degradation of aromatic contents due to prolonged drying and the cost of the system must be taken into account for commercial production [66]. Microwave drying results in several large micropores scattered on the surface, as shown in Figure 2c.