## 1 Introduction
By utilizing microwave waves to rotate the water molecules and generate heat under a low-pressure condition, the obtained food products have high nutritional and sensory qualities, without severe shrinkage [34]. Microwave vacuum drying has already been applied to various products, i.e., blueberries [35], pumpkin [36], herbs [37], potato cubes [38], carrot [39], and apple [40]. The microwave vacuum drying and rehydration characteristics of rice [1], turnip seed [33], green bell pepper [41], squid shreds [42], shitake mushroom [43], bird nest [44], pumpkin [45], and button mushroom [46] were investigated. Microwave vacuum drying is an innovative technology, but it has not been fully utilized in the commercial production of rehydrated foods. One of the challenging cases of rehydrated food is stink bean (_Parkia speciosa_) or bitter bean, a perennial plant in the pea or bean family (Fabaceae) found naturally in Southeast Asia, South Asia and Africa [47]. The beans come in bright green seedpods 30-45 cm long with 15-20 beams per pod. Its name comes from its peculiar smell as it has a skunky or gaseous, methane-like aroma. Stink beans are called by local names in different regions, e.g., Yongchak in India, Peteh or Petai in Malaysia and Singapore, and Sataw or Sator in Thailand and Indonesia [17; 48; 49; 47]. They are classified into two types, namely sataw kow and sataw dahn. The former is rounder, nuttier, and less stinky. Unlike twisted sataw kow, sataw dahn's bean pods are straight, hence the name dahn or gradahn (plank) [50]. Previous studies indicate that sataw is rich in vitamin A, calcium, phosphate, sulfidic acid, polyphenic compounds, and antioxidant capacity [47; 51; 52; 53; 54; 55; 56; 57; 58]. It possesses antidiabetic and antihypertensive bioactive peptides [47; 59] and active organic compounds including flavonoids, saponins, and tannins [50; 53; 47]. Stink beans exhibit the highest concentrations of phytochemicals and biological activity and likely compete in functional food markets [47; 49]. Stink bean peels demonstrate a potential to remove azo dye [60]. Stink beans are widely consumed in various Asian cuisines as both raw and cooked foods [47]. At present, the preservations are in forms of pickled stink beans in sour brine normally eaten with chili sauce and fresh frozen stink beans with an even stronger aroma. Most recipes still prefer the fresh stink bean to fresh frozen ones. In the monsoon season, there are abundant stink beans, resulting in a price drop. By contrast, their supplies are insufficient during the off-season and thus not available for consumption throughout the year. Additionally, the major problem for fresh stink beans is that the high water content leads to deterioration, so they become rotten. To prolong their production chain on the market, dehydration is the most common way to preserve stink beans by reducing the water activity and expand product distributions with an extended shelf life. Nowadays, stink beans are developed in forms of powders [17] and freeze-dried products [18], but there is no report about the rehydration of dried stink bean. This research work firstly compares the dehydration as well as rehydration characteristics of stink beans from microwave drying with those from convective drying and freeze drying. The dehydration time is successfully reduced by lowering the pressure in the microwave drying system previously used to dry fish [24] and durian [25]. Finally, it is demonstrated that the rehydration time is shortened by soaking the dehydrated products in water of increasing temperatures.