## 3 Results and Discussion
### Physical Properties of Extruded Beans
#### 3.1.2 Water Absorption and Water Solubility  
Water absorption index (WAI) and water solubility index (WSI) are important functional properties that can affect other extrudate properties and even applicability. In general, WAI reflects the changes in processed material, such as starch gelatinization and protein denaturation, affecting its water holding and binding capacity. WSI is often used as an indicator of molecular degradation of components. It indicates the degree of starch fragmentation during the extrusion-cooking process [43, 44]. The influence of various extrusion parameters on WAI of red and white bean extrudates is presented in Figure 2a,b, respectively. During the research it was found that the extrudates made from both bean varieties were characterized by similar WAI values ranged 7.39-8.78 g g\({}^{-1}\) for red Toska bean and 7.22-8.17 g g\({}^{-1}\) for white Aura bean. The results showed that only the level of water addition had a significant negative impact (maximum decrease of 16%) on the WAI values of the red beans (Toska) extrudates (Supplementary Table S1). The changes in the extruder screw speed did not significantly affect the changes in WAI of the extruded Tosca variety. Similar WAI changes were observed by [PERSON] et al. [45] on four beans cultivars. They suggest that significant decrease in WAI when feed moisture (or water addition) increase is caused by less viscosity of the dough and reduction in energy provided to extruded mass resulting in less mechanical damage of starch and more compact internal structure. The opposite results were observed by [PERSON] et al. [43] for extruded bean cotyledons. They recorded that increase in raw material moisture content caused significant increase in WAI of the extrudates. Figure 1: Effect of various extrusion parameters on SME and expansion ratio of extruded red beans (**a**,**c**) and white beans (**b**,**d**). In case of white beans (Aura) extrusion-cooking parameters had no significant influence on water absorption of the obtained extrudates. Moreover, [PERSON] et al. [46] discovered that extrusion process parameters had no significant effect on extruded bean WAI changes. However, it was observed that the combined interactions of water addition and extruder screw speed had a significant effect on the changes in WAI for both tested beans varieties (Supplementary Table S2). A significant effect of extrusion-cooking parameters on the water solubility index values was found. WSI ranged from 10.43 to 45.43% for red Toska cultivar and from 12.43 to 39.43% for white Aura cultivar (Figure 2c,d). For both beans cultivars a significant negative effect of water addition on WSI was observed. WSI is a parameter that can indicate the degradation extend of the molecular components, in particular starch granules disintegration. A larger amount of water can act in a protective way during the extrusion-cooking of beans, limiting both fragmentation and thermal or mechanical degradation of individual components in the processed material. Similar effect of water level on WSI changes was observed by [PERSON] et al. [45] and [PERSON] et al. [41]. Studies have shown that an increase in extruder screw speed caused a significant increase in WSI of the extruded beans, regardless of its cultivar for a maximum 90% if 1.21 h\({}^{-1}\) was applied. With the higher screw speed, the greater shear forces are generated due to the friction and greater heat is generated. As a result, increased degradation and fragmentation of ingredients in the extruded beans can be noted. WAI and WSI ranged from 2.04 g g\({}^{-1}\) to 5.01 g g\({}^{-1}\) and 20.80% to 46.80%, respectively, for the whole legume flours of kidney bean, mung bean, pigeon pea, soybean and black soybean [47]. Figure 2: Effect of various extrusion parameters on WAI and WSI changes of extruded red beans (**a**,**c**) and white beans (**b**,**d**). Cold paste viscosity (cpv) of extruded materials reflects a retrogradation tendency of the starchy component present in a processed material.