## 3 Results and Discussion  
### Physical Properties of Extruded Beans  
#### 3.1.1 SME and Expansion Ratio  
Specific mechanical energy as well as expansion ratio of the extruded beans were significantly affected by the extrusion process parameters (Figure 1). As other research suggests [25; 35], both SME and expansion index are related to the viscosity of the molten mass. A more intensive extrusion process may cause increased changes in the processed material (e.g., starch degradation) which can lead to the creation a less viscous slurry [36]. [PERSON] et al. [37] indicated that greater protein content in processed material can also lead to increased energy consumption (SME) of the extrusion process due to changes in viscosity of the extruded material. SME during extrusion of beans varied within 0.184-0.489 kWh kg\({}^{-1}\) (662.4-1760.4 kJ kg\({}^{-1}\)) range for red bean Toska and within 0.228-0.480 kWh kg\({}^{-1}\) (820.8-1728.0 kJ kg\({}^{-1}\)) range for Aura white bean. The research has shown (Figure 1a,b) that, regardless of the bean cultivar, SME value significantly increased with the extruder screw speed increase (\(p<0.05\)) for about 60%. SME value was directly proportional to screw speed in the equation used for SME calculations, therefore, the observed data can be found as experimental confirmation. At the same time, the greater water addition to the extruded material reduced for about 30% the energy consumption of the extrusion process (\(p<0.05\)). Lower moisture content of the raw material may result in the formation of a more viscous dough inside the extruder, which results in a greater load of the engine [38]. The impact of both these parameters on SME changes during the extrusion-cooking process of the beans was similar to the effect observed by other researchers during the extrusion of legumes or other starch-protein raw materials [17; 38]. SME during the extrusion-cooking of white beans was slightly larger than that the red ones. Probably the lower starch content in red Toska contributed to this causing the formation of a more viscous material due to less intensive starch gelatinization and thus increasing the energy consumption of the process.  
The expansion ratio (ER) is one of the most important characteristics of the extruded products. Expansion occurs when the hot material is pushed through the extruder outlet die. At this point, the water contained in the material rapidly evaporates causing the expansion of the molten material and, as a result, a porous structure of the finished product is formed [35; 36; 39]. However, too high a water content in the processed material may limit the expansion. The expansion ratio of red beans Toska ranged from 2.20 to 4.48 while for white Aura beans higher ER values in range 2.94-5.25 were found (Figure 1c,d). The reason of these differences can be found in the chemical composition of both varieties of beans. Starch is a structure-forming component that determines the extent of expansion. The Aura cultivar (white) was characterised by higher content of the carbohydrates and lower content of the protein and fibre in comparison with Toska cultivar (red). These differences can lead to observed expansion results. The research showed that increase in screw speed had a positive effect on the expansion ratio of the obtained extrudates and increase of 26% ER was noted for the highest rpm used. The increase in the water addition during the extrusion process of beans had a negative effect on the ER of the obtained extrudates, reduction in ER was maximum 38% at the highest water dosing level. These changes were observed regardless of the type of beans used. About similar changes in ER values were reported by [PERSON] et al. [40] and [PERSON] et al. [41] in the case of the extrusion of bean as well as by [PERSON] et al. [42] in the case of the legume's extrusion.