## 3 Results and Discussion
### Physical Properties of Extruded Beans
#### 3.1.2 Water Absorption and Water Solubility
Generally, extrusion-cooking parameters have a significant influence on pasting properties of the extruded bean [48]. The cpv values expressed as viscosity of extruded bean ranged between 47-104 mPas for red Toska bean and 31-63 mPas for white Aura bean extrudates. It was observed that increase in screw speed during processing had a negative influence reducing the cold paste viscosity of extruded bean (for a maximum 26%), regardless of cultivar. This can be connected with weakened gel formation ability due to a higher shear forces generated during the extrusion-cooking under higher screw speed. The increase in water addition during the extrusion-cooking caused an increase in cold paste viscosity for a maximum 57% for Aura bean cultivar. It may reflect the better gel formation ability of the extruded beans, but due to protein and fibre content this ability is lower than pure starch extrudates [49]. Various texture parameters, especially hardness, are often related to the acceptability of the final extruded product. Usually, less hard and more expanded extrudates are more appreciated for direct consumption. If extruded plant material is used as functional ingredient this feature is less important than viscosity or water binding capacity. The results showed the effect of various screw speed and water addition level on the cutting force (hardness) of the obtained extrudates for both bean cultivars (Figure 3c,d). The values of this parameters were within the range 12.09-61.43 N for Toska cultivar and 10.90-93.63 N for Aura cultivar. Increase in screw speed had a significant influence on extrudates hardness for both bean cultivars, but greater effect was observed for a white be  
Figure 3: Effect of various extrusion parameters on viscosity and cutting force changes of extruded bed beans (**a**,**c**) and white beans (**b**,**d**). with higher screw speeds were characterised by lower cutting force for about 71% due to a greater expansion. The higher rate of water addition resulted in higher cutting force of bean extrudates, maximum increase in hardness (348%) was observed if water addition increased for Aura bean extrudates. These results were correlated with lower expansion of the extrudates produced with a higher water addition. This effect was more significant for Aura bean. Such influence of the extrusion-cooking parameters on product hardness was commonly observed for different kinds of starch extrudates, including bean and legume extrudates [41]. The tested bean cultivars showed significant differences in the colour profile (Figure 4). Figure 4: Effect of various extrusion parameters on lightness (\(L^{*}\)) and colour components (redness \(a^{*}\) and yellowish \(b^{*}\)) of the extruded red beans (**a**,**c**,**e**) and white beans (**b**,**d**,**f**). Aura bean was the brighter with the higher \(L^{*}\) values in comparison with Toska bean. This effect a result of much darker colour of the red bean seeds cover. Toska cultivar showed also a higher redness (\(a^{*}\) value) and lower yellowness (\(b^{*}\) value) than Aura cultivar, mainly due to the seed cover colour. The extrusion-cooking conditions changed the colour of the processed beans. After the extrusion processing obtained extrudates were darker, more red and more yellow than unprocessed beans. Process parameters significantly affected lightness of both tested beans. Extrudates obtained with higher screw speeds were characterised by lower \(L^{*}\) value for about 16% in red bean extrudates. In contrast, water addition increase had a negative effect on \(L^{*}\) value, probably due to the lower expansion causing the extrudates to become darker. This effect was especially evident when tested red bean Toska. Process parameters had a significant influence on \(a^{*}\) and \(b^{*}\) components in white bean extrudates. Results revealed that extrudates obtained at higher screw speed were more red and yellow. Water addition increase caused a decrease in \(a^{*}\) and \(b^{*}\) colour components intensity.