## 3 Results and Discussion
### Influence of Process Variables on Physical Properties of Extruded Snacks
[30], where increasing the percentage of insect flour resulted in a decrease in the bulk density of extrudates. This was mainly due to increased fat content, which affected the material flow through the extruder cylinder. The elevated fat content acted as a plasticizer, influencing the structure of the extrudates and consequently their bulk density. The conducted studies showed that a decrease in bulk density corresponded to a reduction in the durability coefficient. The control samples exhibited high durability coefficient. For the screw speed set at 40, 60 and 80, the durability values are 99.85, 99.83 and 99.78%, respectively. The addition of 10% pomace results in extrudates from various ingredients having similar values, typically ranging from 99.67 to 99.88%, regardless of the type of ingredient. These values are higher at lower screw speed (40 and 60) and lower at 80. With an ingredient amount of 20% pomace, the extrudate values slightly decrease, reaching levels between 99.59 and 99.67%. Notably, extrudates from flaxseed exhibit the lowest values at 80 rpm. An increase in the percentage of extrudates to 30% results in a decrease in durability. At 40 rpm, the values range from 99.4 to 99.66%. As the screw speed  
Figure 5: Response plots of expansion index of snack pellets depending on selected plant pomace addition level and applied processing variables: (**a**) apple pomace; (**b**) chokeberry pomace; (**c**) pumpkin pomace; (**d**) flaxseed pomace; (**e**) nigella seed pomace. increases to 60 and 80, these values continue to decline, reaching a minimum of 99.03% for extrudates with nigella seed pomace at 80 rpm. The absence of ingredient yields the highest values of extrudates at each speed, suggesting that any amount of ingredient at any screw speed decreases extrudate values. The most stable values are observed with lower ingredient amounts (10%), whereas higher amounts of ingredient (20 and 30%) have a more pronounced impact in reducing these values. Analysis of control samples shows the highest values of durability at each rotational speed, indicating that any amount of ingredient at any screw speed decreases the durability of snack pellets. The most stable values are observed at lower ingredient levels (10%), while higher ingredient levels (20% and 30%) have a more pronounced impact in reducing these values (Figure 8). The findings presented by [PERSON] et al. [31] show a similar relationship, where the addition of chokeberry (_Aronia melanocarpa_ L.) at different levels (10% and 20%) to extruded snack pellets significantly affects their physical and nutritional properties. In this study, increased chokeberry pomace content generally increased antioxidant activity but may decrease pellet shelf life. Higher screw speeds reduced shelf life due to increased shear and mechanical stress during extrusion cooking. Optimal results were found at lower  
Figure 6: Response plots of bulk density of snack pellets depending on selected plant pomace addition level and applied processing variables: (**a**) apple pomace; (**b**) chokeberry pomace; (**c**) pumpkin pomace; (**d**) flasseed pomace; (**e**) nigella seed pomace. Figure 7: Snack pellets (intermediate product) with the highest and lowest bulk density: (**a**) nigella seed pomace; (**b**) chokeberry pomace. screw speeds with moderate chokeberry addition, balancing durability and nutritional enhancement. In the study by [PERSON] et al. [32], dehydrated fruit and vegetable powders (e.g., pumpkin, lotus stem and Indian gooseberry) were added to corn flour at 25% and 50% levels. The authors found that increasing the powder content generally reduced radial expansion and affected the textural properties of the pellets. Durability was best maintained at lower ingredient levels and optimized screw speeds, which is consistent with our research.