## 3 Results and Discussion
### Impact of Ingredients and Processing Conditions on Selected Physical Properties
In their study, pellets with 20% fresh broccoli showed the lowest density (256 kg/m\({}^{3}\)), while the control mixtures, extruded at 100 rpm and 32% moisture, reached up to 379 kg/m\({}^{3}\). These findings partially align with the results of the present study--here, screw speed also had a positive effect on increasing density. However, unlike broccoli, the addition of blueberry led to an increase in BD, likely due to reduced expansion caused by the presence of sugars and pectin in the fruit. Durability is an important indicator of the mechanical quality of extruded products, reflecting their resistance to abrasion, breakage and damage under dynamic forces. This parameter depends on the internal structure of the extrudate, as well as on the raw material composition and processing conditions. In the present study, all tested samples showed relatively high durability level, although some subtle differences were observed depending on the technological parameters applied (Table 5). In the case of control samples, durability remained consistently high--between 97.61% and 98.10%--regardless of screw speed and moisture level, indicating a stable mechanical structure of the material processed under controlled conditions. The addition of 10% fresh blueberry caused a minor decrease in durability level, particularly at lower moisture content and screw speed, with values dropping to 96.69%. This may be attributed to a mild weakening of the extrudate structure, likely caused by the presence of fruit particles and potential disruption of starch network formation during extrusion-cooking process. The lowest durability values were observed in mixtures containing 30% blueberry, processed at both 60 and 100 rpm with 32% moisture, reaching 95.46%. Although this still represents a high level of mechanical resistance, it indicates a gradual weakening of structural integrity with increasing amounts of fruit-based components. An increase of mixture moisture to 36% in each tested group (0%, 10% and 30% blueberry) contributed to a partial compensation of structural weakening, with durability value increasing to the range of 96.69-97.61%. This improvement may result from better surface formation and reduced brittleness at the point of extrudate discharge. At the same time, higher screw speed did not show a significant impact on this parameter, suggesting that within the tested range, the mechanical conditions were not sufficiently distinct to noticeably influence the mechanical resistance of the final products. In presented study, the effect of the addition of fresh blueberries on shelf life was observed (the minimum value of shelf life was 94.36%, and the maximum value reached 97.00%), while changes in other process parameters did not significantly affect this result. Similar findings were obtained in the study by [PERSON] et al. [40], who found that the addition of fresh broccoli reduced the durability of pellets, with the lowest value (99.06%) observed for the sample with 30% broccoli. The highest durability (99.88%) was recorded for the control pellets. Similar observations have also been made by [PERSON] et al. [41], who found that the addition of pomace to extrudates reduced durability, particularly at higher screw speed. In their study, control extrudates had the highest durability coefficient (99.85%), while the addition of 10% pomace resulted in values ranging from 99.67% to 99.88, regardless of the type of ingredient. In the present study, it was also observed that the addition of fresh fruits, such as blueberries, reduced the durability of extrudates, with values ranging from 94.36% to 97.00%. In line with the observations of [PERSON] et al. higher screw speed led to a decrease in durability, and samples without additives had the highest durability coefficient, suggesting that the presence of plant-based ingredients affects the kinetic strength of extrudates. The Water Absorption Index (WAI) indicates the extent of modification of starch and other hydrophilic ingredients during the extrusion-cooking process.