## 4 Discussion
### Effect of Oat Addition on HME Color  
PP results in Table 2 are within the color range recently published by [PERSON], et al. [46], where \(L^{*}\), \(a^{*}\), and \(b^{*}\) values were 47.6, 9.3, and 21.4, respectively for PPI and 56.5, 6.8, and 32.3, respectively for PPC. The addition of OP or OA significantly impacted the color profile of the extrudates, where PP_OP samples shifted toward a darker color. This could be attributed to the higher fat content in this mixture, making it more susceptible to lipid oxidation during the extrusion process. OA addition, on the other hand, reduced the red color of the extrudates, which is commonly reported as a result of the Maillard reaction catalyzed by the high temperature in the extruder barrel.  
measure hardness or compactness. Nevertheless, a more in-depth investigation is needed to understand this relationship.  
Microstructure images in Figure 4 showed that PP has visually a denser protein structure with more fiber alignments in the L section, which is confirmed by their high coherency coefficient value (0.504) as compared to PP_OA and PP_OP which showed a more porous structure and lower coherency coefficient value, as shown in Table 3. Similar observations were reported on the increased protein alignment of pea protein isolates in the longitudinal section [11; 12].  
In this study, the degree of fiber alignment or the density of protein structure does not necessarily reflect the cutting strength of the extrudates, and no statistically significant correlation was found between the cutting force and structural parameters quantified. PP_OP had the highest cutting force, yet it showed a relatively more porous structure as compared to PP. On the other hand, PP_OA samples with even less dense structure demonstrated a low cutting force, but this might be related to the small fat droplets and air voids that were homogeneously dispersed through the protein matrix. Similarly to the suggestions raised by [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON], [PERSON] and [PERSON] [37], one may hypothesize that both bubbles and fat droplets may act as a structure weakening element that can form and propagate micro cracks in the protein matrix. Moreover, it must be outlined that PP_OP after post treatment which had a similar hardness to chicken, but little difference in longitudinal to transversal cutting force, does not necessarily indicate poor fiber development but rather poor fiber alignment (anisotropy) as evident from the report on the coefficient of coherency as shown in Table 3.  
Analysis of the obtained data suggests that the increased porous structure of PP_OA contributed to their tendency to increase in WAC compared to PP and PP_OP. The pore sizes and intersection density both demonstrated a strong positive linear correlation with WAC (R2 = 0.93 and 0.99, respectively). However, no clear correlation was found between the structural parameters and OAC and cooking yield. All these results indicate that it is difficult to relate textural (cutting force) and functional properties (WAC, OAC, cooking yield) to a single specific structural characteristic of the meat analogues.