## 3 Results
### Color, Titntable Acidity and pH  
Color is the first sensory attribute noticed by consumers that strongly influences their perception of product quality and safety. The content of carotenoids in corn flour imparts a yellow color to the control corn-based extruded snacks [8; 53]. BPP displays a dark purple color that naturally results from its high anthocyanin content coming from the skins and from the residual pulp of bilberries, which acts as a natural colorant in the extruded snacks. \begin{table}
\begin{tabular}{l c c c c} \hline \hline  & **BPP** & **CES 0** & **CES 2** & **CES 4** & **CES 6** \\ \hline Moisture (\%) & 10.18 \(\pm\) 0.55 & 8.28 \(\pm\) 0.14  & 8.16 \(\pm\) 0.11  & 7.93 \(\pm\) 0.09  & 7.69 \(\pm\) 0.12  \\ Protein (\%) & 8.19 \(\pm\) 0.46 & 6.05 \(\pm\) 0.12  & 6.16 \(\pm\) 0.14  & 6.27 \(\pm\) 0.08  & 6.45 \(\pm\) 0.11  \\ Fat (\%) & 8.28 \(\pm\) 0.46 & 0.15 \(\pm\) 0.01  & 0.18 \(\pm\) 0.01  & 0.20 \(\pm\) 0.02  & 0.22 \(\pm\) 0.02  \\ crude fiber (\%) & 11.34 \(\pm\) 0.34 & 0.71 \(\pm\) 0.03  & 1.35 \(\pm\) 0.05  & 1.79 \(\pm\) 0.08  & 1.94 \(\pm\) 0.06  \\ Ash (\%) & 1.03 \(\pm\) 0.25 & 0.36 \(\pm\) 0.02  & 0.42 \(\pm\) 0.02  & 0.46 \(\pm\) 0.02  & 0.50 \(\pm\) 0.03  \\ \hline \hline \end{tabular} †
[FOOTNOTE:†: footnotemark: [ENDFOOTNOTE]  
Different letters in the same row indicate significant differences between corn-based extruded snack formulations (\(p<0.05\)); BPP—bilberry pomace powder; CES 0—control corn-based extruded snacks; CES 2—corn-based extruded snacks with 2% BPP addition; CES 4—corn-based extruded snacks with 4% BPP addition; CES 6—corn-based extruded snacks with 6% BPP addition.  
\end{table} 
Table 1: Effect of BPP addition on proximate composition of corn-based extruded snacks. The extruded snacks enriched with BPP exhibited considerable differences in terms of color compared with the control snacks, depending significantly on the addition level (Table 2). Lightness progressively decreased as the level of BPP addition increased. A similar tendency was reported previously in corn-extruded snacks enriched with dried fruits [12; 17] or fruit pomace powders [14]. In agreement with previous studies, the corn-based extruded snacks without enrichment present high lightness, low redness, and intense yellow shade [17]. A progressive increase in a* values was recorded, accompanied by the gradual decline of b* values as the level of BPP addition increased as a response to the increase in the anthocyanin content originating from bilberry pomace. Similar evolutions of a* and b* values have been previously reported as a result of corn-based snacks enrichment with rosehip pomace [30], chokeberry pomace [3], chokeberry, cherry, and blackcurrant pomaces [14] or elderberry and blackberry fruits [17]. The most significant effect of BPP addition was observed on the red coordinate (a* values), where the 2% addition brought about up to three times more redness because of the dark purple color of BPP. The yellow coordinated was also notably affected by enrichment; b* values decreased by 35.65% at a 2% BPP addition level. Chroma (C*), which is a measure of colorfulness or color saturation, had an interesting evolution. Chroma progressively decreased at 2% and 4% BPP addition levels and increased thereafter at the 6% addition level. The 80.19 degrees hue angle of the control corn extruded snacks (CES 0) represents a yellow hue (pure yellow at a hue angle = 90). The increased pomace content in samples led to the decline of the hue angle (h*) to 26.16 degrees at the 6% BPP addition level, which was to be expected considering that decreasing the hue angle represents the increasing preponderance of red and blue tones (red-purple at a hue angle = 0). Nevertheless, many authors have pointed out that other chemical modifications taking place during extrusions, such as caramelization, non-enzymatic browning by Maillard reaction, polymerization, and pigment degradation, may also impact the final color of extruded snacks [54].