## 3 Results and Discussion
### Polyphenols and Antioxidant Activity  
In the present study, the total polyphenol content (TPC) and antioxidant activity of GPP and fortified bread samples were tested. GPP achieved a TPC value of 15.02 \(\pm\) 0.63 mg GAE/g DM, while the antioxidant activity, assessed by FRAP and ABTS, resulted in 248.74 \(\pm\) 9.53 \(\upmu\)M TE/g DM and 213.53 \(\pm\) 10.16 \(\upmu\)M TE/g DM, respectively.  
The TPC and both antioxidant tests increased significantly in fortified bread GP5 and GP10 compared with the control bread GP0, with high correlation coefficients between them (r = 0.999 CPT vs. FRAP and r = 0.979 CPT vs. ABTS) (Table 7). The TPC increased 3.5-fold and 7-fold as GPP replacement increased from 0% to 5% and from 0% to 10%, respectively. Slightly lower increases were observed by [PERSON] et al. [24], with 1.9-fold and 2.5-fold for the same GPP inclusion levels reported in this study. However, [PERSON] and [PERSON] [62], with a substitution of 10% wheat flour by grape seed flour, reported a 20-fold increase. These discrepancies could be explained by the grape variety and the presence/absence of grapeseed flour in the dried GP [37].  
\begin{table}
\begin{tabular}{c c c c c c c c c} \hline \multirow{2}{*}{**Sample**} & \multicolumn{3}{c}{**Crust**} & \multicolumn{3}{c}{**Crumb**} & \multirow{2}{*}{\(\Delta\)E**} \\ \cline{2-2} \cline{4-7}  & **L*** & & & & & **L*** & & **b*** \\ \hline
**GP0** & 59.92 \(\pm\) 1.07 a & 6.90 \(\pm\) 0.59 a & 27.71 \(\pm\) 1.13 a & nd & 64.78 \(\pm\) 1.03 a & 1.70 \(\pm\) 0.28 a & 28.70 \(\pm\) 1.41 a & nd \\
**GP5** & 55.47 \(\pm\) 0.39 b & 5.71 \(\pm\) 0.47 b & 13.84 \(\pm\) 0.28 b & 14.61 & 48.34 \(\pm\) 0.58 b & 4.25 \(\pm\) 0.56 b & 17.45 \(\pm\) 0.91 b & 20.08 \\
**GP10** & 52.25 \(\pm\) 0.65 c & 4.62 \(\pm\) 0.39 c & 11.28 \(\pm\) 0.16 c & 18.28 & 47.43 \(\pm\) 0.08 b & 5.89 \(\pm\) 0.06 c & 14.74 \(\pm\) 1.16 c & 22.66 \\ \hline \end{tabular} Data with different letters in each column are significantly different for \(p\) \(<\) 0.05. nd (not determined).  
\end{table}
Table 6: Color analysis of bread samples expressed as L*(lightness), a* (red/green), and b* (blue/yellow) values. \(\Delta\)E (total color difference)  
\begin{table}
\begin{tabular}{c c c c c c} \hline \multirow{2}{*}{**Sample**} & **Crude** & \multirow{2}{*}{**Crude Protein**} & **Total** & \multirow{2}{*}{**Total Dietary Fiber**} & \multirow{2}{*}{**Ash**} & \multirow{2}{*}{**Free Sugars**} \\  & **Lipid** & & & & **Starch** & & \\ \hline
**GP0** & 0.12 \(\pm\) 0.05 a & 12.4 \(\pm\) 0.05 a & 85.5 \(\pm\) 2.82 c & 2.8 \(\pm\) 1.00 a & 1.0 \(\pm\) 0.01 a & 1.6 \(\pm\) 0.02 a \\ \hline
**GP5** & 0.50 \(\pm\) 0.22 b & 12.3 \(\pm\) 0.13 a & 82.9 \(\pm\) 0.89 b & 3.9 \(\pm\) 0.74 b & 1.1 \(\pm\) 0.01 a & 1.8 \(\pm\) 0.03 a \\ \hline
**GP10** & 0.87 \(\pm\) 0.06 b & 12.1 \(\pm\) 0.03 a & 75.3 \(\pm\) 1.95 a & 6.3 \(\pm\) 1.07 c & 1.4 \(\pm\) 0.02 b & 1.9 \(\pm\) 0.03 a \\ \hline \end{tabular} Data with different letters in each column are significantly different for \(p\) \(<\) 0.05. nd (not determined).  
\end{table}
Table 5: Chemical composition (g/100 g dry matter) of experimental breads formulated with increasing levels of grape pomace powder (GPP) in the recipe.