## 3 Results and Discussion
### Physiological Characterization of Grape Pomace Powder and Breads  
The moisture content, a\({}_{\text{w}}\), and pH values of GPP were respectively 6.17 \(\pm\) 0.09 g/100 g DM, 0.33 \(\pm\) 0.01, and 3.39 \(\pm\) 0.01. Technological properties and chemical values of breads in terms of water activity, moisture content, pH, volume, and specific volume along with the firmness values are reported in Table 4. The a\({}_{\text{w}}\), moisture content, and baking-loss of GP0, GP5, and GP10 samples showed no statistical differences, in contrast with other research work on bread fortification, where the moisture content generally increased with the degree of fortification [47; 48; 49]. The pH value decreased significantly in GPP-fortified bread samples compared with the control. Evidently, GPP inclusion lowered the pH in fortified bread samples, according to other researchers [50; 37]. The leavesing capacity and volume of bread depend on several factors such as the kneading condition, leaving time, rheology of the dough, type of ingredients, temperature, and type of yeast used. Inducted acidic conditions and the consequent increase in the number of positive charges in the doughs may have altered the gluten network of the samples, leading to the unfolding of gluten proteins [51]. Such structural changes would lead to a less extensible and more tenacious dough in fortified samples, as seen in alveolar and farinographic results, and finally, to a reduction of volume and specific volume (Figure 1). Moreover, acidic conditions could promote the gluten proteins' solubilization and, thus, the instability of the gluten network [52]. Indeed, endogenous proteases from wheat flour work better at a low pH and this could intensify gluten proteolysis, especially of GMP (glutenin macropolymer) [51]. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Water Activity** & **Moisture content (\%)** & **Optimume (cm3)** & **Specific (cm3/g)** & **Firmness (N)** & **Baking-Loss (\%)** \\ \hline
**GP0** & 0.96 \(\pm\) 0.01 a & 43.47 \(\pm\) 0.42 a & 5.73 \(\pm\) 0.38 a & 2623 \(\pm\) 52 a & 5.52 \(\pm\) 0.11 a & 1.0 \(\pm\) 0.10 a & 13.87 \(\pm\) 0.00 a  \\
**GP5** & 0.97 \(\pm\) 0.00 a & 41.46 \(\pm\) 1.71 a & 4.44 \(\pm\) 0.03 b & 1691 \(\pm\) 104 b & 3.59 \(\pm\) 0.27 b & 21.8 \(\pm\) 1.44 b & 14.51 \(\pm\) 1.92 a  \\
**GP10** & 0.97 \(\pm\) 0.01 a & 40.58 \(\pm\) 3.70 a & 3.98 \(\pm\) 0.01 c & 1334 \(\pm\) 63 c & 2.82 \(\pm\) 0.13 c & 23.2 \(\pm\) 1.65 c & 14.05 \(\pm\) 0.77 a  \\ \hline \hline \end{tabular}
\end{table} 
Table 4: Water activity, moisture content, pH, volume, and specific volume along with the firmness values and baking-loss of control bread (GP0) and bread fortified with grape pomace powder (GP5 and GP10). \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Sample**} & **Gelatinization Maximum** & **Start of Gelatinization** & **Gelatinization Temperature** \\  & **(AU)** & **(\({}^{\circ}\)C)** & **(\({}^{\circ}\)C)** \\ \hline
**GP0** & 1301.67 \(\pm\) 17.56 a & 64.00 \(\pm\) 0.87 a & 92.30 \(\pm\) 0.75 a \\
**GP5** & 1831.67 \(\pm\) 42.52 b & 64.00 \(\pm\) 0.87 a & 93.30 \(\pm\) 0.52 a \\
**GP10** & 1943.33 \(\pm\) 11.55 c & 64.50 \(\pm\) 1.50 a & 93.70 \(\pm\) 0.75 a \\ \hline \hline \end{tabular} Data with different letters in each column are significantly different for \(p<\) 0.05.  
\end{table} 
Table 3: Amylograph characteristics of dough supplemented with grape pomace powder. In particular, _Saccharomyces cerevisiae_, responsible for dough leavening, is reported to have an optimal pH growth rate ranging between 4 and 6. Nevertheless, low pH conditions could provide a more stressful environment, thus reducing the yeast activity [53]. According to [PERSON] et al. [54] and [PERSON] et al. [55], the bread volume decreased with the increase of the fortification level. In addition, the substitution of wheat flour with a high-dietary-fiber ingredient such as GPP in bread formulation could have impaired the volume of the samples.