## 3 Results and Discussion
### In Vitro Starch Digestion of the GPP-Fortified Breads  
The hydrolysis index (HI) can be used to calculate a predicted glycemic index (pGI) values of starch-based foods and to predict the in vivo glycemic response of a food of interest [31]. In general, WWF-based breads are characterized by high HI and pGI values [32]. As reported in Table 3, both the HI and pGI values showed a decrease (\(p<0.05\)) with the progressive inclusion of GPP in bread. In particular, the HI and the corresponding pGI decreased from 100 to 86.45 and from 94.20 to 82.72, respectively for GP0 and GP10. Similar results have been reported in cooked wheat pasta samples formulated with increasing amount of GPP in the recipe (from 0 to 10 g/100 g \(w/w\)) [10]. This can be related to changes in the chemical composition, as well as to possible interactions among the different constituents within the food matrix, following the inclusion level of GPP in a WWF-based bread recipe [11]. In particular, some of the starch granules could be subjected to a limited starch gelatinization, due to the dietary fiber content from GPP, which may compete with starch for water absorption and/or limit the extent of gelatinization through starch encapsulation during hydrothermal processing [33]. Moreover, dietary fiber cell wall component  
\begin{table}
\begin{tabular}{c c c c c} \hline \hline
**Activity** & **Bread Sample** & \begin{tabular}{c} **Prior to Digestion** \\ **(\#M TE/100 g DM)** \\ \end{tabular} & \begin{tabular}{c} **Gastric** \\ **(\#M TE/100 g DM)** \\ \end{tabular} & \
\begin{tabular}{c} **Small Intestine** \\ **(\#M TE/100 g DM)** \\ \end{tabular} \\ \hline \multirow{3}{*}{
\begin{tabular}{c} ARAP \\ \end{tabular} } & GP0 & 199.72 \(\pm\) 9.69 \({}^{\text{a}}\) & 40.12 \(\pm\) 3.18 \({}^{\text{a}}\) & 53.71 \(\pm\) 5.37 \({}^{\text{a}}\) \\  & GP5 & 795.26 \(\pm\) 63.11 \({}^{\text{b}}\) & 169.27 \(\pm\) 17.93 \({}^{\text{b}}\) & 100.22 \(\pm\) 9.59 \({}^{\text{b}}\) \\  & GP10 & 1577.39 \(\pm\) 87.20 \({}^{\text{c}}\) & 231.44 \(\pm\) 12.43 \({}^{\text{c}}\) & 135.65 \(\pm\) 12.05 \({}^{\text{c}}\) \\  & GP0 & 240.00 \(\pm\) 7.90 \({}^{\text{a}}\) & 150.94 \(\pm\) 14.08 \({}^{\text{a}}\) & 54.47 \(\pm\) 308 \({}^{\text{a}}\) \\  & GP5 & 999.50 \(\pm\) 24.78 \({}^{\text{b}}\) & 369.17 \(\pm\) 11.40 \({}^{\text{b}}\) & 223.76 \(\pm\) 13.13 \({}^{\text{b}}\) \\  & GP10 & 1540.83 \(\pm\) 47.45 \({}^{\text{c}}\) & 426.46 \(\pm\) 10.34 \({}^{\text{c}}\) & 233.00 \(\pm\) 14.44 \({}^{\text{c}}\) \\ \hline \hline \end{tabular}
\end{table}
Table 2: In vitro antioxidant activity (as FRAP and ABTS) of control bread (GP0) and bread fortified with different percentages of grape pomace powder (GP5: 5 g/100 g GPP; and GP10: 10 g/100 g GPP) before and after the gastric and small intestine phases of in vitro simulated digestion.  
can encapsulate starch granules, thus influencing the in vitro starch digestibility through a limited access to digestive enzymes [34]. The denser matrix of GP5 and GP10 breads as compared to GP0 by means of texture analysis [11] could have also contributed to decrease the in vitro starch digestion [33; 34; 35; 36].  
Lastly, the inherent phenolic profile of the GPP, mainly phenolic acids, tannins and flavonoids, could reduce the in vitro starch digestibility, by inhibiting starch hydrolyzing enzymes and/or through non-covalent interactions with starch on cooking, leading to the formation of starch-complexes with partial enzyme accessibility [37]. Accordingly, [PERSON] et al. [38] showed that different classes of polyphenols can inhibit the activities of \(\alpha\)-amylase and \(\alpha\)-glucosidase in vitro. Also, polyphenols may limit the speed and the degree of starch gelatinization by hydrogen bonding between phenol and amylose molecules [39]. Similar results were observed in samples of bread fortified with quinoa flour [40] and mango peel powder [41], as well as in wheat-based fresh pasta formulated with increasing levels of _Moringa oleifera_ leaf powder [15].